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Cyclic tris-[5]helicenes with single and triple twisted Möbius topologies and Möbius aromaticity
G. Naulet, L. Sturm, A. Robert, P. Dechambenoit, F. Röhricht, R. Herges, H. Bock and F. Durola, Chemical Science 2019, published online.
Abstract:
A number of singly (180°) twisted, largely single-stranded and thus conformationally rather fragile, Möbius molecules have been synthesized within the last 15 years, which are aromatic with 4n electrons, thus violating the Hückel rule. Annulenes with significantly higher twist (e.g. 540°) that retain a full cyclic conjugation path have been elusive, mainly because of the high strain and loss of orbital overlap. Recently, a topological strategy was devised to project the “twist” into “writhe”, thus reducing the strain. However, orbital overlap was still severely reduced within the flexible building blocks. We now present a single and a triple twisted annulene with fully conjugated peripheries. They are unique in their pronounced band shape and conformational robustness as they are made up of three fully kata-condensed [5]helicene fragments. The triple twisted molecule exhibits a strong diatropic ring current in the outer periphery, even though the π system includes 4n electrons. The diatropic current is counterbalanced by a paratropic current in the σ system, resulting in no net manifestation of macrocyclic aromaticity. The key step of the synthesis of both Möbius compounds is a Perkin condensation of complementary bifunctional bismaleates leading to a flexible macrocycle containing alternating benzene and biphenyl fragments. Subsequent photocyclization yields a separable mixture of rigid diastereomeric tris-helicene macrocycles of the above topologies.
BibTeX:
@article{Naulet2019,
author = {Guillaume Naulet and Ludmilla Sturm and Antoine Robert and Pierre Dechambenoit and Fynn Röhricht and Rainer Herges and Harald Bock and Fabien Durola},
title = {Cyclic tris-[5]helicenes with single and triple twisted Möbius topologies and Möbius aromaticity},
journal = {Chemical Science},
publisher = {Royal Society of Chemistry (RSC)},
year = {2019},
pages = {published online},
doi = {https://doi.org/10.1039/c8sc02877j}
}
Spin in a closed-shell organic molecule on a metal substrate generated by a sigmatropic reaction
M.-L. Bocquet, N. Lorente, R. Berndt and M. Gruber, Angew. Chem. Int. Ed. 2018, 47, published online.
Abstract:
Depositing intact organic radicals on various substrates can be challenging. Generally, inert metal surfaces present more chances of hosting the intact radicals, but the large amounts of delocalized electronic states favor charge transfer and ultimately spin quenching. Reducing the molecule‐substrate interaction is a usual strategy to stabilize radicals on surfaces. To this end, thin insulating layers have been introduced to provide a controllable degree of electronic decoupling. Recently, retinoid molecules adsorbed on gold have been manipulated with a scanning tunneling microscope (STM) to exhibit a localized spin. Previous calculations have failed to find a radical derivative of the molecule on the surface. Here, we propose the formation of a neutral radical that is spatially localized in a tilted and lifted cyclic end of the molecule. The spin is created in a two‐step process: a [1,3] sigmatropic hydrogen shift yielding an allene motif and the abstraction of the shifted hydrogen atom. The allene function provokes a perpendicular tilt of the cyclic end with respect to the rest of the conjugated chain and thus localizes the spin of the dehydrogenated allene in its lifted subpart. The results of density functional theory (DFT) calculations and additional STM manipulations lend support to the proposed mechanism. This work indicates that the controlled generation of molecular spins directly on a metallic surface may be achieved with a range of closed‐shell molecules.
BibTeX:
@article{BOCQUET2018,
author = {Marie-Laure Bocquet and Nicolas Lorente and Richard Berndt and Manuel Gruber},
title = {Spin in a closed-shell organic molecule on a metal substrate generated by a sigmatropic reaction},
journal = {Angew. Chem. Int. Ed.},
publisher = {Wiley},
year = {2018},
volume = {47},
pages = {published online},
doi = {https://doi.org/10.1002/anie.201812121}
}
Ultrafast dynamics of the ESIPT photoswitch N-(3-pyridinyl)-2-pyridinecarboxamide
H. Böhnke, J. Bahrenburg, X. Ma, K. Röttger, C. Näther, M.F. Rode, A.L. Sobolewski and F. Temps, Physical Chemistry Chemical Physics 2018, 20, 2646-2655.
Abstract:
Molecular switches based on proton transfer that are photochromic and can be interconverted by light at different wavelengths back and forth between two thermodynamically stable tautomeric states in solution at room temperature are rare to date. We report on a study of the ultrafast conversion of the bistable proton transfer switch N-(3-pyridinyl)-2-pyridinecarboxamide (NPPCA) to a corresponding iminol after photoexcitation at λpump ≈ 265 nm by means of femtosecond time-resolved broad-band and single-colour transient electronic absorption spectroscopy (TEAS), transient fluorescence spectroscopy (TFLS), and transient vibrational absorption spectroscopy (TVAS) in acetonitrile solution. The interpretation of the data was accompanied by ab initio quantum chemical calculations of the excited electronic states and the vibrational frequencies of the reactant and product in their ground electronic state. The TEAS experiments provided four time constants, τ1 = 0.09 ± 0.01 ps, τ2 = 0.61 ± 0.01 ps, τ3 = 5.10 ± 0.80 ps, and τ4 = 20.0 ± 1.0 ps. The first two agree well with the measured TFLS lifetimes, τ1,TFL < 0.18 ps and τ2,TFL = 0.50 ± 0.01 ps. τ1 is related to the relaxation of the initially excited Franck–Condon (FC) state of the pyridinecarboxamide, followed by the excited-state intramolecular proton transfer (ESIPT) step to the neighbouring pyridine. The subsequent return of the molecules to the electronic ground state takes place within τ2, mediated by a conical intersection (CI) at a twisted configuration of the pyridinecarboxamide moiety. The main components in all TEAS time profiles feature a rise with τ2 and a decay with τ4 and describe subsequent molecular transformations in the electronic ground state. τ3 is ascribed to vibrational cooling of the molecules. The final iminol exhibits a permanent UV absorption at λ = 247 nm, where its absorbance is stronger than that of the carboxamide reactant. The iminol structure is unambiguously identified by the TVA spectra, which show the build-up of corresponding vibrational bands with τ4,TVA = 23 ± 2 ps after the initial bleach of the reactant vibrational bands, in excellent agreement with the TEAS data. Its lifetime is >10 ns.
BibTeX:
@article{Boehnke2018a,
author = {Hendrik Böhnke and Julia Bahrenburg and Xiaonan Ma and Katharina Röttger and Christian Näther and Michał F. Rode and Andrzej L. Sobolewski and Friedrich Temps},
title = {Ultrafast dynamics of the ESIPT photoswitch N-(3-pyridinyl)-2-pyridinecarboxamide},
journal = {Physical Chemistry Chemical Physics},
publisher = {Royal Society of Chemistry (RSC)},
year = {2018},
volume = {20},
number = {4},
pages = {2646--2655},
doi = {https://doi.org/10.1039/c7cp06145e}
}
Efficient intersystem crossing in 2-aminopurine riboside probed by femtosecond time-resolved transient vibrational absorption spectroscopy
H. Böhnke, K. Röttger, R.A. Ingle, H.J.B. Marroux, M. Bohnsack, A.J. Orr-Ewing and F. Temps, Physical Chemistry Chemical Physics 2018, 20, 20033-20042.
Abstract:
The photophysical dynamics of 2-aminopurine riboside (2APr) in CHCl3 have been studied following excitation at λpump = 310 nm by means of femtosecond transient vibrational absorption spectroscopy (TVAS) aided by quantum chemical density functional theory (DFT) and ab initio calculations. The experiments identified numerous vibrational marker bands in the regions of the NH2 stretch and the 2AP ring vibrations which could be assigned to the bleach of the S0 electronic ground state (GS) and to transient populations in the 1ππ* and 3ππ* excited electronic states. The temporal evolution of the transient vibrational bands shows that the decay of the 1ππ* population is accompanied by a partial recovery of the GS and a concurrent population of the 3ππ* state with a time constant of τ2 = 740 ± 15 ps. The ensuing electronic relaxation is concluded to proceed via the 1nπ* state as intermediate state. The absence of observable transient vibrational bands of this state hints at an upper limit for its lifetime of τ < 100 ps. The triplet quantum yield is found to be ϕT = 0.42 ± 0.07.
BibTeX:
@article{Boehnke2018,
author = {Hendrik Böhnke and Katharina Röttger and Rebecca A. Ingle and Hugo J. B. Marroux and Mats Bohnsack and Andrew J. Orr-Ewing and Friedrich Temps},
title = {Efficient intersystem crossing in 2-aminopurine riboside probed by femtosecond time-resolved transient vibrational absorption spectroscopy},
journal = {Physical Chemistry Chemical Physics},
publisher = {Royal Society of Chemistry (RSC)},
year = {2018},
volume = {20},
number = {30},
pages = {20033--20042},
doi = {https://doi.org/10.1039/c8cp02664e}
}
Coordination-Induced Spin-State Switching with Nickel(II) salpn Complexes: Electronic versus Steric Effects and Influence of Intermolecular Interactions
H. Brandenburg, J. Krahmer, K. Fischer, B. Schwager, B. Flöser, C. Näther and F. Tuczek, European Journal of Inorganic Chemistry 2018, 2018, 576-585.
Abstract:
Four nickel(II) salpn (salicylidenepropylene iminate) complexes are investigated concerning their capability to perform CISSS (coordination‐induced spin‐state switching). To this end, pyridine titration experiments are performed with the nickel salpn complexes [Ni(salpn)], [Ni(salpntBuCF3)], [Ni(salpnCF3)] and [Ni(salpnSbenz)]. The electronic‐structural changes are monitored by UV/Vis spectroscopy and Evans NMR spectroscopy. Association constants (K1s and K2), as well as thermodynamic parameters (ΔH, ΔS, and ΔG), for the binding of pyridine are determined. In comparison with porphyrins and porphyrin‐derived systems investigated earlier, the salpn systems exhibit quite different coordination properties. In particular, the fluorinated systems show the formation of dimers due to CH–π and π–π stacking. On the other hand, the investigated compounds coordinate axial ligands with affinities comparable with those of the porphyrin‐based analogs. This renders them eligible for the preparation of LD‐CISSS (light‐driven CISSS) systems, which, in turn, may be applied as functional MRI contrast agents.
BibTeX:
@article{Brandenburg2018,
author = {Hannah Brandenburg and Jan Krahmer and Kim Fischer and Bettina Schwager and Benedikt Flöser and Christian Näther and Felix Tuczek},
title = {Coordination-Induced Spin-State Switching with Nickel(II) salpn Complexes: Electronic versus Steric Effects and Influence of Intermolecular Interactions},
journal = {European Journal of Inorganic Chemistry},
publisher = {Wiley},
year = {2018},
volume = {2018},
number = {5},
pages = {576--585},
doi = {https://doi.org/10.1002/ejic.201701281}
}
Light-Mediated Growth of Noble Metal Nanostructures (Au, Ag, Cu, Pt, Pd, Ru, Ir, Rh) From Micro- and Nanoscale ZnO Tetrapodal Backbones
T.B. Demille, R.A. Hughes, A.S. Preston, R. Adelung, Y.K. Mishra and S. Neretina, Frontiers in Chemistry 2018, 6, .
Abstract:
Micro- and nanoscale ZnO tetrapods provide an attractive support for metallic nanostructures since they can be inexpensively produced using the flame transport method and nanoparticle synthesis schemes can take advantage of a coupled response facilitated by the formation of a semiconductor-metal interface. Here, we present a light-mediated solution-based growth mode capable of decorating the surface of ZnO tetrapods with nanostructures of gold, silver, copper, platinum, palladium, ruthenium, iridium, and rhodium. It involves two coupled reactions that are driven by the optical excitation of electron-hole pairs in the ZnO semiconductor by ultraviolet photons where the excited electrons are used to reduce aqueous metal ions onto the ZnO tetrapod as excited holes are scavenged from the surface. For the most part, the growth mode gives rise to nanoparticles with a roundish morphology that are uniformly distributed on the tetrapod surface. Larger structures with irregular shapes are, however, obtained for syntheses utilizing aqueous metal nitrates as opposed to chlorides, a result that suggests that the anion plays a role in shape determination. It is also demonstrated that changes to the molarity of the metal ion can influence the nanostructure nucleation rate. The catalytic activity of tetrapods decorated with each of the eight metals is assessed using the reduction of 4-nitrophenol by borohydride as a model reaction where it is shown that those decorated with Pd, Ag, and Rh are the most active.
BibTeX:
@article{Demille2018,
author = {Trevor B. Demille and Robert A. Hughes and Arin S. Preston and Rainer Adelung and Yogendra Kumar Mishra and Svetlana Neretina},
title = {Light-Mediated Growth of Noble Metal Nanostructures (Au, Ag, Cu, Pt, Pd, Ru, Ir, Rh) From Micro- and Nanoscale ZnO Tetrapodal Backbones},
journal = {Frontiers in Chemistry},
publisher = {Frontiers Media SA},
year = {2018},
volume = {6},
doi = {https://doi.org/10.3389/fchem.2018.00411}
}
Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-uplambda6-sulfanyl)acetic acid esters with aldehydes
A.-L. Dreier, A.V. Matsnev, J.S. Thrasher and G. Haufe, Beilstein Journal of Organic Chemistry 2018, 14, 373-380.
BibTeX:
@article{Dreier2018,
author = {Anna-Lena Dreier and Andrej V Matsnev and Joseph S Thrasher and Günter Haufe},
title = {Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-uplambda6-sulfanyl)acetic acid esters with aldehydes},
journal = {Beilstein Journal of Organic Chemistry},
publisher = {Beilstein Institut},
year = {2018},
volume = {14},
pages = {373--380},
doi = {https://doi.org/10.3762/bjoc.14.25}
}
Continuous Uptake or Saturation—Investigation of Concentration and Surface-Packing-Specific Hemin Interaction with Lipid Membranes
R.P. Giri, M.K. Mukhopadhyay, U.K. Basak, A. Chakrabarti, M.K. Sanyal, B. Runge and B.M. Murphy, The Journal of Physical Chemistry B 2018, 122, 7547-7554.
Abstract:
Drug design and targeted delivery in cells serve as a flourishing area not only for scientific inquiry, owing to numerous clinical applications, but also for understanding cell interaction with exogenous materials. The membrane localization of heme and its analog hemin, one of the most biologically relevant planar organic molecule, is very important to understand the molecular mechanism of intercalation and adsorption of this cytotoxic molecule after its dissociation from proteins such as hemoglobin. Herein, we investigate the differential behavior of hemin on the soft membrane surfaces of phospholipids by synchrotron-based X-ray scattering techniques, Langmuir monolayer measurements, and molecular dynamics simulation. A continuous hemin uptake from the subphase and intercalation into and/or adsorption on to the membrane surface have been witnessed in a strong membrane surface packing-specific manner. Competitive interactions between hemin-membrane and hemin–hemin are proposed to be responsible for the critical hemin concentration. Up to the limit, a continuous hemin uptake is possible and beyond that the hemin–hemin interaction dominates, effectively reducing the hemin intercalation into the membrane. This structural model of the hemin-uptake process can be generalized to understand the localization and transport across membranes and also for the development and design of new drugs.
BibTeX:
@article{Giri2018,
author = {R. P. Giri and M. K. Mukhopadhyay and U. K. Basak and A. Chakrabarti and M. K. Sanyal and B. Runge and B. M. Murphy},
title = {Continuous Uptake or Saturation—Investigation of Concentration and Surface-Packing-Specific Hemin Interaction with Lipid Membranes},
journal = {The Journal of Physical Chemistry B},
publisher = {American Chemical Society (ACS)},
year = {2018},
volume = {122},
number = {30},
pages = {7547--7554},
doi = {https://doi.org/10.1021/acs.jpcb.8b03327}
}
The Kondo resonance line shape in scanning tunnelling spectroscopy: instrumental aspects
M. Gruber, A. Weismann and R. Berndt, Journal of Physics: Condensed Matter 2018, 30, 424001.
Abstract:
In the scanning tunnelling microscope, the many-body Kondo effect leads to a zero-bias feature of the differential conductance spectra of magnetic adsorbates on surfaces. The intrinsic line shape of this Kondo resonance and its temperature dependence in principle contain valuable information. We use measurements on a molecular Kondo system, all- trans retinoic acid on Au(1 1 1), and model calculations to discuss the role of instrumental broadening. The modulation voltage used for the lock-in detection, noise on the sample voltage, and the temperature of the microscope tip are considered. These sources of broadening affect the apparent line shapes and render difficult a determination of the intrinsic line width, in particular when variable temperatures are involved.
BibTeX:
@article{Gruber2018,
author = {Manuel Gruber and Alexander Weismann and Richard Berndt},
title = {The Kondo resonance line shape in scanning tunnelling spectroscopy: instrumental aspects},
journal = {Journal of Physics: Condensed Matter},
publisher = {IOP Publishing},
year = {2018},
volume = {30},
number = {42},
pages = {424001},
doi = {https://doi.org/10.1088/1361-648x/aadfa3}
}
Noncollinear spin density of an adatom on a magnetic surface
S. Haldar and S. Heinze, Physical Review B 2018, 98, 220401(R).
Abstract:
We show that an individual adatom on a magnetic surface can exhibit a noncollinear spin density. Using density functional theory we study Co and Ir adatoms on a Mn monolayer on the W(110) surface which possesses a noncollinear canted spin structure. Due to hybridization with the nearest and next-nearest Mn atoms of the monolayer the spin direction of the underlying substrate is encoded into the orbitals of the adatom. This explains recent scanning tunneling microscopy experiments showing a spin sensitive shape asymmetry of adatoms [Serrate et al., Phys. Rev. B 93, 125424 (2016)] which confirms the intra-atomic noncollinear magnetism of the adatoms.
BibTeX:
@article{Haldar2018,
author = {Soumyajyoti Haldar and Stefan Heinze},
title = {Noncollinear spin density of an adatom on a magnetic surface},
journal = {Physical Review B},
publisher = {American Physical Society (APS)},
year = {2018},
volume = {98},
number = {22},
pages = {220401(R)},
doi = {https://doi.org/10.1103/physrevb.98.220401}
}
Corset-like solid electrolyte interface for fast charging of silicon wire anodes
S. Hansen, S. Shree, G. Neubüser, J. Carstensen, L. Kienle and R. Adelung, Journal of Power Sources 2018, 381, 8-17.
Abstract:
The most challenging tasks in today's batteries are the need for fast charging and large energy densities for longer lifetimes. Micro-structured silicon microwire anodes show a nine-fold increase in gravimetric capacity over standard graphite batteries. The anodes exhibit an areal capacity of 4.25 mAhcm−2 with a specific capacity of 3150 mAhg−1. The high specific capacity implies a 400% volume expansion of the Si wires. This paper demonstrates that by modifying and adapting the electrolyte composition a charging speed of 5 C (12 min charging time) can be reached completely maintaining the area and gravimetric capacity of the silicon anodes. Detailed analysis of the charge transfer processes across the solid electrolyte interface into the silicon wires reveals highly relevant mechanisms for this stable performance. A well-established solvent candidate, like propylene carbonate, which was rated not at all suitable for graphite electrodes, is very promising and advancing fast for pure silicon anodes. This addition into the electrolyte allows modifying the mechanical properties of the SEI layer in oder to support revery individual silicon wire to buffer the inevitable volume expansion.
BibTeX:
@article{Hansen2018,
author = {Sandra Hansen and Sindu Shree and Gero Neubüser and Jürgen Carstensen and Lorenz Kienle and Rainer Adelung},
title = {Corset-like solid electrolyte interface for fast charging of silicon wire anodes},
journal = {Journal of Power Sources},
publisher = {Elsevier BV},
year = {2018},
volume = {381},
pages = {8--17},
doi = {https://doi.org/10.1016/j.jpowsour.2018.01.085}
}
Probing long-range structural order in SnPc/Ag (111) by umklapp process assisted low-energy angle-resolved photoelectron spectroscopy
S. Jauernik, P. Hein, M. Gurgel, J. Falke and M. Bauer, Physical Review B 2018, 97, 125413.
Abstract:
Laser-based angle-resolved photoelectron spectroscopy is performed on tin-phthalocyanine (SnPc) adsorbed on silver Ag(111). Upon adsorption of SnPc, strongly dispersing bands are observed which are identified as secondary Mahan cones formed by surface umklapp processes acting on photoelectrons from the silver substrate as they transit through the ordered adsorbate layer. We show that the photoemission data carry quantitative structural information on the adsorbate layer similar to what can be obtained from a conventional low-energy electron diffraction (LEED) study. More specifically, we compare photoemission data and LEED data probing an incommensurate-to-commensurate structural phase transition of the adsorbate layer. Based on our results we propose that Mahan-cone spectroscopy operated in a pump-probe configuration can be used in the future to probe structural dynamics at surfaces with a temporal resolution in the sub-100-fs regime.
BibTeX:
@article{Jauernik2018,
author = {Jauernik, Stephan and Hein, Petra and Gurgel, Max and Falke, Julian and Bauer, Michael},
title = {Probing long-range structural order in SnPc/Ag (111) by umklapp process assisted low-energy angle-resolved photoelectron spectroscopy},
journal = {Physical Review B},
publisher = {APS},
year = {2018},
volume = {97},
number = {12},
pages = {125413},
doi = {https://doi.org/10.1103/PhysRevB.97.125413}
}
Spin control induced by molecular charging in a transport junction
S. Karan, C. Garcia, M. Karolak, D. Jacob, N. Lorente and R. Berndt, Nano letters 2018, 18, 88-93.
Abstract:
The ability of molecules to maintain magnetic multistability in nanoscale-junctions will determine their role in downsizing spintronic devices. While spin-injection from ferromagnetic leads gives rise to magnetoresistance in metallic nanocontacts, nonmagnetic leads probing the magnetic states of the junction itself have been considered as an alternative. Extending this experimental approach to molecular junctions, which are sensitive to chemical parameters, we demonstrate that the electron affinity of a molecule decisively influences its spin transport. We use a scanning tunneling microscope to trap a meso-substituted iron porphyrin, putting the iron center in an environment that provides control of its charge and spin states. A large electron affinity of peripheral ligands is shown to enable switching of the molecular S = 1 ground state found at low electron density to S = 1/2 at high density, while lower affinity keeps the molecule inactive to spin-state transition. These results pave the way for spin control using chemical design and electrical means.
BibTeX:
@article{Karan2017,
author = {Karan, Sujoy and Garcia, Carlos and Karolak, Michael and Jacob, David and Lorente, Nicolás and Berndt, Richard},
title = {Spin control induced by molecular charging in a transport junction},
journal = {Nano letters},
publisher = {ACS Publications},
year = {2018},
volume = {18},
pages = {88-93},
doi = {https://doi.org/10.1021/acs.nanolett.7b03411}
}
Evolution of cooperativity in the spin transition of an iron(II) complex on a graphite surface
L. Kipgen, M. Bernien, S. Ossinger, F. Nickel, A.J. Britton, L.M. Arruda, H. Naggert, C. Luo, C. Lotze, H. Ryll, F. Radu, E. Schierle, E. Weschke, F. Tuczek and W. Kuch, Nature Communications 2018, 9, .
Abstract:
Cooperative effects determine the spin-state bistability of spin-crossover molecules (SCMs). Herein, the ultimate scale limit at which cooperative spin switching becomes effective is investigated in a complex [Fe(H2B(pz)2)2(bipy)] deposited on a highly oriented pyrolytic graphite surface, using x-ray absorption spectroscopy. This system exhibits a complete thermal- and light-induced spin transition at thicknesses ranging from submonolayers to multilayers. On increasing the coverage from 0.35(4) to 10(1) monolayers, the width of the temperature-induced spin transition curve narrows significantly, evidencing the buildup of cooperative effects. While the molecules at the submonolayers exhibit an apparent anticooperative behavior, the multilayers starting from a double-layer exhibit a distinctly cooperative spin switching, with a free-molecule-like behavior indicated at around a monolayer. These observations will serve as useful guidelines in designing SCM-based devices.
BibTeX:
@article{Kipgen2018,
author = {Lalminthang Kipgen and Matthias Bernien and Sascha Ossinger and Fabian Nickel and Andrew J. Britton and Lucas M. Arruda and Holger Naggert and Chen Luo and Christian Lotze and Hanjo Ryll and Florin Radu and Enrico Schierle and Eugen Weschke and Felix Tuczek and Wolfgang Kuch},
title = {Evolution of cooperativity in the spin transition of an iron(II) complex on a graphite surface},
journal = {Nature Communications},
publisher = {Springer Nature America, Inc},
year = {2018},
volume = {9},
number = {1},
doi = {https://doi.org/10.1038/s41467-018-05399-8}
}
Design, synthesis, and evaluation of nickel dipyridylmethane complexes for Coordination-Induced Spin State Switching (CISSS)
M. Klaß, J. Krahmer, C. Näther and F. Tuczek, Dalton Transactions 2018, 47, 1261-1275.
Abstract:
In order to develop a new system capable of performing Ligand-Driven Coordination-Induced Spin State Switching (LD-CISSS), a new CISSS complex based on a nickel(II) dipyridylmethane framework was rationally designed, synthesized, and investigated both experimentally and theoretically. In DFT calculations, a dipyridylmethane dicarboxylic acid ligand was determined to be most suitable for this purpose. The corresponding nickel(II) complex was synthesized by an optimized procedure, and the CISSS effect was evidenced by crystallography as well as Evans NMR susceptibility measurements. In the solid state, the square planar nickel complex is diamagnetic and the octahedral bispyridine adduct is paramagnetic. Also, a dimer containing three ethanol ligands was obtained. Dimer formation occurs in solution as well. Upon addition of pyridine, a continuous transition from predominantly diamagnetic to paramagnetic behavior takes place. Equilibrium constants for the binding of pyridine as well as corresponding thermodynamic parameters indicate a high affinity for this ligand and show that the title system is a suitable candidate for LD-CISSS.
BibTeX:
@article{Klas2018,
author = {Michaela Klaß and Jan Krahmer and Christian Näther and Felix Tuczek},
title = {Design, synthesis, and evaluation of nickel dipyridylmethane complexes for Coordination-Induced Spin State Switching (CISSS)},
journal = {Dalton Transactions},
publisher = {Royal Society of Chemistry (RSC)},
year = {2018},
volume = {47},
number = {4},
pages = {1261--1275},
doi = {https://doi.org/10.1039/c7dt03952b}
}
Crystal structure of (methanol-upkappaO)[5,10,15,20-tetrakis(2-aminophenyl)porphyrinato-upkappa4 N]zinc(II)–chloroform–methanol (1/1/1)
L. Leben, C. Näther and R. Herges, Acta Crystallographica Section E Crystallographic Communications 2018, 74, 1285-1289.
Abstract:
In the crystal structure of the title compound, [Zn(C44H32N8)(CH3OH)]·CHCl3·CH3OH, the ZnII cation is coordinated by four porphyrin N and one methanol O atom within a slightly distorted square-pyramidal environment and is shifted out of the porphyrin plane towards the direction of the methanol mol­ecule. The methyl group of the coordinating methanol mol­ecule is disordered over two sets of sites. The porphyrin backbone is nearly planar and the phenyl rings are almost perpendicular to the porphyrin plane. As is typical for picket-fence porphyrins, all four ortho substituents of the meso-phenyl groups (here the amino groups) are facing to the same side of the porphyrin mol­ecule. In the crystal structure, two neighbouring porphyrin complexes form centrosymmetric dimers that are connected via O—H...N hydrogen bonding. With the aid of additional N—H...N and C—H...N hydrogen bonding, these dimers are stacked into columns parallel to [010] that are finally arranged into layers parallel to (001). Between these layers channels are formed where chloro­form solvent mol­ecules are located that are connected to the porphyrin complexes by weak C—H...Cl hydrogen bonding. There are additional cavities in the structure where some small residual electron density is found, indicating the presence of disordered methanol mol­ecules, but a reasonable model could not be refined. Therefore the contribution of the electron density associated with the methanol solvent mol­ecule was removed with the SQUEEZE procedure [Spek (2015). Acta Cryst. C71, 9–18] in PLATON. Nevertheless, the given chemical formula and other crystal data take into account the methanol solvent mol­ecule.
BibTeX:
@article{Leben2018a,
author = {Lisa Leben and Christian Näther and Rainer Herges},
title = {Crystal structure of (methanol-upkappaO)[5,10,15,20-tetrakis(2-aminophenyl)porphyrinato-upkappa4 N]zinc(II)–chloroform–methanol (1/1/1)},
journal = {Acta Crystallographica Section E Crystallographic Communications},
publisher = {International Union of Crystallography (IUCr)},
year = {2018},
volume = {74},
number = {9},
pages = {1285--1289},
doi = {https://doi.org/10.1107/s205698901801099x}
}
Crystal structure of (diethyl ether-upkappaO)[5,10,15,20-tetrakis(2-isothiocyanatophenyl)porphyrinato-upkappa4 N]zinc diethyl ether solvate
L. Leben, E. Schaub, C. Näther and R. Herges, Acta Crystallographica Section E Crystallographic Communications 2018, 74, 1609-1612.
Abstract:
The crystal structure of the title compound, [Zn(C48H24N8S4)(C4H10O)]·C4H10O, consists of discrete porphyrin complexes that are located on a twofold rotation axis. The ZnII cation is fivefold coordinated by four N atoms of the porphyrin moiety and one O atom of a diethyl ether mol­ecule in a slightly distorted square-pyramidal environment with the diethyl ether mol­ecule in the apical position. The porphyrin backbone is nearly planar with the metal cation slightly shifted out of the plane towards the coordinating diethyl ether mol­ecule. All four iso­thio­cyanato groups of the phenyl substituents at the meso-positions face the same side of the porphyrin, as is characteristic for picket fence porphyrins. In the crystal structure, the discrete porphyrin complexes are arranged in such a way that cavities are formed in which additional diethyl ether solvate mol­ecules are located around a twofold rotation axis. The O atom of the solvent mol­ecule is not positioned exactly on the twofold rotation axis, thus making the whole mol­ecule equally disordered over two symmetry-related positions.
BibTeX:
@article{Leben2018,
author = {Lisa Leben and Eike Schaub and Christian Näther and Rainer Herges},
title = {Crystal structure of (diethyl ether-upkappaO)[5,10,15,20-tetrakis(2-isothiocyanatophenyl)porphyrinato-upkappa4 N]zinc diethyl ether solvate},
journal = {Acta Crystallographica Section E Crystallographic Communications},
publisher = {International Union of Crystallography (IUCr)},
year = {2018},
volume = {74},
number = {11},
pages = {1609--1612},
doi = {https://doi.org/10.1107/s2056989018014238}
}
ZnO tetrapod materials for functional applications
Y.K. Mishra and R. Adelung, Materials Today 2018, 21, 631-651.
Abstract:
In the last 15 years, more than 50,000 papers with zinc oxide (ZnO) in the title are listed within ISI database. The outstanding popularity of ZnO has many reasons; the most important one appears to be its multi-functionality, resulting in applications in physics, chemistry, electrical engineering, material science, energy, textile, rubber, additive manufacturing, cosmetics, and pharmaceutical or medicine, as well as the ease to grow all kinds of nano- and microstructures. A key structure is the tetrapod-shaped ZnO (T-ZnO), which we want to focus on in this mini-review to demonstrate the remarkable properties and multifunctionality of ZnO and motivate why even much more research and applications are likely to come in near future. As T-ZnO came into focus again mainly during the last 10 years, the big data problem in T-ZnO is not as severe as in ZnO; nevertheless, a complete overview is impossible. However, this brief T-ZnO overview attempts to cover the scopes toward advanced technologies; nanoelectronics/optoelectronics sensing devices; multifunctional composites/coatings; novel biomedical engineering materials; versatile energy harvesting candidates; and unique structures for applications in chemistry, cosmetics, pharmaceuticals, food, agriculture, engineering technologies, and many others. The 3D nanotechnology is a current mainstream in materials science/nanotechnology research, and T-ZnO contributes to this field by its simple synthesis of porous networks as sacrificial templates for any desired new cellular materials.
BibTeX:
@article{Mishra2018,
author = {Yogendra Kumar Mishra and Rainer Adelung},
title = {ZnO tetrapod materials for functional applications},
journal = {Materials Today},
publisher = {Elsevier BV},
year = {2018},
volume = {21},
number = {6},
pages = {631--651},
doi = {https://doi.org/10.1016/j.mattod.2017.11.003}
}
Zinc oxide nanotetrapods with four different arm morphologies for versatile nanosensors
I. Paulowicz, V. Postica, O. Lupan, N. Wolff, S. Shree, A. Cojocaru, M. Deng, Y.K. Mishra, I. Tiginyanu, L. Kienle and R. Adelung, Sensors and Actuators B: Chemical 2018, 262, 425-435.
Abstract:
The structural morphology of metal oxide nano- and microstructures plays a crucial role in the performances of sensors and especially of nanosensors. Here, a simple approach on the synthesis of three-dimensional (3D) highly porous ZnO nano- and microstructure networks with four different arm morphologies in the same process is reported. Systematic studies about the growth of micro- and nanotetrapods were performed and the corresponding mechanism has been discussed in detail. The difference in the morphologies of the obtained structures was understood on the basis of synthesis temperature variations, content of Zn vapor and oxygen in the furnace at different locations, which result in different growth rates along the ZnO c-axis. The approach developed in this work gives the possibility to simultaneously grow the interconnected networks of nano-ZnO-tetrapods (T), ZnO-T, with complex arm morphologies, ZnO-T-nanosheets, and ZnO nanowires (NW)-T. The obtained free-standing network material was integrated in an electronic device for gas/vapor sensing investigations. The individual structures with different morphologies (NW with a diameter down to 30 nm, two interconnected NWs, microsheets, and nanotetrapods with a diameter of the arms in the range of 40–80 nm) were integrated into nanosensor devices in order to investigate the influence of the morphology on the electrical and gas sensing properties. The results showed higher (S ≈ 510–2500 ppm) ammonia vapor sensing properties of ZnO-T compared to ZnO-T-nanosheets and ZnO-NW-T, revealing the importance of nano-junctions in nano-sensor devices. The presented approach offers the possibility to understand the importance of exposed facets and junctions on the sensing properties of such nanostructures. These results offer new opportunities for further experimental and fundamental studies of oxide morphologies in the context of nanosensor applications for environmental monitoring.
BibTeX:
@article{Paulowicz2018,
author = {Ingo Paulowicz and Vasile Postica and Oleg Lupan and Niklas Wolff and Sindu Shree and Ala Cojocaru and Mao Deng and Yogendra Kumar Mishra and Ion Tiginyanu and Lorenz Kienle and Rainer Adelung},
title = {Zinc oxide nanotetrapods with four different arm morphologies for versatile nanosensors},
journal = {Sensors and Actuators B: Chemical},
publisher = {Elsevier BV},
year = {2018},
volume = {262},
pages = {425--435},
doi = {https://doi.org/10.1016/j.snb.2018.01.206}
}
Axitinib - A Photoswitchable Approved Tyrosine Kinase Inhibitor
C. Peifer, D. Schmidt, T. Rodat, L. Heintze, J. Weber, R. Horbert, U. Girreser, T. Raeker, L. Bußmann, M. Kriegs and B. Hartke, ChemMedChem 2018, .
Abstract:
The goal of photopharmacology is to develop photoswitchable enzyme modulators as tunable (pro-)drugs that can be spatially and temporally controlled by light. In this context we became interested in the tyrosine kinase inhibitor axitinib that exhibits a photosensitive stilbene-like moiety allowing for E/Z-isomerization. Axitinib is an approved drug targeting the vascular
endothelial growth factor receptor 2 (VEGFR2) and is licensed for second-line therapy of renal cell carcinoma. We investigated the photoinduced E/Z isomerization of axitinib to explore if its inhibitory effect can be turned “on” and “off”, triggered by light. Under controlled light conditions we could demonstrate that (Z)-axitinib is 43 times less active compared to the (E)-isomer in an VEGFR2 assay. Furthermore, we proved that kinase activity in human umbilical vein cells (HUVECs) is reduced by (E)-axitinib, but only weakly affected by (Z)-axitinib. By irradiating (Z)-axitinib in vitro with UV light (385 nm) it is possible to switch it almost quantitatively to the (E)-isomer and to completely restore the biological activity of (E)-axitinib. However, vice versa switching the biological activity “off” from (E)- to (Z)-axitinib was not possible in aqueous solution due to a competing irreversible [2+2]-photocycloaddition yielding a biologically inactive axitinib-dimer.
BibTeX:
@article{Peifer2018,
author = {Christian Peifer and Dorian Schmidt and Theo Rodat and Linda Heintze and Jantje Weber and Rebecca Horbert and Ulrich Girreser and Tim Raeker and Lara Bußmann and Malte Kriegs and Bernd Hartke},
title = {Axitinib - A Photoswitchable Approved Tyrosine Kinase Inhibitor},
journal = {ChemMedChem},
publisher = {Wiley},
year = {2018},
doi = {https://doi.org/10.1002/cmdc.201800531}
}
Insertion of Ni(I) into Porphyrins at Room Temperature: Preparation of Ni(II)porphyrins, and Ni(II)chlorins and Observation of Hydroporphyrin Intermediates.
M.K. Peters and R. Herges, Inorganic Chemistry 2018, 57, 3177-3182.
Abstract:
Reduced Nickel porphyrins play an important role as enzymatic cofactors in the global carbon cycle (cofactor F430), and as powerful catalysts in solar-to-fuel-processes such as the hydrogen evolution reaction, and the reduction of CO and CO . The preparation of Ni(II)porphyrins requires harsh conditions, and characterization of the reduced species is intricate. We present a very mild, convenient, and high yielding method of inserting Ni into electron rich, and electron deficient porphyrins which at the same time gives access to to Ni(II) phlorins and Ni(II)chlorins and Ni(II)porphyrins.
BibTeX:
@article{Peters2018a,
author = {Peters, Morten K and Herges, Rainer},
title = {Insertion of Ni(I) into Porphyrins at Room Temperature: Preparation of Ni(II)porphyrins, and Ni(II)chlorins and Observation of Hydroporphyrin Intermediates.},
journal = {Inorganic Chemistry},
year = {2018},
volume = {57},
pages = {3177--3182},
doi = {https://doi.org/10.1021/acs.inorgchem.7b03164}
}
Crystal structure of 2-[2-(pyridin-3-yl) diazen-1-yl] aniline
M.K. Peters, C. Näther and R. Herges, Acta Crystallographica Section E: Crystallographic Communications 2018, 74, 1013-1016.
Abstract:
The crystal structure of the title compd., C11H10N4, comprises mols. in a trans conformation for which all the atoms are located in general positions. The six-​membered rings are coplanar and this arrangement might be stabilized by intramol. N-​H···N hydrogen bonding. In the crystal, the mols. are linked into helical chains parallel to the b axis via N-​H···N hydrogen bonding. The mol. packing shows a herringbone-​like pattern along the a axis. Comparison of the X-​ray powder diffraction with that calcd. from single crystal data proves that a pure cryst. phase was obtained and UV-​Vis measurements reveal that only the trans isomer is present.
BibTeX:
@article{Peters2018,
author = {Peters, Morten K and Näther, Christian and Herges, Rainer},
title = {Crystal structure of 2-[2-(pyridin-3-yl) diazen-1-yl] aniline},
journal = {Acta Crystallographica Section E: Crystallographic Communications},
publisher = {International Union of Crystallography},
year = {2018},
volume = {74},
number = {7},
pages = {1013--1016},
doi = {https://doi.org/10.1107/S2056989018008605}
}
Microwave-Assisted Facile Synthesis of Red-Shifted Azobenzene Glycoconjugates
V. Poonthiyil, F. Reise, G. Despras and T.K. Lindhorst, European Journal of Organic Chemistry 2018, 6241-6248.
Abstract:
Azobenzene glycoconjugates are important tools used to study the effect of sugar orientation in molecular recognition. This is possible through the reversible photoinduced trans/cis isomerization of the N=N double bond in the sugar‐presenting azobenzene units. However, all the azobenzene glycoconjugates used so far need ultraviolet light for trans‐to‐cis switching, restricting their use in in vivo applications. Herein, we report the first synthesis of red‐shifted azobenzene glycoconjugates. After tetra‐ortho‐chlorination of the azobenzene moiety, the respective glycoazobenzenes can be switched from the trans to the cis state with visible light. We report scope and limitations of microwave‐assisted late‐stage C–H chlorination to afford tetra‐ortho‐chloroazobenzene glycoconjugates. Furthermore, synthesis of a red‐shifted azobenzene glycoconjugate carrying a thioacetate‐terminated linker is reported to allow for fabrication of red‐shifted photoswitchable glyco‐SAMs on gold surface. The photochromic properties of all red‐shifted azobenzene glycoconjugates are described.
BibTeX:
@article{Poonthiyil2018,
author = {Vivek Poonthiyil and Franziska Reise and Guillaume Despras and Thisbe K. Lindhorst},
title = {Microwave-Assisted Facile Synthesis of Red-Shifted Azobenzene Glycoconjugates},
journal = {European Journal of Organic Chemistry},
publisher = {Wiley},
year = {2018},
number = {45},
pages = {6241--6248},
doi = {https://doi.org/10.1002/ejoc.201801078}
}
Simulations of optically switchable molecular machines for particle transport
T. Raeker, B. Jansen, D. Behrens and B. Hartke, Journal of Computational Chemistry 2018, 39, 1433-1443.
Abstract:
A promising application for design and deployment of molecular machines is nanoscale transport, driven by artificial cilia. In this contribution, we present several further steps toward this goal, beyond our first-generation artificial cilium (Raeker et al., J. Phys. Chem. A 2012, 116, 11241). Promising new azobenzene-derivatives were tested for use as cilium motors. Using a QM/MM
partitioning in on-the-fly photodynamics, excited-state surface-hopping trajectories were calculated for each isomerization direction and each motor version. The methods used were re-parametrized semiempirical quantum chemistry together with floating-occupation configuration interaction as the QM part and the OPLSAA-L forcefield as MM part. In addition, we simulated
actual particle transport by a single cilium attached to a model surface, with varying attachment strengths and modes, and with transport targets ranging from single atoms to multi-molecule arrangements. Our results provide valuable design guidelines for cilia-driven nanoscale transport and emphasize the need to carefully select the whole setup (not just the cilium itself, but also its surface attachment and the dynamic cilium-target interaction) to achieve true transport.
BibTeX:
@article{Raeker2018,
author = {Tim Raeker and Björn Jansen and Dominik Behrens and Bernd Hartke},
title = {Simulations of optically switchable molecular machines for particle transport},
journal = {Journal of Computational Chemistry},
publisher = {Wiley},
year = {2018},
volume = {39},
number = {20},
pages = {1433--1443},
doi = {https://doi.org/10.1002/jcc.25212}
}
Photoswitchable Glycolipid Mimetics: Synthesis and Photochromic Properties of Glycoazobenzene Amphiphiles
F. Reise, J.E. Warias, K. Chatterjee, N.R. Krekiehn, O. Magnussen, B.M. Murphy and T.K. Lindhorst, Chemistry - A European Journal 2018, published online.
Abstract:
Glycolipids as constituents of cell membranes play an important role in cell membrane functioning. To enable the structural modification of membranes on demand, embedding of photosensitive glycolipid mimetics was envisioned and novel amphiphilic glycolipid mimetics comprising a photoswitchable azobenzene unit were synthesized. In this study, the photochromic properties of these glycolipid mimetics were analyzed by means of UV/Vis spectroscopy and reversible photoswitching. The glycolipids were based on a racemic glycerolipid derivative to be comparable in DPPC (dipalmitoylphosphatidylcholine) phospholipid membrane monolayers. Carbohydrate head groups were altered between a β‐glucoside and a β‐lactosyl unit, as well as acyl chain lengths between C12 and C16, resulting in altered photoswitching. Langmuir isotherms showed that photoswitching of Langmuir films comprising the synthetic photosensitive glycoamphiphiles was successful.
BibTeX:
@article{Reise2018,
author = {Franziska Reise and Jonas E. Warias and Kuntal Chatterjee and Nicolai R. Krekiehn and Olaf Magnussen and Bridget M. Murphy and Thisbe K. Lindhorst},
title = {Photoswitchable Glycolipid Mimetics: Synthesis and Photochromic Properties of Glycoazobenzene Amphiphiles},
journal = {Chemistry - A European Journal},
publisher = {Wiley},
year = {2018},
pages = {published online},
doi = {https://doi.org/10.1002/chem.201803112}
}
Light-Induced Spin Crossover in an Fe(II) Low-Spin Complex Enabled by Surface Adsorption
S. Rohlf, M. Gruber, B.M. Flöser, J. Grunwald, S. Jarausch, F. Diekmann, M. Kalläne, T. Jasper-Toennies, A. Buchholz, W. Plass, R. Berndt, F. Tuczek and K. Rossnagel, The Journal of Physical Chemistry Letters 2018, 9, 1491-1496.
Abstract:
Understanding and controlling the spin-crossover properties of molecular complexes can be of particular interest for potential applications in molecular spintronics. Using near-edge X-ray absorption fine structure spectroscopy, we investigated these properties for a new vacuum-evaporable Fe(II) complex, namely [Fe(pypyr(CF3)2)2(phen)] (pypyr = 2-(2′-pyridyl)pyrrolide, phen = 1,10-phenanthroline). We find that the spin-transition temperature, well above room temperature for the bulk compound, is drastically lowered for molecules arranged in thin films. Furthermore, while within the experimentally accessible temperature range (2 K < T < 410 K) the bulk material shows indication of neither light-induced excited spin-state trapping nor soft X-ray-induced excited spin-state trapping, these effects are observed for molecules within thin films up to temperatures around 100 K. Thus, by arranging the molecules into thin films, a nominal low-spin complex is effectively transformed into a spin-crossover complex.
BibTeX:
@article{Rohlf0,
author = {Rohlf, Sebastian and Gruber, Manuel and Flöser, Benedikt M. and Grunwald, Jan and Jarausch, Simon and Diekmann, Florian and Kalläne, Matthias and Jasper-Toennies, Torben and Buchholz, Axel and Plass, Winfried and Berndt, Richard and Tuczek, Felix and Rossnagel, Kai},
title = {Light-Induced Spin Crossover in an Fe(II) Low-Spin Complex Enabled by Surface Adsorption},
journal = {The Journal of Physical Chemistry Letters},
year = {2018},
volume = {9},
pages = {1491-1496},
doi = {https://doi.org/10.1021/acs.jpclett.8b00338}
}
Synthesis of mono-functionalized S-diazocines via intramolecular Baeyer–Mills reactions
M. Schehr, D. Hugenbusch, T. Moje, C. Näther and R. Herges, Beilstein Journal of Organic Chemistry 2018, 14, 2799-2804.
Abstract:
Herein we report a reliable method to synthesize mono-functionalized S-diazocines in reproducible yields via intramolecular Baeyer–Mills reactions. Diazocines exhibit excellent photoswitchable properties. As opposed to azobenzenes they are more stable in their cis configuration. Particularly in photopharmacology mono-functionalized diazocines should be potentially useful and
superior to the frequently used azobenzenes because the sterically more demanding cis configuration should be inactive, and the slender trans configuration should fit in a tight binding pocket of a receptor. Hence, it should be possible to administer the stabile inactive compound and switch it on at the site of illness with visible light. To date only a limited number of diazocine derivatives have been published of which most are symmetrically functionalized. Using the Baeyer–Mills reaction for the synthesis of diazocines opens a novel and convenient access to unsymmetrically substituted diazocines.
BibTeX:
@article{Schehr2018,
author = {Miriam Schehr and Daniel Hugenbusch and Tobias Moje and Christian Näther and Rainer Herges},
title = {Synthesis of mono-functionalized S-diazocines via intramolecular Baeyer–Mills reactions},
journal = {Beilstein Journal of Organic Chemistry},
publisher = {Beilstein Institut},
year = {2018},
volume = {14},
pages = {2799--2804},
doi = {https://doi.org/10.3762/bjoc.14.257}
}
Tunneling anisotropic magnetoresistance via molecular \pi orbitals of Pb dimers
J. Schöneberg, P. Ferriani, S. Heinze, A. Weismann and R. Berndt, Phys. Rev. B 2018, 97, 041114.
Abstract:
Pb dimers on a ferromagnetic surface are shown to exhibit large tunneling anisotropic magnetoresistance (TAMR) due to molecular π orbitals. Dimers oriented differently with respect to the magnetization directions of a ferromagnetic Fe double layer on W(110) were made with a scanning tunneling microscope. Depending on the dimer orientations, TAMR is absent or as large as 20% at the Fermi level. General arguments and first-principles calculations show that mixing of molecular orbitals due to spin-orbit coupling, which leads to TAMR, is maximal when the magnetization is oriented parallel to the dimer axis.
BibTeX:
@article{Schoeneberg2018,
author = {Schöneberg, Johannes and Ferriani, Paolo and Heinze, Stefan and Weismann, Alexander and Berndt, Richard},
title = {Tunneling anisotropic magnetoresistance via molecular \pi orbitals of Pb dimers},
journal = {Phys. Rev. B},
publisher = {American Physical Society},
year = {2018},
volume = {97},
pages = {041114},
doi = {https://doi.org/10.1103/PhysRevB.97.041114}
}
Light-controlled switching of the spin state of iron(III)
S. Shankar, M. Peters, K. Steinborn, B. Krahwinkel, F.D. Sönnichsen, D. Grote, W. Sander, T. Lohmiller, O. Rüdiger and R. Herges, Nature Communications 2018, 9, 4750.
Abstract:
Controlled switching of the spin state of transition metal ions, particularly of FeII and FeIII, is a prerequisite to achieve selectivity, efficiency, and catalysis in a number of metalloenzymes. Here we report on an iron(III) porphyrin with a photochromic axial ligand which, upon irradiation with two different wavelengths reversibly switches its spin state between low-spin (S = 1/2) and high-spin (S = 5/2) in solution (DMSO-acetone, 2:598). The switching efficiency is 76% at room temperature. The system is neither oxygen nor water sensitive, and no fatigue was observed after more than 1000 switching cycles. Concomitant with the spin-flip is a change in redox potential by  60 mV. Besides serving as a simple model for the first step of the cytochrome P450 catalytic cycle, the spin switch can be used to switch the spin-lattice relaxation time T1 of the water protons by a factor of 15.
BibTeX:
@article{Shankar2018,
author = {Sreejith Shankar and Morten Peters and Kim Steinborn and Bahne Krahwinkel and Frank D. Sönnichsen and Dirk Grote and Wolfram Sander and Thomas Lohmiller and Olaf Rüdiger and Rainer Herges},
title = {Light-controlled switching of the spin state of iron(III)},
journal = {Nature Communications},
publisher = {Springer Nature America, Inc},
year = {2018},
volume = {9},
number = {1},
pages = {4750},
doi = {https://doi.org/10.1038/s41467-018-07023-1}
}
Buckminsterfullerene hybridized zinc oxide tetrapods: defects and charge transfer induced optical and electrical response
D. Smazna, J. Rodrigues, S. Shree, V. Postica, G. Neubüser, A.F. Martins, N.B. Sedrine, N.K. Jena, L. Siebert, F. Schütt, O. Lupan, R. Ahuja, M.R. Correia, T. Monteiro, L. Kienle, Y. Yang, R. Adelung and Y.K. Mishra, Nanoscale 2018, 10, 10050-10062.
Abstract:
Buckminster fullerene (C60) based hybrid metal oxide materials are receiving considerable attention because of their excellent fundamental and applied aspects, like semiconducting, electron transfer, luminescent behaviors, etc. and this work briefly discusses the successful fabrication of C60 decorated ZnO tetrapod materials and their detailed structure–property relationships including device sensing applications. The electron microscopy investigations indicate that a quite dense surface coverage of ZnO tetrapods with C60 clusters is achieved. The spectroscopy studies confirmed the identification of the C60 vibrational modes and the C60 induced changes in the absorption and luminescence properties of the ZnO tetrapods. An increased C60 concentration on ZnO results in steeper ZnO bandgap absorption followed by well-defined free exciton and 3.31 eV line emissions. As expected, higher amounts of C60 increase the intensity of C60-related visible absorption bands. Pumping the samples with photons with an energy corresponding to these absorption band maxima leads to additional emission from ZnO showing an effective charge transfer phenomenon from C60 to the ZnO host. The density of states model obtained from DFT studies for pure and C60 coated ZnO surfaces confirms the experimental observations. The fabricated C60–ZnO hybrid tetrapod based micro- and nanodevices showed interesting ethanol gas sensing characteristics.
BibTeX:
@article{Smazna2018,
author = {Daria Smazna and Joana Rodrigues and Sindu Shree and Vasile Postica and Gero Neubüser and A. F. Martins and N. Ben Sedrine and Naresh K. Jena and Leonard Siebert and Fabian Schütt and Oleg Lupan and Rajeev Ahuja and M. R. Correia and Teresa Monteiro and Lorenz Kienle and Ya Yang and Rainer Adelung and Yogendra Kumar Mishra},
title = {Buckminsterfullerene hybridized zinc oxide tetrapods: defects and charge transfer induced optical and electrical response},
journal = {Nanoscale},
publisher = {Royal Society of Chemistry (RSC)},
year = {2018},
volume = {10},
number = {21},
pages = {10050--10062},
doi = {https://doi.org/10.1039/c8nr01504j}
}
Structure of a Phthalocycnine Dye on ZnO
H. Zheng, Y. Xu, G.-C. Dong, J. Kröger and R. Berndt, Surface Review and Letters 2018, 1850204.
Abstract:
Room temperature scanning tunneling microscopy was used to investigate the adsorption of a dye molecule, iron-phthalocyanine (FePc), on ZnO(0001). Submolecular resolution reveals the orientation of molecules with respect to crystallographic directions of the surface. Upon adsorption, the molecular symmetry is reduced. First-principles calculations trace these observations to a strong molecule-substrate bond, which induces deformations of the molecule.
BibTeX:
@article{ZHENG2018,
author = {Hao Zheng and Yong Xu and Guo-Cai Dong and Jörg Kröger and Richard Berndt},
title = {Structure of a Phthalocycnine Dye on ZnO},
journal = {Surface Review and Letters},
publisher = {World Scientific Pub Co Pte Lt},
year = {2018},
pages = {1850204},
doi = {https://doi.org/10.1142/s0218625x18502049}
}
Submolecular resolution in scanning probe images of Sn-phthalocyanines on Cu (100) using metal tips.
K. Buchmann, N. Hauptmann, A.S. Foster and R. Berndt, Journal of physics. Condensed matter 2017, 394004.
Abstract:
Single Sn-phthalocyanine (SnPc) molecules adsorb on Cu(1 0 0) with the Sn ion above (Sn-up) or below (Sn-down) the molecular plane. Here we use a combination of atomic force microscopy (AFM), scanning tunnelling microscopy (STM) and first principles calculations to understand the adsorption configuration and origin of observed contrast of molecules in the Sn-down state. AFM with metallic tips images the pyrrole nitrogen atoms in these molecules as attractive features while STM reveals a chirality of the electronic structure of the molecules close to the Fermi level E_rm F, which is not observed in AFM. Using density functional theory calculations, the origin of the submolecular contrast is analysed and, while the electrostatic forces turn out to be negligible, the van der Waals interaction between the phenyl rings of SnPc and the substrate deform the molecule, push the pyrrole nitrogen atoms away from the substrate and thus induce the observed submolecular contrast. Simulated STM images reproduce the chirality of the electronic structure near E_rm F.
BibTeX:
@article{Buchmann2017,
author = {Buchmann, Kristof and Hauptmann, Nadine and Foster, Adam S and Berndt, Richard},
title = {Submolecular resolution in scanning probe images of Sn-phthalocyanines on Cu (100) using metal tips.},
journal = {Journal of physics. Condensed matter},
year = {2017},
pages = {394004},
doi = {https://doi.org/10.1088/1361-648X/aa7dbd}
}
Designing a molecular magnetic button based on 4 d and 5 d transition-metal phthalocyanines
P. Ferriani, S. Heinze and V. Bellini, Scientific Reports 2017, 7, 3647.
Abstract:
The field of molecular spintronics exploits the properties of organic molecules possessing a magnetic moment, either native in the form of radicals or induced by the insertion of transition metal magnetic ions. To realize logic or storage molecular spin-tronics devices, molecules with stable different magnetic states should be deposited on a substrate, and switching between the states controllably achieved. By means of a first-principles calculations, we have devised a functional molecule exhibiting different magnetic states upon structural changes induced by current injection. We investigate the prototypical case of non-planar M-Phthalocyanine (MPc), where M is a transition-metal ion belonging to the 4d and 5d series. We find that for ZrPc and HfPc deposited on a graphene decorated Ni(111) substrate, two different structural conformations could be stabilized, for which the molecules attain different magnetic states depending on the position of the M ion – whether above the Pc or between the Pc and the substrate –, acting therefore as molecular magnetic button. Our work indicates an intuitive way to engineer a magnetic molecular switch with tailored properties, starting from the knowledge of the basic atomic properties of elements and surfaces.
BibTeX:
@article{Ferriani2017,
author = {Ferriani, P and Heinze, S and Bellini, V},
title = {Designing a molecular magnetic button based on 4 d and 5 d transition-metal phthalocyanines},
journal = {Scientific Reports},
publisher = {Nature Publishing Group},
year = {2017},
volume = {7},
number = {1},
pages = {3647},
doi = {https://doi.org/10.1038/s41598-017-03920-5}
}
Single-Mode to Multi-Mode Crossover in Thin-Load Polymethyl Methacrylate Plasmonic Waveguides
M. Großmann, M. Thomaschewski, A. Klick, A.J. Goszczak, E.K. Sobolewska, T. Leißner, J. Adam, J. Fiutowski, H.-G. Rubahn and M. Bauer, Plasmonics 2017, 1-8.
Abstract:
Mode character and mode dispersion of sub-60-nm-thick polymethyl methacrylate dielectric-loaded surface plasmon-polariton waveguides (DLSPPWs) are investigated using photoemission electron microscopy and finite element method simulations. Experiment and simulation show excellent agreement and allow identifying a crossover from single-mode to multi-mode waveguiding as a function of excitation wavelength λ and DLSSPW cross section. Experiment and simulations yield, furthermore, indications for the formation of a surface plasmon-polariton cavity mode in the close vicinity of the waveguides.
BibTeX:
@article{Grosmann2017,
author = {Großmann, Malte and Thomaschewski, Martin and Klick, Alwin and Goszczak, Arkadiusz Jarosław and Sobolewska, Elżbieta Karolina and Leißner, Till and Adam, Jost and Fiutowski, Jacek and Rubahn, Horst-Günter and Bauer, Michael},
title = {Single-Mode to Multi-Mode Crossover in Thin-Load Polymethyl Methacrylate Plasmonic Waveguides},
journal = {Plasmonics},
publisher = {Springer},
year = {2017},
pages = {1--8},
doi = {https://doi.org/10.1007/s11468-017-0649-3}
}
Conductance of a free-standing conjugated molecular wire
T. Jasper-Toennies, A. Garcia-Lekue, T. Frederiksen, S. Ulrich, R. Herges and R. Berndt, Phys. Rev. Lett. 2017, 119, 066801.
Abstract:
A free-standing molecular wire is placed vertically on Au(111) using a platform molecule and contacted by a scanning tunneling microscope. Despite the simplicity of the single-molecule junction its conductance G reproducibly varies in a complex manner with the electrode separation. Transport calculations show that G is controlled by a deformation of the molecule, a symmetry mismatch between the tip and molecule orbitals, and the breaking of a C≡C triple in favor of a Au–C–C bond. This tip-controlled reversible bond formation/rupture alters the electronic spectrum of the junction and the states accessible for transport, resulting in an order of magnitude variation of the conductance.
BibTeX:
@article{Jasper-Toennies2017,
author = {Jasper-Toennies, Torben and Garcia-Lekue, Aran and Frederiksen, Thomas and Ulrich, Sandra and Herges, Rainer and Berndt, Richard},
title = {Conductance of a free-standing conjugated molecular wire},
journal = {Phys. Rev. Lett.},
year = {2017},
volume = {119},
pages = {066801}
}
Robust and selective switching of a Fe(III) spin-crossover compound on Cu2N/Cu(100) with memristance behavior
T. Jasper-Toennies, M. Gruber, S. Karan, H. Jacob, F. Tuczek and R. Berndt, Nano Letters 2017, 17, published online.
Abstract:
The switching between two spin states makes spin-crossover molecules on surfaces very attractive for potential applications in molecular spintronics. Using scanning tunneling microscopy, the successful deposition of [Fe(pap)2 ]+ (pap = N-2-pyridylmethylidene-2- hydroxyphenylaminato) molecules on Cu2N/Cu(100) surface is evidenced. The deposited FeIII spin-crossover compound is controllably switched between three different states, each of them exhibiting a characteristic tunneling conductance. The conductance is therefore employed to readily read the state of the molecules. A comparison of the experimental data with the results of density-functional-theory calculations reveals that all Fe(pap)2 molecules are initially in their high-spin state. The two other states are compatible with the low-spin state of the molecule but differ with respect to their coupling to the substrate. As a proof of concept, the reversible and selective nature of the switching is used to build a two-molecule memory.
BibTeX:
@article{Jasper-Toennies0,
author = {Jasper-Toennies, Torben and Gruber, Manuel and Karan, Sujoy and Jacob, Hanne and Tuczek, Felix and Berndt, Richard},
title = {Robust and selective switching of a Fe(III) spin-crossover compound on Cu2N/Cu(100) with memristance behavior},
journal = {Nano Letters},
year = {2017},
volume = {17},
number = {ja},
pages = {published online},
doi = {https://doi.org/10.1021/acs.nanolett.7b02481}
}
High-Frequency Mechanostimulation of Cell Adhesion
L.F. Kadem, K.G. Suana, M. Holz, W. Wang, H. Westerhaus, R. Herges and C. Selhuber-Unkel, Angewandte Chemie International Edition 2017, 56, 225-229.
Abstract:
Cell adhesion is regulated by molecularly defined protein interactions and by mechanical forces, which can activate a dynamic restructuring of adhesion sites. Previous attempts to explore the response of cell adhesion to forces have been limited to applying mechanical stimuli that involve the cytoskeleton. In contrast, we here apply a new, oscillatory type of stimulus through push–pull azobenzenes. Push–pull azobenzenes perform a high-frequency, molecular oscillation upon irradiation with visible light that has frequently been applied in polymer surface relief grating. We here use these oscillations to address single adhesion receptors. The effect of molecular oscillatory forces on cell adhesion has been analyzed using single-cell force spectroscopy and gene expression studies. Our experiments demonstrate a reinforcement of cell adhesion as well as upregulated expression levels of adhesion-associated genes as a result of the nanoscale “tickling” of integrins. This novel type of mechanical stimulus provides a previously unprecedented molecular control of cellular mechanosensing.
BibTeX:
@article{Kadem2017,
author = {Kadem, Laith F and Suana, K Grace and Holz, Michelle and Wang, Wei and Westerhaus, Hannes and Herges, Rainer and Selhuber-Unkel, Christine},
title = {High-Frequency Mechanostimulation of Cell Adhesion},
journal = {Angewandte Chemie International Edition},
publisher = {Wiley Online Library},
year = {2017},
volume = {56},
number = {1},
pages = {225-229},
doi = {https://doi.org/10.1002/anie.201609483}
}
Soft-x-ray-induced spin-state switching of an adsorbed Fe(II) spin-crossover complex
L. Kipgen, M. Bernien, F. Nickel, H. Naggert, A.J. Britton, L.M. Arruda, E. Schierle, E. Weschke, F. Tuczek and W. Kuch, Journal of Physics: Condensed Matter 2017, 29, 394003.
Abstract:
For probing the nature of spin-state switching in spin-crossover molecules adsorbed on surfaces, x-ray absorption spectroscopy has emerged as a powerful tool due to its high sensitivity and element selectivity in tracing even subtle electronic, magnetic, or chemical changes. However, the x-rays itself can induce a spin transition and might have unwanted influence while investigating the effect of other stimuli such as temperature or light, or of the surface, on the spin switching behaviour. Herein, we present the spin switching of an Fe(II) complex adsorbed on a highly oriented pyrolytic graphite surface with particular emphasis on the x-ray-induced switching. For a submonolayer coverage, the complex undergoes a complete and reversible temperature- and light-induced spin transition. The spin states are switched both ways by x-rays at 5 K, i.e. from the high-spin state to the low-spin state or vice versa, depending on the relative amount of each species. Furthermore, we quantify the fraction of molecules undergoing soft x-ray-induced photochemistry, a process which results in an irreversible low-spin state component, for a particular exposure time. This can be greatly suppressed by reducing the beam intensity.
BibTeX:
@article{Kipgen2017,
author = {Lalminthang Kipgen and Matthias Bernien and Fabian Nickel and Holger Naggert and Andrew J Britton and Lucas M Arruda and Enrico Schierle and Eugen Weschke and Felix Tuczek and Wolfgang Kuch},
title = {Soft-x-ray-induced spin-state switching of an adsorbed Fe(II) spin-crossover complex},
journal = {Journal of Physics: Condensed Matter},
publisher = {IOP Publishing},
year = {2017},
volume = {29},
number = {39},
pages = {394003},
doi = {https://doi.org/10.1088/1361-648x/aa7e52}
}
Bioinspired photocontrollable microstructured transport device
E. Kizilkan, J. Strueben, A. Staubitz and S.N. Gorb, Science Robotics 2017, 2, eaak9454.
Abstract:
Geckos, which can walk upside down on vertical and underneath horizontal surfaces, owe this ability to the hierarchical structures under their toes. These structures are responsible for substantial adhesion and, at the same time, for quick detachment by mechanical stimulus through leg movements. Inspired by such stimuli-responsive systems in nature, we developed an artificial, photocontrollable microstructured transport device. Through tunable ultraviolet light illumination, the adhesive ability of this bioinspired transport device is reduced up to a factor of 2.7 in terms of adhesive forces and is quickly recovered when the light stimulus ceases. This bioinspired photocontrollable device has been used in a pick-up and drop-down system for transporting planar and three-dimensional solid objects.
BibTeX:
@article{Kizilkan2017,
author = {Kizilkan, Emre and Strueben, Jan and Staubitz, Anne and Gorb, Stanislav N},
title = {Bioinspired photocontrollable microstructured transport device},
journal = {Science Robotics},
publisher = {Science Robotics},
year = {2017},
volume = {2},
number = {2},
pages = {eaak9454},
doi = {https://doi.org/10.1126/scirobotics.aak9454}
}
Ligand-Induced Energy Shift and Localization of Kondo Resonances in Cobalt-Based Complexes on Cu(111)
T. Knaak, M. Gruber, C. Lindström, M.-L. Bocquet, J. Heck and R. Berndt, Nano Letters 2017, 17, published online.
Abstract:
Magnetic sandwich complexes are of particular interest for molecular spintronics. Using scanning tunneling microscopy, we evidence the successful deposition of 1,3,5-tris-(η6-borabenzene-η5-cyclopentadienylcobalt) benzene, a molecule composed of three connected magnetic sandwich units, on Cu(111). Scanning tunneling spectra reveal two distinct spatial-dependent narrow resonances close to the Fermi level for the trimer molecules as well as for molecular fragments composed of one and two magnetic units. With the help of density functional theory, these resonances are interpreted as two Kondo resonances originating from two distinct non-degenerate d-like orbitals. These Kondo resonances are found to have defined spatial extents dictated by the hybridization of the involved orbitals with that of the ligands. These results opens promising perspectives for investigating complex Kondo systems composed of several “Kondo” orbitals.
BibTeX:
@article{Knaak0,
author = {Knaak, Thomas and Gruber, Manuel and Lindström, Christoph and Bocquet, Marie-Laure and Heck, Jürgen and Berndt, Richard},
title = {Ligand-Induced Energy Shift and Localization of Kondo Resonances in Cobalt-Based Complexes on Cu(111)},
journal = {Nano Letters},
year = {2017},
volume = {17},
number = {ja},
pages = {published online},
doi = {https://doi.org/10.1021/acs.nanolett.7b04181}
}
Solvent-Free Synthesis of Diazocine
W. Moormann, D. Langbehn and R. Herges, Synthesis 2017, 49, 3471-3475.
Abstract:
A convenient two-step synthesis of diazocine starting from 2-nitrotoluene is described. The first step, the oxidative dimerization of 2-nitrotoluene, is improved to 95% yield. The second step, the reductive azo cyclization, is performed as a solvent-free reaction with lead powder in a ball mill (51% yield). As a reference, the previously described azo cyclization with Zn/Ba(OH)2 is investigated in detail. The results explain why in previous experiments the yields are low and extremely dependent on the reaction conditions. In view of potential applications in photopharmacology, we checked the stability under reducing conditions. Diazocine does not react with glutathione, indicating intracellular stability.
BibTeX:
@article{Moormann2017,
author = {Moormann, Widukind and Langbehn, Daniel and Herges, Rainer},
title = {Solvent-Free Synthesis of Diazocine},
journal = {Synthesis},
publisher = {&circledc; Georg Thieme Verlag},
year = {2017},
volume = {49},
number = {15},
pages = {3471-3475},
doi = {https://doi.org/10.1055/s-0036-1590685}
}
Nanostructured Fibrous Membranes with Rose Spike-Like Architecture
A. Nasajpour, S. Mandla, S. Shree, E. Mostafavi, R. Sharifi, A. Khalilpour, S. Saghazadeh, S. Hassan, M.J. Mitchell, J. Leijten, X. Hou, A. Moshaverinia, N. Annabi, R. Adelung, Y.K. Mishra, S.R. Shin, A. Tamayol and A. Khademhosseini, Nano Letters 2017, 17, 6235-6240.
Abstract:
Nanoparticles have been used for engineering composite materials to improve the intrinsic properties and/or add functionalities to pristine polymers. The majority of the studies have focused on the incorporation of spherical nanoparticles within the composite fibers. Herein, we incorporate anisotropic branched-shaped zinc oxide (ZnO) nanoparticles into fibrous scaffolds fabricated by electrospinning. The addition of the branched particles resulted in their protrusion from fibers, mimicking the architecture of a rose stem. We demonstrated that the encapsulation of different-shape particles significantly influences the physicochemical and biological activities of the resultant composite scaffolds. In particular, the branched nanoparticles induced heterogeneous crystallization of the polymeric matrix and enhance the ultimate mechanical strain and strength. Moreover, the three-dimensional (3D) nature of the branched ZnO nanoparticles enhanced adhesion properties of the composite scaffolds to the tissues. In addition, the rose stem-like constructs offered excellent antibacterial activity, while supporting the growth of eukaryote cells.
BibTeX:
@article{Nasajpour2017,
author = {Amir Nasajpour and Serena Mandla and Sindu Shree and Ebrahim Mostafavi and Roholah Sharifi and Akbar Khalilpour and Saghi Saghazadeh and Shabir Hassan and Michael J. Mitchell and Jeroen Leijten and Xu Hou and Alireza Moshaverinia and Nasim Annabi and Rainer Adelung and Yogendra Kumar Mishra and Su Ryon Shin and Ali Tamayol and Ali Khademhosseini},
title = {Nanostructured Fibrous Membranes with Rose Spike-Like Architecture},
journal = {Nano Letters},
publisher = {American Chemical Society (ACS)},
year = {2017},
volume = {17},
number = {10},
pages = {6235--6240},
doi = {https://doi.org/10.1021/acs.nanolett.7b02929}
}
Vacuum-evaporable spin-crossover complexes in direct contact with a solid surface: Bismuth vs. gold
S. Ossinger, H. Naggert, L. Kipgen, T. Jasper-Toennies, J. Rudnik, F. Nickel, L.M. Arruda, M. Bernien, W. Kuch, R. Berndt and F. Tuczek, J. Phys. Chem. C 2017, 121, 1210-1219.
Abstract:
To investigate the ability for spin-state switching of spin-crossover (SCO) complexes adsorbed to solid substrates, the SCO complex [Fe(H2B(pz)2)2(phenme4)] (pz = pyrazole, phenme4 = 3,4,7,8-tetramethyl-1,10-phenanthroline) is prepared. The new complex is investigated by magnetic susceptibility measurements and Mößbauer spectroscopy in the solid state and by temperature-dependent UV/vis spectroscopy in a thin film deposited by physical vapor deposition (PVD) on quartz glass. Thermal- and light-induced SCO is observed in the bulk and the film on glass. Submonolayers of this complex obtained by PVD are studied by temperature-dependent near-edge X-ray absorption fine structure (NEXAFS) on Au(111) as well as Bi(111) and by scanning tunneling microscopy (STM) on Au(111). NEXAFS shows thermal- and light-induced spin-state switching of the complex on Bi(111), however, with a large temperature-independent high-spin fraction (∼50%). On the other hand, combined evidence from NEXAFS and STM indicates that on Au(111) the complex dissociates into [Fe(H2B(pz)2)2] and phenme4. Similar observations are made with the parent complex [Fe(H2B(pz)2)2(phen)], which on Bi(111) stays intact and exhibits thermal-induced as well as light-induced SCO, but on Au(111) dissociates into [Fe(H2B(pz)2)2] and phen.
BibTeX:
@article{Ossinger2016,
author = {Ossinger, S. and Naggert, H. and Kipgen, L. and Jasper-Toennies, T. and Rudnik, J. and Nickel, F. and Arruda, L. M. and Bernien, M. and Kuch, W. and Berndt, R. and Tuczek, F},
title = {Vacuum-evaporable spin-crossover complexes in direct contact with a solid surface: Bismuth vs. gold},
journal = {J. Phys. Chem. C},
year = {2017},
volume = {121},
pages = {1210-1219},
doi = {https://doi.org/10.1021/acs.jpcc.6b10888}
}
Preparation and isolation of isobenzofuran
M.K. Peters and R. Herges, Beilstein Journal of Organic Chemistry 2017, 13, 2659-2662.
Abstract:
The synthesis, isolation and characterization of isobenzofuran are described in this publication. Isobenzofuran is of general interest in synthetic and physical organic chemistry because it is one of the most reactive dienes known. A number of synthetic pathways have been published which all suffer from disadvantages such as low yields and difficult purification. We present a synthetic pathway to prepare isobenzofuran in laboratory scale with high yields, from affordable, commercially available starting materials.
BibTeX:
@article{Peters2017,
author = {Peters, Morten K and Herges, Rainer},
title = {Preparation and isolation of isobenzofuran},
journal = {Beilstein Journal of Organic Chemistry},
publisher = {Beilstein-Institut},
year = {2017},
volume = {13},
number = {1},
pages = {2659-2662},
doi = {https://doi.org/10.3762/bjoc.13.263}
}
Full-Dimensional Excited-State Intramolecular Proton Transfer Dynamics of Salicylic Acid
T. Raeker and B. Hartke, The Journal of Physical Chemistry A 2017, 121, 5967-5977.
Abstract:
Salicylic acid (SAc) and its excited-state intramolecular proton transfer (ESIPT) capabilities have been studied both experimentally and theoretically by static calculations. However, to our knowledge, no radiationless pathway has been proposed so far. Instead, excited-state deactivation was only investigated via fluorescence. Therefore, we will present full-dimensional photodynamics of SAc using the floating-occupation configuration-interaction (FOCI) treatment with single and paired double excitations based on the semiempirical RM1 Hamiltonian. To further clarify mechanistic details, the potential energy surface (PES) is scanned along the proton transfer coordinates in one and two dimensions. The time-evolution of relevant degrees of freedom (DOF), quantum yields and isomer populations are evaluated from 200 surface-hopping trajectories. It was found that a deactivation pathway from the excited state to the ground state is indeed accessible through a conical intersection, via rotation of the carboxyl group. Together with the ESIPT process, this rotation can also interchange the protons of the two (formal) OH groups, which makes the overall dynamics still more complex. Our full-dimensional photodynamics study provides a comprehensive overview of all these entangled steps.
BibTeX:
@article{Raeker2017,
author = {Raeker, Tim and Hartke, Bernd},
title = {Full-Dimensional Excited-State Intramolecular Proton Transfer Dynamics of Salicylic Acid},
journal = {The Journal of Physical Chemistry A},
publisher = {ACS Publications},
year = {2017},
volume = {121},
number = {32},
pages = {5967--5977},
doi = {https://doi.org/10.1021/acs.jpca.7b03261}
}
Ultrafast Electronic Deactivation Dynamics of Xanthosine Monophosphate
K. Röttger, R. Stellmacher, M. Stuhldreier and F. Temps, Molecules 2017, 22, 160.
Abstract:
Ultrafast energy dissipation is a crucial factor for the photostability of DNA and RNA, but even some of the key electronic deactivation pathways in monomeric nucleic acid building stones are still controversial. Here, we report on the excited-state dynamics of the rare nucleotide xanthosine monophosphate as a function of deprotonation state (XMP vs. XMP − ) and excitation wavelength ( λpump= 278–243 nm) by femtosecond time-resolved fluorescence and absorption spectroscopy. We show that the predominating relaxation channel leads to a return of the photo-excited molecules to the electronic ground state in τ∼1 ps. The mechanism likely involves an out-of-plane deformation of the five-membered ring, different from the main electronic deactivation pathways in the canonical purine bases adenine and guanine. The results are discussed in terms of the structural and electronic differences of XMP compared to the canonical nucleotides.
BibTeX:
@article{Roettger2017,
author = {Katharina Röttger and Rebecca Stellmacher and Mayra Stuhldreier and Friedrich Temps},
title = {Ultrafast Electronic Deactivation Dynamics of Xanthosine Monophosphate},
journal = {Molecules},
publisher = {MDPI AG},
year = {2017},
volume = {22},
number = {1},
pages = {160},
doi = {https://doi.org/10.3390/molecules22010160}
}
Light-induced Conductance Switching in Photomechanically Active Carbon Nanotube-Polymer Composites
V. Schneider, O. Polonskyi, T. Strunskus, M. Elbahri and F. Faupel, Scientific Reports 2017, 7, .
Abstract:
Novel, optically responsive devices with a host of potential applications have been demonstrated by coupling carbon nanomaterials with photochromic molecules. For light-induced conductance switching in particular, we have recently shown that carbon nanotube-polymer nanocomposites containing azobenzene are very attractive and provide stable and non-degradable changes in conductivity over time at standard laboratory conditions. In these composites, the photoswitching mechanisms are based on light-induced changes in electronic properties and related to the Pool-Frenkel conduction mechanism. However, no link between conductivity switching and the molecular motion of azobenzene chromophores could be found due to application of high elastic modulus polymer matrices. Here we report on single wall carbon nanotube-polymer nanocomposites with a soft polycaprolactone polymer host. Such a system clearly shows the transfer of light-induced, nano-sized molecular motion to macroscopic thickness changes of the composite matrix. We demonstrate that these photomechanical effects can indeed overshadow the electronic effects in conductivity switching behavior and lead to a reversion of the conductivity switching direction near the percolation threshold.
BibTeX:
@article{Schneider2017,
author = {V. Schneider and O. Polonskyi and T. Strunskus and M. Elbahri and F. Faupel},
title = {Light-induced Conductance Switching in Photomechanically Active Carbon Nanotube-Polymer Composites},
journal = {Scientific Reports},
publisher = {Springer Nature},
year = {2017},
volume = {7},
number = {1},
doi = {https://doi.org/10.1038/s41598-017-10211-6}
}
Diversely halogenated spiropyrans - Useful synthetic building blocks for a versatile class of molecular switches
M. Schulz-Senft, P.J. Gates, F.D. Sönnichsen and A. Staubitz, Dyes and Pigments 2017, 136, 292-301.
Abstract:
Spiropyrans are dyes that can be reversibly switched to a highly colored merocyanine form by a number of stimuli such as light, mechanical force or temperature. To make use of these molecules, there is a requirement to functionalize them appropriately. Herein we report a library of spiropyrans bearing two (pseudo) halide functional groups on either half of the molecule. Such halide substituents are valuable, because they themselves may be used as reactive sites in cross-coupling reactions, for example. Different combinations of halides, for which different reactivities in cross-coupling reactions may be expected, will facilitate selective consecutive cross-coupling reactions and condensations. Data concerning the UV/vis characteristics, the photostationary equilibria of the materials as well as the half-life of the merocyanine forms in solution are presented.
BibTeX:
@article{Schulz-Senft2017,
author = {Mathias Schulz-Senft and Paul J. Gates and Frank D. Sönnichsen and Anne Staubitz},
title = {Diversely halogenated spiropyrans - Useful synthetic building blocks for a versatile class of molecular switches},
journal = {Dyes and Pigments},
publisher = {Elsevier BV},
year = {2017},
volume = {136},
pages = {292--301},
doi = {https://doi.org/10.1016/j.dyepig.2016.08.039}
}
Light, Force, and Heat: A Multi-Stimuli Composite that Reveals its Violent Past
S. Shree, M. Schulz-Senft, N.H. Alsleben, Y.K. Mishra, A. Staubitz and R. Adelung, ACS Applied Materials & Interfaces 2017, 9, 38000-38007.
Abstract:
A self-reporting polythiourethane/tetrapodal-ZnO (PTU/T-ZnO) composite is produced using spiropyran as an additive at a concentration as low as 0.5 wt %. Exposure to heat, UV light and mechanical force caused the spiropyran to undergo reversible isomerization indicated by a reversible color change. The studies have been conducted with a constant spiropyran concentration at 0.5 wt %, meanwhile varying the T-ZnO concentration from 0 to 7.5 wt %. The tetrapodal ZnO served as a prism: the light scattering effect of T-ZnO created a visual impression of uniform color distribution. The interconnected network of the tetrapodal of ZnO embedded in the PTU matrix enhanced the mechanical stability of the polymer leading to high impact resistance up to ∼232 kPa. PTU/spiropyran also emerged as a possible thermal sensing coating, due to its temperature sensitivity. Due to the broad green luminescence band (∼535 nm) in T-ZnO, the colored merocyanine form which absorbs in this region of the spectrum switches back to spiropyran at this wavelength. High concentrations of T-ZnO were shown to reduce the effect one of the switching triggers i.e., ultraviolet light. Using this property of T-ZnO it was possible to achieve a switchable system with the possibility of separating the stimuli.
BibTeX:
@article{Shree2017,
author = {Sindu Shree and Mathias Schulz-Senft and Nils H. Alsleben and Yogendra Kumar Mishra and Anne Staubitz and Rainer Adelung},
title = {Light, Force, and Heat: A Multi-Stimuli Composite that Reveals its Violent Past},
journal = {ACS Applied Materials & Interfaces},
publisher = {American Chemical Society (ACS)},
year = {2017},
volume = {9},
number = {43},
pages = {38000--38007},
doi = {https://doi.org/10.1021/acsami.7b09598}
}
Ultrafast dynamics of UV-excited trans- and cis-ferulic acid in aqueous solutions
S. Wang, S. Schatz, M.C. Stuhldreier, H. Böhnke, J. Wiese, C. Schröder, T. Raeker, B. Hartke, J.K. Keppler, K. Schwarz, F. Renth and F. Temps, Physical Chemistry Chemical Physics 2017, 19, 30683-30694.
Abstract:
The ultrafast UV-induced processes of the neutral, anionic and dianionic forms of trans- and cis-ferulic acid (FA) in aqueous solution were studied by static and femtosecond time-resolved emission and absorption spectroscopy combined with quantum chemical calculations. In all cases, initial excitation populates the first 1ππ* state. For the dianionic cis-isomer cFA2−, electronic deactivation takes place with a time constant of only 1.4 ps, whereas in all other cases, excited-state deactivation happens more than ten times slower, on a time scale of ≈20 ps. The data suggest sequential de-excitation pathways, where initial sub-picosecond solvent rearrangement and structural changes are followed by internal conversion to an intermediate excited electronic state from which deactivation to the ground state proceeds. Considering the time scales, barrierless excited-state pathways are suggested only in the case of cFA2−, where the observed formation of the isomerisation photoproduct tFA2− provides clear evidence for a cis ⇄ trans isomerisation coordinate. In the other cases, pathways with an excited-state energy barrier, presumably along the same coordinate, are likely, given the longer excited-state lifetimes.
BibTeX:
@article{Wang2017,
author = {Shuangqing Wang and Sebastian Schatz and Mayra C. Stuhldreier and Hendrik Böhnke and Joss Wiese and Carsten Schröder and Tim Raeker and Bernd Hartke and Julia K. Keppler and Karin Schwarz and Falk Renth and Friedrich Temps},
title = {Ultrafast dynamics of UV-excited trans- and cis-ferulic acid in aqueous solutions},
journal = {Physical Chemistry Chemical Physics},
publisher = {Royal Society of Chemistry (RSC)},
year = {2017},
volume = {19},
number = {45},
pages = {30683--30694},
doi = {https://doi.org/10.1039/c7cp05301k}
}
13-cis retinoic acid on coinage metals: Hierarchical self-assembly and spin generation
X. Zhang, N. Li, Y. Zhang, R. Berndt and Y. Wang, Physical Chemistry Chemical Physics 2017, 19, 14919.
Abstract:
Hierarchical self-assembly of 13-cis-retinoic acid on Au(111) and Ag(111) was investigated using low-temperature scanning tunnelling microscopy. On both surfaces, molecules form dimers by hydrogen bonds and the dimers arrange into ordered two-dimensional arrays through van der Waals forces. Three packing modes are observed on Au(111) and only one on Ag(111). We tentatively attribute the different patterns on the two surfaces to a stronger molecule–substrate interaction on Ag(111) and site-dependent molecular adsorption on different atomic lattices. In addition, 13-cis-ReA on Au(111) can be made to carry a localized spin.
BibTeX:
@article{Zhang2017a,
author = {Zhang, Xue and Li, Na and Zhang, Yajie and Berndt, Richard and Wang, Yongfeng},
title = {13-cis retinoic acid on coinage metals: Hierarchical self-assembly and spin generation},
journal = {Physical Chemistry Chemical Physics},
publisher = {Royal Society of Chemistry},
year = {2017},
volume = {19},
pages = {14919},
doi = {https://doi.org/10.1039/c7cp01568b}
}
Mechanochemistry induced with a robust functionalized tip
Y. Zhang, Y. Wang, J.-T. Lu, M. Brandbyge and R. Berndt, Angew. Chem. 2017, 129, 11931 –11935.
Abstract:
Atomic-scale mechanochemistry is realized from force exerted by a C60 -functionalized scanning tunneling microscope tip. Two conformers of tin phthalocyanine can be prepared on coinage metal surfaces. A transition between these conformers is induced on Cu(111) and Ag(100). Density functional theory calculations reveal details of this reaction. Because of the large energy barrier of the reaction and the strong interaction of SnPc with Cu(111), the process can not be achieved by electrical means.
BibTeX:
@article{Zhang2017,
author = {Yajie Zhang and Yongfeng Wang and Jing-Tao Lu and Mads Brandbyge and Richard Berndt},
title = {Mechanochemistry induced with a robust functionalized tip},
journal = {Angew. Chem.},
year = {2017},
volume = {129},
pages = {11931 –11935},
doi = {https://doi.org/10.1002/ange.201704940}
}
On-Surface Synthesis of Heptacene and its Interaction with a Metal Surface
M. Zugermeier, M. Gruber, M. Schmid, B. Klein, L. Ruppenthal, P. Müller, R. Einholz, W. Hieringer, R. Berndt, H.F. Bettinger and others, Nanoscale 2017, 9, 12461.
Abstract:
Heptacene was generated by surface-assisted didecarbonylation of an α-diketone precursor on a Ag(111) surface. Monitoring of the surface reaction and characterization of the adsorbed heptacene was performed with scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT) calculations. The surface-assisted formation of heptacene occurs around 460 K. Both the heptacene and the precursor molecules are oriented along the high-symmetry directions of the (111) surface and their molecular π systems face towards the substrate. The interaction with the Ag(111) substrate is not laterally uniform, but appears to be strongest on the central part of the molecule, in line with the expectations from Clar’s rule. In the STM images, heptacene shows a dumbbell shape, which may correspond to the substantial out-of-plane deformations of heptacene on Ag(111). As revealed by DFT, the center of the molecule is closer to the surface than the outer parts. In addition, the inner rings are most affected by charge redistribution between surface and molecule. Heptacene acts as an acceptor and receives a negative charge of −0.6e from the Ag(111) surface. Since vacuum-sublimable α-diketone precursors for even larger acenes are available, the approach is promising for the on-surface synthesis of higher acene homologues such as octacene and nonacene.
BibTeX:
@article{Zugermeier2017,
author = {Zugermeier, Malte and Gruber, Manuel and Schmid, Martin and Klein, Benedikt and Ruppenthal, Lukas and Müller, Philipp and Einholz, Ralf and Hieringer, Wolfgang and Berndt, Richard and Bettinger, Holger F and others},
title = {On-Surface Synthesis of Heptacene and its Interaction with a Metal Surface},
journal = {Nanoscale},
publisher = {Royal Society of Chemistry},
year = {2017},
volume = {9},
pages = {12461},
doi = {https://doi.org/10.1039/c7nr04157h}
}
Manipulation of Cyclohexene-Based Organic Molecules on Various Metallic Substrates
M. Gruber and R. Berndt, J. Phys. Chem. C 2016, 18642–18650.
Abstract:
Shikimic-acid and beta-carotene molecules were investigated on various metallic substrates using scanning tunneling microscopy at ∼5 K. We studied the potential ability of these metal-free organic molecules to be switched into a magnetic state as it was recently evidenced for retinoic acid and cholesterol on Au(111). While our attempts to generate spin within shikimic-acid and beta-carotene molecules proved unsuccessful, switching attempts for different molecule/substrate pairs were thoroughly analyzed so as to tentatively elucidate the underlying causes of the vain attempts. We speculate that, by avoiding the identified causes, other organic molecule/substrate pairs can be found for spin manipulation.
BibTeX:
@article{Gruber2016,
author = {Manuel Gruber and Richard Berndt},
title = {Manipulation of Cyclohexene-Based Organic Molecules on Various Metallic Substrates},
journal = {J. Phys. Chem. C},
publisher = {American Chemical Society (ACS)},
year = {2016},
pages = {18642–18650},
doi = {https://doi.org/10.1021/acs.jpcc.6b06089}
}
Imine-Functionalized Triazatriangulenium Platforms: Towards an Artificial Ciliated Epithelium
M. Hammerich, T. Rusch, N.R. Krekiehn, A. Bloedorn, O.M. Magnussen and R. Herges, ChemPhysChem 2016, 17, 1870-1874.
Abstract:
Triazatriangulenium (TATA) platforms have been used to prepare highly ordered, self-assembled monolayers of free- and vertically standing imines on Au(111) surfaces. Upon irradiation, the imines undergo trans–cis isomerization and a fast thermal reaction (t1/2=0.58 s at 20 °C) back to the more stable trans form. It is known that the photochemical reaction proceeds through rotation of the C=N bond and the thermochemical reaction through inversion at the N atom. The imine motors, therefore, should be able to induce a net displacement of particles above the surface similar to cilia epithelia in nature.
BibTeX:
@article{Hammerich2016,
author = {Melanie Hammerich and Talina Rusch and Nicolai R. Krekiehn and Andreas Bloedorn and Olaf M. Magnussen and Rainer Herges},
title = {Imine-Functionalized Triazatriangulenium Platforms: Towards an Artificial Ciliated Epithelium},
journal = {ChemPhysChem},
publisher = {Wiley-Blackwell},
year = {2016},
volume = {17},
number = {12},
pages = {1870--1874},
doi = {https://doi.org/10.1002/cphc.201600147}
}
Heterodiazocines: Synthesis and Photochromic Properties, Trans to Cis Switching within the Bio-optical Window
M. Hammerich, C. Schütt, C. Stähler, P. Lentes, F. Röhricht, R. Höppner and R. Herges, Journal of the American Chemical Society 2016, 138, 13111-13114.
Abstract:
Diazocines, bridged azobenzenes, exhibit superior photophysical properties compared to parent azobenzenes such as high switching efficiencies, quantum yields, and particularly switching wavelengths in the visible range. Synthesis, however, proceeds with low yields, and derivatives are difficult to prepare. We now present two heterodiazocines which are easier to synthesize, and the general procedures should also provide facile access to derivatives. Moreover, both compounds can be switched with light in the far-red (650 nm). Accessibility and photophysical properties make them ideal candidates for applications such as photoswitchable drugs and functional materials.
BibTeX:
@article{Hammerich2016a,
author = {Hammerich, Melanie and Schütt, Christian and Stähler, Cosima and Lentes, Pascal and Röhricht, Fynn and Höppner, Ronja and Herges, Rainer},
title = {Heterodiazocines: Synthesis and Photochromic Properties, Trans to Cis Switching within the Bio-optical Window},
journal = {Journal of the American Chemical Society},
publisher = {ACS Publications},
year = {2016},
volume = {138},
number = {40},
pages = {13111--13114},
doi = {https://doi.org/10.1021/jacs.6b05846}
}
AFM Imaging of Mercaptobenzoic Acid on Au(110): Sub-Molecular Contrast with Metal Tips
N. Hauptmann, R. Robles, P. Abufager, N. Lorente and R. Berndt, J. Phys. Chem. Lett. 2016, 7, 1984−1990.
Abstract:
A self-assembled monolayer of mercaptobenzoic acid (MBA) on Au(110) is investigated with scanning tunneling and atomic force microscopy (STM, AFM) and density functional calculations. High-resolution AFM images obtained with metallic tips show clear contrasts between oxygen atoms and phenyl moieties. The contrast above the oxygen atoms is due to attractive covalent interactions which is different from previously reported high-resolution images where Pauli repulsion dominated the image contrast. We show that the bonding of MBA to the substrate occurs mainly through dispersion interactions while the thiol-Au bond contributes only a quarter of the adsorption energy. No indication of Au adatoms mediating the thiol-Au interaction was found in contrast to other thiol-bonded systems. However, MBA lifts the Au(110)-(2 x 1) reconstruction.
BibTeX:
@article{Hauptmann2016,
author = {Nadine Hauptmann and Roberto Robles and Paula Abufager and Nicolas Lorente and Richard Berndt},
title = {AFM Imaging of Mercaptobenzoic Acid on Au(110): Sub-Molecular Contrast with Metal Tips},
journal = {J. Phys. Chem. Lett.},
publisher = {American Chemical Society (ACS)},
year = {2016},
volume = {7},
pages = {1984−1990},
doi = {https://doi.org/10.1021/acs.jpclett.6b00684}
}
Broadband Anti-Reflective Coating Based on Plasmonic Nanocomposite
M.K. Hedayati, M. Abdelaziz, C. Etrich, S. Homaeigohar, C. Rockstuhl and M. Elbahri, Materials 2016, 9, 636.
Abstract:
We report on the fabrication, the characterization, and the optical simulation of a gold–silica nanocomposite and present its integration into a broadband anti-reflective coating (ARC) for a silicon substrate. The two-layer ARC consists of a nanocomposite (randomly distributed gold cluster in a silica matrix) and a pure silica film. We capitalize on the large refractive index of the composite to impose an abrupt phase change at the interface of the coating to diminish the light reflection from the substrate through the ultrathin nanocoating. The average reflectivity of the silicon can be reduced by such a coating to less than 0.1% in the entire visible spectrum. We experimentally and numerically prove that percolated nanocomposites with an overall thickness of 20 nm can provide anti-reflectivity up to near infrared (NIR). The ARC bandwidth can be shifted more than 500 nm and broadened to cover even the NIR wavelength by changing the volume filling fraction of the gold clusters. The angular sensitivity of thin ultrathin antireflective coating is negligible up to 60°. The present ARC could find applications in thermo-photovoltaics and bolometers.
BibTeX:
@article{Hedayati2016a,
author = {Mehdi Keshavarz Hedayati and Moheb Abdelaziz and Christoph Etrich and Shahin Homaeigohar and Carsten Rockstuhl and Mady Elbahri},
title = {Broadband Anti-Reflective Coating Based on Plasmonic Nanocomposite},
journal = {Materials},
publisher = {MDPI AG},
year = {2016},
volume = {9},
number = {8},
pages = {636},
doi = {https://doi.org/10.3390/ma9080636}
}
Antireflective Coatings: Conventional Stacking Layers and Ultrathin Plasmonic Metasurfaces, A Mini-Review
M.K. Hedayati and M. Elbahri, Materials 2016, 9, 497.
Abstract:
Reduction of unwanted light reflection from a surface of a substance is very essential for improvement of the performance of optical and photonic devices. Antireflective coatings (ARCs) made of single or stacking layers of dielectrics, nano/microstructures or a mixture of both are the conventional design geometry for suppression of reflection. Recent progress in theoretical nanophotonics and nanofabrication has enabled more flexibility in design and fabrication of miniaturized coatings which has in turn advanced the field of ARCs considerably. In particular, the emergence of plasmonic and metasurfaces allows for the realization of broadband and angular-insensitive ARC coatings at an order of magnitude thinner than the operational wavelengths. In this review, a short overview of the development of ARCs, with particular attention paid to the state-of-the-art plasmonic- and metasurface-based antireflective surfaces, is presented.
BibTeX:
@article{Hedayati2016,
author = {Mehdi Keshavarz Hedayati and Mady Elbahri},
title = {Antireflective Coatings: Conventional Stacking Layers and Ultrathin Plasmonic Metasurfaces, A Mini-Review},
journal = {Materials},
publisher = {MDPI AG},
year = {2016},
volume = {9},
number = {6},
pages = {497},
doi = {https://doi.org/10.3390/ma9060497}
}
Modular Synthetic Route to Monofunctionalized Porphyrin Architectures
G. Heitmann, M. Dommaschk, R. Löw and R. Herges, Organic Letters 2016, 18, 5228-5231.
Abstract:
The synthesis of a borylated Ni2+ porphyrin and its application as a versatile precursor for building up functional ortho-substituted tetraaryl porphyrin architectures is reported. This precursor porphyrin provides the basis for efficient modular syntheses of porphyrin compounds with covalently attached axial ligands which are important as enzyme model complexes, electron transfer dyads, and many other applications. In the present study, the precursor porphyrin was used for the synthesis of molecular spin switches which previously showed high potential as photoresponsive contrast agents for magnetic resonance imaging.
BibTeX:
@article{Heitmann2016b,
author = {Heitmann, Gernot and Dommaschk, Marcel and Löw, Roland and Herges, Rainer},
title = {Modular Synthetic Route to Monofunctionalized Porphyrin Architectures},
journal = {Organic Letters},
publisher = {ACS Publications},
year = {2016},
volume = {18},
number = {20},
pages = {5228--5231},
doi = {https://doi.org/10.1021/acs.orglett.6b02507}
}
Azoimidazole functionalized Ni-porphyrins for molecular spin switching and light responsive MRI contrast agents
G. Heitmann, C. Schütt, J. Gröbner, L. Huber and R. Herges, Dalton Trans. 2016, 45, 11407-11412.
Abstract:
Azo-N-methylimidazole functionalized Ni(II)porphyrins were rationally designed and synthesized and their performance as molecular spin switches was investigated. They perform intramolecular light-driven coordination-induced spin state switching (LD-CISSS) in the presence of water and therefore are an important step towards spin switches for medicinal applications, particularly functional MRI contrast agents.
BibTeX:
@article{Heitmann2016,
author = {Gernot Heitmann and Christian Schütt and Jens Gröbner and Lukas Huber and Rainer Herges},
title = {Azoimidazole functionalized Ni-porphyrins for molecular spin switching and light responsive MRI contrast agents},
journal = {Dalton Trans.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2016},
volume = {45},
number = {28},
pages = {11407--11412},
doi = {https://doi.org/10.1039/c6dt01727d}
}
Spin State Switching in Solution with an Azoimidazole-Functionalized Nickel(II)-Porphyrin
G. Heitmann, C. Schütt and R. Herges, European Journal of Organic Chemistry 2016, 2016, 3817-3823.
Abstract:
We herein report the synthesis and switching properties of an azo-1-methylimidazole-functionalized Ni2+ porphyrin. Upon irradiation and cis/trans isomerization of the azo unit, 1-methylimidazole is reversibly coordinated as an axial ligand to the Ni2+ porphyrin. Consequently, the Ni2+ is switched between a diamagnetic low-spin state (trans) and a paramagnetic high-spin state (cis) according to the light-driven coordination-induced spin state switching (LD-CISSS) principle. The spin state switching is operable in solution under ambient conditions. The paramagnetic cis-species is formed in exceptionally high amounts upon irradiation with UV light (365 nm), whereas an excess of the diamagnetic trans-species was obtained upon irradiation with blue light (430 nm).
BibTeX:
@article{Heitmann2016a,
author = {Gernot Heitmann and Christian Schütt and Rainer Herges},
title = {Spin State Switching in Solution with an Azoimidazole-Functionalized Nickel(II)-Porphyrin},
journal = {European Journal of Organic Chemistry},
publisher = {Wiley-Blackwell},
year = {2016},
volume = {2016},
number = {22},
pages = {3817--3823},
doi = {https://doi.org/10.1002/ejoc.201600548}
}
Vacuum synthesis of magnetic aluminum phthalocyanine on Au(111)
I.-P. Hong, N. Li, Y.-J. Zhang, H. Wang, H.-J. Song, M.-L. Bai, X. Zhou, J.-L. Li, G.-C. Gu, X. Zhang, M. Chen, J.M. Gottfried, D. Wang, J.-T. Lü, L.-M. Peng, S.-M. Hou, R. Berndt, K. Wu and Y.-F. Wang, Chem. Commun. 2016, 52, 10338-10341.
Abstract:
Air-unstable magnetic aluminum phthalocyanine (AlPc) molecules are prepared by an on-surface metalation reaction of phthalocyanine with aluminum (Al) atoms on Au(111) in ultrahigh vacuum. Experiments and density functional theory calculations show that an unpaired spin is located on the conjugated isoindole lobes of the molecule rather than at the Al position.
BibTeX:
@article{Hong2016,
author = {I-Po Hong and Na Li and Ya-Jie Zhang and Hao Wang and Huan-Jun Song and Mei-Lin Bai and Xiong Zhou and Jian-Long Li and Gao-Chen Gu and Xue Zhang and Min Chen and J. Michael Gottfried and Dong Wang and Jing-Tao Lü and Lian-Mao Peng and Shi-Min Hou and Richard Berndt and Kai Wu and Yong-Feng Wang},
title = {Vacuum synthesis of magnetic aluminum phthalocyanine on Au(111)},
journal = {Chem. Commun.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2016},
volume = {52},
number = {68},
pages = {10338--10341},
doi = {https://doi.org/10.1039/c6cc03359h}
}
Generation of spin in single cholesterol molecules on gold
S. Karan and R. Berndt, Phys. Chem. Chem. Phys. 2016, 18, 9334-9337.
Abstract:
Compact islands of cholesterol on Au(111) were investigated with scanning tunneling microscopy at B5 K. Single molecules have been switched among several states, three of which exhibit a sharp spectroscopic feature at the Fermi level. This feature signals the presence of a localized spin and suggests that the molecule may be controllably switched between paramagnetic and diamagnetic states.
BibTeX:
@article{Karan2016,
author = {Sujoy Karan and Richard Berndt},
title = {Generation of spin in single cholesterol molecules on gold},
journal = {Phys. Chem. Chem. Phys.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2016},
volume = {18},
number = {14},
pages = {9334--9337},
doi = {https://doi.org/10.1039/c5cp07410j}
}
Spin Manipulation by Creation of Single-Molecule Radical Cations
S. Karan, N. Li, Y. Zhang, Y. He, I.-P. Hong, H. Song, J.-T. Lü, Y. Wang, L. Peng, K. Wu, G.S. Michelitsch, R.J. Maurer, K. Diller, K. Reuter, A. Weismann and R. Berndt, Phys. Rev. Lett. 2016, 116, 027201.
Abstract:
All-trans-retinoic acid (ReA), a closed-shell organic molecule comprising only C, H, and O atoms, is investigated on a Au(111) substrate using scanning tunneling microscopy and spectroscopy. In dense arrays single ReA molecules are switched to a number of states, three of which carry a localized spin as evidenced by conductance spectroscopy in high magnetic fields. The spin of a single molecule may be reversibly switched on and off without affecting its neighbors. We suggest that ReA on Au is readily converted to a radical by the abstraction of an electron.
BibTeX:
@article{KaranLiZhangEtAl2016,
author = {Karan, Sujoy and Li, Na and Zhang, Yajie and He, Yang and Hong, I-Po and Song, Huanjun and Lü, Jing-Tao and Wang, Yongfeng and Peng, Lianmao and Wu, Kai and Michelitsch, Georg S. and Maurer, Reinhard J. and Diller, Katharina and Reuter, Karsten and Weismann, Alexander and Berndt, Richard},
title = {Spin Manipulation by Creation of Single-Molecule Radical Cations},
journal = {Phys. Rev. Lett.},
publisher = {American Physical Society},
year = {2016},
volume = {116},
pages = {027201},
doi = {https://doi.org/10.1103/PhysRevLett.116.027201}
}
Influence of the porosity on the photoresponse of a liquid crystal elastomer
E. Kizilkan, J. Strueben, X. Jin, C.F. Schaber, R. Adelung, A. Staubitz and S.N. Gorb, R. Soc. open sci. 2016, 3, 150700.
Abstract:
Azobenzene containing liquid crystal elastomers (LCEs) are among of the most prominent photoresponsive polymers due to their fast and reversible response to different light stimuli. To bring new functions into the present framework, novel modifications in bulk material morphology are required. Therefore, we produced azobenzene LCE free-standing films with different porosities. While the porosity provided macroscopic morphological changes, at the same time, it induced modifications in alignment of liquid crystal azobenzene units in the films. We found that a high porosity increased the photoresponse of the LCE in terms of bending angle with high significance. Moreover, the porous LCE films showed similar bending forces to those of pore-free LCE films.
BibTeX:
@article{Kizilkan2016,
author = {Emre Kizilkan and Jan Strueben and Xin Jin and Clemens F. Schaber and Rainer Adelung and Anne Staubitz and Stanislav N. Gorb},
title = {Influence of the porosity on the photoresponse of a liquid crystal elastomer},
journal = {R. Soc. open sci.},
publisher = {The Royal Society},
year = {2016},
volume = {3},
number = {4},
pages = {150700},
doi = {https://doi.org/10.1098/rsos.150700}
}
6-Methyl-2-[(6-methylpyridin-2-yl)amino]pyridinium chloride chloroform monosolvate
M. Klass, C. Näther and F. Tuczek, IUCrData 2016, 1, .
Abstract:
In the title solvated mol­ecular salt, C12H14N3+·Cl-·CHCl3, the aromatic rings of the cation are nearly coplanar [dihedral angle = 6.30 (5)°] and an intra­molecular N-H...N hydrogen bond occurs. In the crystal, the chloride ion accepts an N-H...Cl hydrogen bond from the cation and a C-H...Cl inter­action from the solvent mol­ecule. These trimeric units are linked by cation-to-anion C-H...Cl inter­actions into chains that propagate in the [001] direction.
BibTeX:
@article{Klass2016,
author = {Michaela Klass and Christian Näther and Felix Tuczek},
title = {6-Methyl-2-[(6-methylpyridin-2-yl)amino]pyridinium chloride chloroform monosolvate},
journal = {IUCrData},
publisher = {International Union of Crystallography (IUCr)},
year = {2016},
volume = {1},
number = {1},
doi = {https://doi.org/10.1107/s2414314615024670}
}
SurfacecisEffect: Influence of an Axial Ligand on Molecular Self-Assembly
T. Knaak, T.G. Gopakumar, B. Schwager, F. Tuczek, R. Robles, N. Lorente and R. Berndt, J. Am. Chem. Soc. 2016, 138, 7544-7550.
Abstract:
Adding ligands to molecules can have drastic and unforeseen consequences in the final products of a reaction. Recently a surface trans effect due to the weakening of a molecule–surface bond was reported. Here, we show a surface cis effect where an axial ligand at adsorbed transition-metal complexes enables lateral bonding among the molecules. In the absence of this ligand, the intermolecular interaction is repulsive and supramolecular patterns are not observed. Fe-tetramethyl-tetraazaannulene on Au(111) was investigated using low-temperature scanning tunneling microscopy and spectroscopy along with density functional theory calculations. At low coverages, the molecules remain isolated. Exposure to CO leads to axial CO bonding and induces reordering into extended clusters of chiral molecular trimers. The changed self-assembly pattern is due to a CO-induced modification of the molecular structure and the corresponding charge transfer between the molecule and the substrate, which in turn changes the lateral intermolecular forces.
BibTeX:
@article{Knaak2016a,
author = {Thomas Knaak and Thiruvancheril G. Gopakumar and Bettina Schwager and Felix Tuczek and Roberto Robles and Nicolás Lorente and Richard Berndt},
title = {SurfacecisEffect: Influence of an Axial Ligand on Molecular Self-Assembly},
journal = {J. Am. Chem. Soc.},
publisher = {American Chemical Society (ACS)},
year = {2016},
volume = {138},
number = {24},
pages = {7544--7550},
doi = {https://doi.org/10.1021/jacs.6b03710}
}
Femtosecond Time-Resolved Dynamics of trans -Azobenzene on Gold Nanoparticles
A. Köhntopp, M. Dittner and F. Temps, J. Phys. Chem. Lett. 2016, 7, 1088-1095.
Abstract:
We report a first femtosecond time-resolved transient absorption study of the photoinduced ultrafast dynamics of trans-azobenzene (AB) on gold nanoparticles (AuNPs). The observed changes in optical density following excitation at λ = 357 nm were analyzed by using temperature-dependent Mie theory and by Lorentzian band fitting to disentangle the ultrafast relaxation of the local surface plasmon resonance (LSPR) excitation of the Au core and the electronic deactivation of the attached AB ligands. The analysis of the dynamics associated with the AB photochrome yielded lifetime constants of τ1 = 1.2 ± 0.2 ps and τ2 = 4.7 ± 1.1 ps. Both values together indicate surprisingly little difference in the dynamics of the AB ligand on the AuNPs vs in solution. Our results thus highlight the extraordinarily efficient electronic decoupling of the azo chromophore and the Au core by the alkyl linker chain.
BibTeX:
@article{Koehntopp2016,
author = {Anja Köhntopp and Mark Dittner and Friedrich Temps},
title = {Femtosecond Time-Resolved Dynamics of trans -Azobenzene on Gold Nanoparticles},
journal = {J. Phys. Chem. Lett.},
publisher = {American Chemical Society (ACS)},
year = {2016},
volume = {7},
number = {7},
pages = {1088--1095},
doi = {https://doi.org/10.1021/acs.jpclett.6b00102}
}
Charging single Co atoms on ultrathin NaCl films
N. Li, H. Wang, D.-L. Song, C. Li, R. Li, S.-M. Hou, Y.-F. Wang and R. Berndt, Dalton Transactions 2016, 45, 16566-16569.
Abstract:
Single Co adatoms adsorbed on a double-layer NaCl film supported by Cu(111) were negatively charged after applying a positive voltage pulse to the sample in a scanning tunnelling microscope. Density functional calculations showed that the magnetic moment of Co changed from 3μB to 2.2μB after charge state manipulation.
BibTeX:
@article{Li2016,
author = {Li, Na and Wang, Hao and Song, Dao-Liang and Li, Chao and Li, Ruoning and Hou, Shi-Min and Wang, Yong-Feng and Berndt, Richard},
title = {Charging single Co atoms on ultrathin NaCl films},
journal = {Dalton Transactions},
publisher = {Royal Society of Chemistry},
year = {2016},
volume = {45},
number = {42},
pages = {16566--16569},
doi = {https://doi.org/10.1039/c6dt01963c}
}
Synthesis of Hetero-bifunctional Azobenzene Glycoconjugates for Bioorthogonal Cross-Linking of Proteins
A. Müller and T.K. Lindhorst, European Journal of Organic Chemistry 2016, 2016, 1669-1672.
Abstract:
Modification of proteins with azobenzene derivatives allows their form and function to be controlled by photochemical E/Z isomerization of the azobenzene N=N bond. Because azobenzene glycoconjugates (ABGs) are particularly promising cross-linkers for the modification of peptides and proteins, we advanced the collection of so far known homo-bifunctional ABGs with the synthesis of hitherto unknown hetero-bifunctionalized ABGs. Alkyne and alkene, alkyne and sulfhydryl, and azido and alkene functions were combined in one molecule to serve as bioorthogonal reaction pairs. With this, access to a multitude of photosensitive proteins is provided.
BibTeX:
@article{Mueller2016,
author = {Anne Müller and Thisbe K. Lindhorst},
title = {Synthesis of Hetero-bifunctional Azobenzene Glycoconjugates for Bioorthogonal Cross-Linking of Proteins},
journal = {European Journal of Organic Chemistry},
publisher = {Wiley-Blackwell},
year = {2016},
volume = {2016},
number = {9},
pages = {1669--1672},
doi = {https://doi.org/10.1002/ejoc.201600136}
}
reax FF Reactive Force Field for Disulfide Mechanochemistry, Fitted to Multireference ab Initio Data
J. Müller and B. Hartke, J. Chem. Theory Comput. 2016, 12, 3913-3925.
Abstract:
Mechanochemistry, in particular in the form of single-molecule atomic force microscopy experiments, is difficult to model theoretically, for two reasons: Covalent bond breaking is not captured accurately by single-determinant, single-reference quantum chemistry methods, and experimental times of milliseconds or longer are hard to simulate with any approach. Reactive force fields have the potential to alleviate both problems, as demonstrated in this work: Using nondeterministic global parameter optimization by evolutionary algorithms, we have fitted a reaxFF force field to high-level multireference ab initio data for disulfides. The resulting force field can be used to reliably model large, multifunctional mechanochemistry units with disulfide bonds as designed breaking points. Explorative calculations show that a significant part of the time scale gap between AFM experiments and dynamical simulations can be bridged with this approach.
BibTeX:
@article{Mueller2016a,
author = {Julian Müller and Bernd Hartke},
title = {reax FF Reactive Force Field for Disulfide Mechanochemistry, Fitted to Multireference ab Initio Data},
journal = {J. Chem. Theory Comput.},
publisher = {American Chemical Society (ACS)},
year = {2016},
volume = {12},
number = {8},
pages = {3913--3925},
doi = {https://doi.org/10.1021/acs.jctc.6b00461}
}
Bis[dihydrobis(pyrazol-1-yl-upkappaN2)borato]bis(methanol-upkappaO)iron(II)
S. Ossinger, C. Näther and F. Tuczek, IUCrData 2016, 1, .
Abstract:
The structure determination was undertaken as part of a project on the synthesis of new spin-crossover compounds based on octa­hedral FeII bis­(pyrazol­yl)borate complexes. The asymmetric unit of the title compound, [Fe(H2B(pz)2)2(CH3OH)2] [H2B(pz)2 = di­hydro­bis­(pyrazol-1-yl)borate, C6H8BN4], consists of one FeII cation that is located on a centre of inversion, as well as one methanol mol­ecule and one H2B(pz)2 dianion that occupy general positions. In the crystal, the FeII cations are coordinated by two methanol mol­ecules and four N atoms of two H2B(pz)2 anions within a slightly distorted octa­hedron. Bond lengths and angles between the FeII atom and the H2B(pz)2 anion are comparable to those in related FeII complexes.
BibTeX:
@article{Ossinger2016a,
author = {Sascha Ossinger and Christian Näther and Felix Tuczek},
title = {Bis[dihydrobis(pyrazol-1-yl-upkappaN2)borato]bis(methanol-upkappaO)iron(II)},
journal = {IUCrData},
publisher = {International Union of Crystallography (IUCr)},
year = {2016},
volume = {1},
number = {8},
doi = {https://doi.org/10.1107/s2414314616012529}
}
Funktions- und Verbundmaterialien verstehen und gestalten: Beispiele fächerverbindender Zusammenarbeit
I. Parchmann, S. Schwarzer, A. Staubitz and R. Adelung, Naturwissenschaften im Unterricht - Chemie 2016, 27, 18-22.
BibTeX:
@article{febd1980ce334cd08fe73b06b0e20ab4,
author = {Ilka Parchmann and Stefan Schwarzer and Anne Staubitz and Rainer Adelung},
title = {Funktions- und Verbundmaterialien verstehen und gestalten: Beispiele fächerverbindender Zusammenarbeit},
journal = {Naturwissenschaften im Unterricht - Chemie},
publisher = {Friedrich Verl.},
year = {2016},
volume = {27},
number = {152},
pages = {18-22}
}
Probing the excited state relaxation dynamics of pyrimidine nucleosides in chloroform solution
K. Röttger, H.J.B. Marroux, H. Böhnke, D.T.J. Morris, A.T. Voice, F. Temps, G.M. Roberts and A.J. Orr-Ewing, Faraday Discuss. 2016, .
Abstract:
Ultrafast transient electronic and vibrational absorption spectroscopy (TEAS and TVAS) of 2′-deoxy-cytidine (dC) and 2′-deoxy-thymidine (dT) dissolved in chloroform examines their excited-state dynamics and the recovery of ground electronic state molecules following absorption of ultraviolet light. The chloroform serves as a weakly interacting solvent, allowing comparisons to be drawn with prior experimental studies of the photodynamics of these nucleosides in the gas phase and in polar solvents such as water. The pyrimidine base nucleosides have some propensity to dimerize in aprotic solvents, but the monomer photochemistry can be resolved clearly and is the focus of this study. UV absorption at a wavelength of 260 nm excites a 1ππ* ← S0 transition, but prompt crossing of a significant fraction (50% in dC, 17% in dT) of the 1ππ* population into a nearby 1nπ* state is too fast for the experiments to resolve. The remaining flux on the 1ππ* state leaves the vertical Franck–Condon region and encounters a conical intersection with the ground electronic state of ethylenic twist character. In dC, the 1ππ* state decays to the ground state with a time constant of 1.1 ± 0.1 ps. The lifetime of the 1nπ* state is much longer in the canonical forms of both molecules: recovery of the ground state population from these states occurs with time constants of 18.6 ± 1.1 ps in amino-oxo dC and ∼114 ps in dT, indicating potential energy barriers to the 1nπ*/S0 conical intersections. The small fraction of the imino-oxo tautomer of dC present in solution has a longer-lived 1nπ* state with a lifetime for ground state recovery of 193 ± 55 ps. No evidence is found for photo-induced tautomerization of amino-oxo dC to the imino-oxo form, or for population of low lying triplet states of this nucleoside. In contrast, ∼8% of the UV-excited dT molecules access the long-lived T1 (3ππ*) state through the 1nπ* state. The primary influence of the solvent appears to be the degree to which it destabilizes the states of 1nπ* character, with consequences for the lifetimes of these states as well as the triplet state yields.
BibTeX:
@article{Roettger2016,
author = {Katharina Röttger and Hugo J. B. Marroux and Hendrik Böhnke and David T. J. Morris and Angus T. Voice and Friedrich Temps and Gareth M. Roberts and Andrew J. Orr-Ewing},
title = {Probing the excited state relaxation dynamics of pyrimidine nucleosides in chloroform solution},
journal = {Faraday Discuss.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2016},
doi = {https://doi.org/10.1039/c6fd00068a}
}
Switching of an Azobenzene-Tripod Molecule on Ag(111)
K. Scheil, T.G. Gopakumar, J. Bahrenburg, F. Temps, R.J. Maurer, K. Reuter and R. Berndt, J. Phys. Chem. Lett. 2016, 7, 2080–2084.
Abstract:
The trans–cis isomerization makes azobenzene (AB) a robust molecular switch. Once adsorbed to a metal, however, the switching is inefficient or absent due to rapid excited-state quenching or loss of the trans–cis bistability. We find that tris-[4-(phenylazo)-phenyl]-amine is a rather efficient switch on Ag(111). Using scanning tunneling and atomic force microscopy at sub-molecular resolution along with density functional theory calculations we show that the switching process is no trans–cis isomerisation but rather a reorientation of the N–N bond of an AB unit. It proceeds through a twisting motion of the azo-bridge that leads to a lateral shift of a phenyl ring. Thus the role of the Ag substrate is ambivalent. While it suppresses the original bistability of the azobenzene units it creates a new one by inducing a barrier for the rotation of the N–N bond.
BibTeX:
@article{Scheil2016,
author = {Scheil, Katharina and Gopakumar, Thiruvancheril G. and Bahrenburg, Julia and Temps, Friedrich and Maurer, Reinhard J. and Reuter, Karsten and Berndt, Richard},
title = {Switching of an Azobenzene-Tripod Molecule on Ag(111)},
journal = {J. Phys. Chem. Lett.},
year = {2016},
volume = {7},
pages = {2080–2084},
doi = {https://doi.org/10.1021/acs.jpclett.6b01011}
}
Distance-and spin-resolved spectroscopy of iridium atoms on an iron bilayer
J. Schöneberg, N.M. Caffrey, P. Ferriani, S. Heinze and R. Berndt, Physical Review B 2016, 94, 115418.
Abstract:
The induced spin polarization of Ir atoms on a ferromagnetic Fe double layer on W(110) has been investigated with spin-polarized scanning tunneling microscopy. An unoccupied state is observed with a spin polarization exceeding 60% that is inverted with respect to the Fe layer. This inversion is due to the tunneling gap acting as an orbital and spin filter. Distance dependent measurements show that the spin polarization remains approximately constant over the entire experimentally accessible range, from far in the tunneling regime to 1 Å from the point of contact formation. This is corroborated by density functional theory calculations which show that the inversion of spin polarization occurs within 0.5 Å of the adatom.
BibTeX:
@article{Schoeneberg2016,
author = {Schöneberg, Johannes and Caffrey, Nuala Mai and Ferriani, Paolo and Heinze, Stefan and Berndt, Richard},
title = {Distance-and spin-resolved spectroscopy of iridium atoms on an iron bilayer},
journal = {Physical Review B},
publisher = {APS},
year = {2016},
volume = {94},
number = {11},
pages = {115418},
doi = {https://doi.org/10.1103/PhysRevB.94.115418}
}
Ballistic anisotropic magnetoresistance of single-atom contacts
J. Schöneberg, F. Otte, N. Néel, A. Weismann, Y. Mokrousov, J. Kröger, R. Berndt and S. Heinze, Nano letters 2016, 16, 1450-1454.
Abstract:
Anisotropic magnetoresistance, that is, the sensitivity of the electrical resistance of magnetic materials on the magnetization direction, is expected to be strongly enhanced in ballistic transport through nanoscale junctions. However, unambiguous experimental evidence of this effect is difficult to achieve. We utilize single-atom junctions to measure this ballistic anisotropic magnetoresistance (AMR). Single Co and Ir atoms are deposited on domains and domain walls of ferromagnetic Fe layers on W(110) to control their magnetization directions. They are contacted with nonmagnetic tips in a low-temperature scanning tunneling microscope to measure the junction conductances. Large changes of the magnetoresistance occur from the tunneling to the ballistic regime due to the competition of localized and delocalized d-orbitals, which are differently affected by spin–orbit coupling. This work shows that engineering the AMR at the single atom level is feasible.
BibTeX:
@article{Schöneberg2016,
author = {Schöneberg, J and Otte, Fabian and Néel, Nicolas and Weismann, Alexander and Mokrousov, Yuriy and Kröger, J and Berndt, Richard and Heinze, Stefan},
title = {Ballistic anisotropic magnetoresistance of single-atom contacts},
journal = {Nano letters},
publisher = {ACS Publications},
year = {2016},
volume = {16},
number = {2},
pages = {1450--1454},
doi = {https://doi.org/10.1021/acs.nanolett.5b05071}
}
Design and Synthesis of Photodissociable Ligands Based on Azoimidazoles for Light-Driven Coordination-Induced Spin State Switching in Homogeneous Solution
C. Schütt, G. Heitmann, T. Wendler, B. Krahwinkel and R. Herges, The Journal of Organic Chemistry 2016, 81, 1206-1215.
Abstract:
Light-switchable azoimidazoles were rationally designed and synthesized, and their performance was investigated as photodissociable ligands (PDL) and for spin state switching of Ni porphyrins. The rationally designed ligands exhibit a high photochemical conversion rate (trans -> cis > 98%) and no measurable fatigue over a large number of switching cycles at room temperature under air. As compared to the known phenylazopyridines, the phenylazoimidazoles exhibit a much stronger affinity as axial ligands to Ni porphyrin in the binding trans configuration and a low affinity in their cis form. This affinity switching was used to control the coordination number of Ni2+. Concomitant with the change in coordination number is the change of the spin state from triplet (high spin) to singlet state (low spin). We report on phenylazoimidazole-based PDLs that switch the paramagnetic ratio of the investigated nickel species by up to 70%. Consequently, azoimidazoles exhibit considerably higher switching efficiencies than previously described pyridine-based PDLs.
BibTeX:
@article{Schuett2016,
author = {Christian Schütt and Gernot Heitmann and Thore Wendler and Bahne Krahwinkel and Rainer Herges},
title = {Design and Synthesis of Photodissociable Ligands Based on Azoimidazoles for Light-Driven Coordination-Induced Spin State Switching in Homogeneous Solution},
journal = {The Journal of Organic Chemistry},
publisher = {American Chemical Society (ACS)},
year = {2016},
volume = {81},
number = {3},
pages = {1206-1215},
doi = {https://doi.org/10.1021/acs.joc.5b02817}
}
Spiropyran Based Smart Composites: Memorizing Polymer with Enhanced Molecular Switches
S. Shree, M. Schulz-Senft, X. Jin, Y. Mishra, A. Staubitz and R. Adelung, IFMBE Proceedings (Springer) 2016, 55, 146-148.
Abstract:
We demonstrate the fabrication and response of a smart material combined with spiropyran molecules. Spiropyrans belong to a class of compound that constitute molecular switch. They change color in response to different stimuli such as heat, UV light or mechanical stress. These molecules have been incorporated in polythiourethane (PTU) which is a shape memory polymer. The observations revealed that the molecular switches do not alter the physical properties of the PTU in general; however, both, the spiropyran molecules and smart polymer show changes individually when exposed to heat. The microscopic mechanisms of switching process in response to external stimuli have been discussed in detail.
BibTeX:
@article{Shree2016,
author = {Shree, S. and Schulz-Senft, M. and Jin, X. and Mishra, Y. and Staubitz, A. and Adelung, R.},
title = {Spiropyran Based Smart Composites: Memorizing Polymer with Enhanced Molecular Switches},
journal = {IFMBE Proceedings (Springer)},
year = {2016},
volume = {55},
pages = {146-148},
doi = {https://doi.org/10.1007/978-981-287-736-9_35}
}
Isolated supramolecules on surfaces studied with scanning tunneling microscopy
C. Xie, Q.-M. Wu, R.-N. Li, G.-C. Gu, X. Zhang, N. Li, R. Berndt, J. Kröger, Z.-Y. Shen, S.-M. Hou and Y.-F. Wang, Chinese Chemical Letters 2016, 27, 807–812.
Abstract:
To date, supramolecular chemistry is an ever growing research field owing to its crucial role in molecular catalysis, recognition, medicine, data storage and processing as well as artificial photosynthetic devices. Different isolated supramolecules were prepared by molecular self-assembly on surfaces. This review mainly focuses on supramolecular aggregations on noble metal surfaces studied by scanning tunneling microscopy, including dimers, trimers, tetramers, pentamers, wire-like assemblies and Sierpiński triangular fractals. The variety of self-assembled structures reflects the subtle balance between intermolecular and molecule–substrate interactions, which to some extent may be controlled by molecules, substrates and the molecular coverage. The comparative study of different architectures helps identifying the operative mechanisms that lead to the structural motifs. The application of these mechanisms may lead to novel assemblies with tailored physicochemical properties.
BibTeX:
@article{Xie2016,
author = {Chao Xie and Qi-Meng Wu and Ruo-Ning Li and Gao-Chen Gu and Xue Zhang and Na Li and Richard Berndt and Jörg Kröger and Zi-Yong Shen and Shi-Min Hou and Yong-Feng Wang},
title = {Isolated supramolecules on surfaces studied with scanning tunneling microscopy},
journal = {Chinese Chemical Letters},
publisher = {Elsevier BV},
year = {2016},
volume = {27},
pages = {807–812},
doi = {https://doi.org/10.1016/j.cclet.2016.03.022}
}
Reaction of Phthalocyanines with Graphene on Ir(111)
S.J. Altenburg, M. Lattelais, B. Wang, M.-L. Bocquet and R. Berndt, Journal of the American Chemical Society 2015, 137, 9452–9458.
Abstract:
Iron phthalocyanine (FePc) is adsorbed to graphene on Ir(111) at cryogenic temperature. In addition to mobile FePc with four lobes, imaging and spectroscopy with a scanning tunneling microscope reveal immobile molecules that exhibit fewer lobes. A reversible transformation between four- and three-lobed molecules has been induced by current injection. The data are consistent with chemical bonding of lobes to graphene on Ir, pinning down the graphene area toward Ir. Similar observations are made from NiPc, CoPc, CuPc, and H2Pc. The experimental findings can be explained by ab initio calculations, which suggest that a Diels–Alder-type reaction may be involved with an allyl unit of graphene in the top-fcc moiré registry.
BibTeX:
@article{Altenburg2015,
author = {Altenburg, Simon J. and Lattelais, Marie and Wang, Bin and Bocquet, Marie-Laure and Berndt, Richard},
title = {Reaction of Phthalocyanines with Graphene on Ir(111)},
journal = {Journal of the American Chemical Society},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {137},
number = {29},
pages = {9452–9458},
doi = {https://doi.org/10.1021/jacs.5b05558}
}
Complex magnetic exchange coupling between Co nanostructures and Ni (111) across epitaxial graphene
A. Barla, V. Bellini, S. Rusponi, P. Ferriani, M. Pivetta, F. Donati, F. Patthey, L. Persichetti, S.K. Mahatha, M. Papagno, C. Piamonteze, S. Fichtner, S. Heinze, P. Gambardella, H. Brune and C. Carbone, ACS nano 2015, 10, 1101-1107.
Abstract:
We report on the magnetic coupling between isolated Co atoms as well as small Co islands and Ni(111) mediated by an epitaxial graphene layer. X-ray magnetic circular dichroism and scanning tunneling microscopy combined with density functional theory calculations reveal that Co atoms occupy two distinct adsorption sites, with different magnetic coupling to the underlying Ni(111) surface. We further report a transition from an antiferromagnetic to a ferromagnetic coupling with increasing Co cluster size. Our results highlight the extreme sensitivity of the exchange interaction mediated by graphene to the adsorption site and to the in-plane coordination of the magnetic atoms.
BibTeX:
@article{Barla2015,
author = {Barla, Alessandro and Bellini, Valerio and Rusponi, Stefano and Ferriani, Paolo and Pivetta, Marina and Donati, Fabio and Patthey, François and Persichetti, Luca and Mahatha, Sanjoy K and Papagno, Marco and Piamonteze, Cinthia and Fichtner, Simon and Heinze, Stefan and Gambardella, Pietro and Brune, Harald and Carbone, Carlo},
title = {Complex magnetic exchange coupling between Co nanostructures and Ni (111) across epitaxial graphene},
journal = {ACS nano},
publisher = {ACS Publications},
year = {2015},
volume = {10},
number = {1},
pages = {1101--1107},
doi = {https://doi.org/10.1021/acsnano.5b06410}
}
Light-Controlled Conductance Switching in Azobenzene-Containing MWCNT–Polymer Nanocomposites
S.W. Basuki, V. Schneider, T. Strunskus, M. Elbahri and F. Faupel, ACS Appl. Mater. Interfaces 2015, 7, 11257-11262.
Abstract:
We report on reversible light-controlled conductance switching in devices consisting of multiwalled carbon nanotube (MWCNT)–polymer nanocomposites blended with azobenzene molecules and photoisomerization of the latter. Both the azobenzene molecules and MWCNT, which are functionalized with carboxyl groups (MWCNT-COOH), are embedded independently in a poly(methyl methacrylate) matrix, and thin films are prepared by using a simple spin-coating technique. We demonstrate the feasibility of the present concept with a photocurrent switching amplitude of almost 10%.
BibTeX:
@article{Basuki2015,
author = {Sri Wahyuni Basuki and Viktor Schneider and Thomas Strunskus and Mady Elbahri and Franz Faupel},
title = {Light-Controlled Conductance Switching in Azobenzene-Containing MWCNT–Polymer Nanocomposites},
journal = {ACS Appl. Mater. Interfaces},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {7},
number = {21},
pages = {11257--11262},
doi = {https://doi.org/10.1021/acsami.5b01319}
}
Highly Efficient Thermal and Light-Induced Spin-State Switching of an Fe(II) Complex in Direct Contact with a Solid Surface
M. Bernien, H. Naggert, L.M. Arruda, L. Kipgen, F. Nickel, J. Miguel, C.F. Hermanns, A. Krüger, D. Krüger, E. Schierle, E. Weschke, F. Tuczek and W. Kuch, ACS Nano 2015, 9, 8960-8966.
Abstract:
Spin crossover (SCO) complexes possess a bistable spin state that reacts sensitively to changes in temperature or excitation with light. These effects have been well investigated in solids and solutions, while technological applications require the immobilization and contacting of the molecules at surfaces, which often results in the suppression of the SCO. We report on the thermal and light-induced SCO of [Fe(bpz)2phen] molecules in direct contact with a highly oriented pyrolytic graphite surface. We are able to switch on the magnetic moment of the molecules by illumination with green light at T = 6 K, and off by increasing the temperature to 65 K. The light-induced switching process is highly efficient leading to a complete spin conversion from the low-spin to the high-spin state within a submonolayer of molecules. [Fe(bpz)2phen] complexes immobilized on weakly interacting graphite substrates are thus promising candidates to realize the vision of an optically controlled molecular logic unit for spintronic devices.
BibTeX:
@article{Bernien2015,
author = {Matthias Bernien and Holger Naggert and Lucas M. Arruda and Lalminthang Kipgen and Fabian Nickel and Jorge Miguel and Christian F. Hermanns and Alex Krüger and Dennis Krüger and Enrico Schierle and Eugen Weschke and Felix Tuczek and Wolfgang Kuch},
title = {Highly Efficient Thermal and Light-Induced Spin-State Switching of an Fe(II) Complex in Direct Contact with a Solid Surface},
journal = {ACS Nano},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {9},
number = {9},
pages = {8960--8966},
doi = {https://doi.org/10.1021/acsnano.5b02840}
}
Shot noise from single atom contacts in a scanning tunneling microscope
A. Burtzlaff, N.L. Schneider, A. Weismann and R. Berndt, Surface Science 2015, 643, 10-12.
Abstract:
The shot noise of the current through single-atom contacts has been measured in a scanning tunneling microscope at a temperature of 5 K. Electrical measurements at frequencies up to 120 kHz were performed on Au, Fe, and Co atoms on Au(111) using Au tips. The data from Fe and Co indicate spin polarized transmission through a single conductance channel. Optical measurements at sub-petahertz frequencies were carried out on Cu adatoms on Cu(111) using Cu tips. The data are consistent with previous observations from coinage metal contacts.
BibTeX:
@article{Burtzlaff2015,
author = {Burtzlaff, Andreas and Schneider, Natalia L. and Weismann, Alexander and Berndt, Richard},
title = {Shot noise from single atom contacts in a scanning tunneling microscope},
journal = {Surface Science},
publisher = {Elsevier BV},
year = {2015},
volume = {643},
pages = {10-12},
doi = {https://doi.org/10.1016/j.susc.2015.07.006}
}
Competing Forces during Contact Formation between a Tip and a Single Molecule
N.M. Caffrey, K. Buchmann, N. Hauptmann, C. Lazo, P. Ferriani, S. Heinze and R. Berndt, Nano Lett. 2015, 15, 5156–5160.
Abstract:
Sn-phthalocyanine adsorbs on Ag(111) in a physisorbed or a chemisorbed configuration. Both structures are contacted with the tip of a combined scanning tunneling and atomic force microscope. The tunneling conductances of both configurations exhibit similar exponential variations with the tip–molecule distance. The short-range forces, however, display nontrivial distance dependencies. First-principles calculations reproduce the experimental results. Both attractive and repulsive interactions occur between the tip and different parts of the molecule due to a combination of bond formation and electrostatic interactions with the tip electric dipole. Consequently, deformations occur and the force varies in the resulting unexpected fashion.
BibTeX:
@article{Caffrey2015,
author = {Caffrey, Nuala M. and Buchmann, Kristof and Hauptmann, Nadine and Lazo, Cesar and Ferriani, Paolo and Heinze, Stefan and Berndt, Richard},
title = {Competing Forces during Contact Formation between a Tip and a Single Molecule},
journal = {Nano Lett.},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {15},
number = {8},
pages = {5156–5160},
doi = {https://doi.org/10.1021/acs.nanolett.5b01383}
}
Efficient global optimization of reactive force-field parameters
M. Dittner, J. Müller, H.M. Aktulga and B. Hartke, J. Comput. Chem. 2015, 36, 1550-1561.
Abstract:
Reactive force fields make low-cost simulations of chemical reactions possible. However, optimizing them for a given chemical system is difficult and time-consuming. We present a high-performance implementation of global force-field parameter optimization, which delivers parameter sets of the same quality with much less effort and in far less time than before, and also offers excellent parallel scaling. We demonstrate these features with example applications targeting the ReaxFF force field.
BibTeX:
@article{Dittner2015,
author = {Mark Dittner and Julian Müller and Hasan Metin Aktulga and Bernd Hartke},
title = {Efficient global optimization of reactive force-field parameters},
journal = {J. Comput. Chem.},
publisher = {Wiley-Blackwell},
year = {2015},
volume = {36},
number = {20},
pages = {1550--1561},
doi = {https://doi.org/10.1002/jcc.23966}
}
Synthesis of Functionalized Perfluorinated Porphyrins for Improved Spin Switching
M. Dommaschk, C. Näther and R. Herges, The Journal of Organic Chemistry 2015, 80, 8496-8500.
Abstract:
The authors established a method to synthesize perfluorinated meso-​phenylporphyrins with one Ph group bearing a substituent in the ortho position. These novel electron-​deficient porphyrins are interesting for model enzymes, catalysis, photodynamic therapy, and electron transfer. The key step is the synthesis of an I-​substituted porphyrin and its Suzuki cross coupling with boronic acid derivs. The authors applied the novel strategy to synthesize a highly electron-​deficient, azopyridine-​substituted Ni-​porphyrin that undergoes an improved ligand-​driven coordination-​induced spin-​state switch.
BibTeX:
@article{Dommaschk2015b,
author = {M. Dommaschk and C. Näther and R. Herges},
title = {Synthesis of Functionalized Perfluorinated Porphyrins for Improved Spin Switching},
journal = {The Journal of Organic Chemistry},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {80},
number = {17},
pages = {8496-8500},
doi = {https://doi.org/10.1021/acs.joc.5b01524}
}
Photoswitchable Magnetic Resonance Imaging Contrast by Improved Light-Driven Coordination-Induced Spin State Switch
M. Dommaschk, M. Peters, F. Gutzeit, C. Schütt, C. Näther, F.D. Sönnichsen, S. Tiwari, C. Riedel, S. Boretius and R. Herges, Journal of the American Chemical Society 2015, 137, 7552–7555.
Abstract:
We present a fully reversible and highly efficient on–off photoswitching of magnetic resonance imaging (MRI) contrast with green (500 nm) and violet-blue (435 nm) light. The contrast change is based on intramolecular light-driven coordination-induced spin state switch (LD-CISSS), performed with azopyridine-substituted Ni-porphyrins. The relaxation time of the solvent protons in 3 mM solutions of the azoporphyrins in DMSO was switched between 3.5 and 1.7 s. The relaxivity of the contrast agent changes by a factor of 6.7. No fatigue or side reaction was observed, even after >100 000 switching cycles in air at room temperature. Electron-donating substituents at the pyridine improve the LD-CISSS in two ways: better photostationary states are achieved, and intramolecular binding is enhanced.
BibTeX:
@article{Dommaschk2015,
author = {Dommaschk, Marcel and Peters, Morten and Gutzeit, Florian and Schütt, Christian and Näther, Christian and Sönnichsen, Frank D. and Tiwari, Sanjay and Riedel, Christian and Boretius, Susann and Herges, Rainer},
title = {Photoswitchable Magnetic Resonance Imaging Contrast by Improved Light-Driven Coordination-Induced Spin State Switch},
journal = {Journal of the American Chemical Society},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {137},
number = {24},
pages = {7552–7555},
doi = {https://doi.org/10.1021/jacs.5b00929}
}
Coordination-Induced Spin-State Switching with Nickel Chlorin and Nickel Isobacteriochlorin
M. Dommaschk, V. Thoms, C. Schütt, C. Näther, R. Puttreddy, K. Rissanen and R. Herges, Inorganic Chemistry 2015, 54, 9390-9392.
Abstract:
The authors present the first coordination-​induced spin-​state switching with nickel chlorin and nickel isobacteriochlorin. The spin-​state switching was monitored by UV-​visible spectroscopy and NMR titrn. expts. The assocn. consts. (K1 and K2) and thermodn. parameters (ΔH and ΔS) of the coordination of pyridine were detd. The first x-​ray analyses of a paramagnetic nickel chlorin and a nickel isobacteriochlorin provide further information about the structure of the octahedral complexes. Nickel chlorin and even more pronounced nickel isobacteriochlorin exhibit stronger coordination of axial ligands compared to the corresponding nickel porphyrin and thus provide the basis for more efficient spin-​switching systems.
BibTeX:
@article{Dommaschk2015a,
author = {Marcel Dommaschk and Vanessa Thoms and Christian Schütt and Christian Näther and Rakesh Puttreddy and Kari Rissanen and Rainer Herges},
title = {Coordination-Induced Spin-State Switching with Nickel Chlorin and Nickel Isobacteriochlorin},
journal = {Inorganic Chemistry},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {54},
number = {19},
pages = {9390-9392},
doi = {https://doi.org/10.1021/acs.inorgchem.5b01756}
}
Photoswitchable molecular dipole antennas with tailored coherent coupling in glassy composite
M. Elbahri, A.U. Zillohu, B. Gothe, M.K. Hedayati, R. Abdelaziz, H.J. El-Khozondar, M. Bawa'aneh, M. Abdelaziz, A. Lavrinenko, S. Zhukovsky and S. Homaeigohar, Light: Science & Applications 2015, 4, e316.
Abstract:
Here, we introduce the first experimental proof of coherent oscillation and coupling of photoswitchable molecules embedded randomly in a polymeric matrix and acting cooperatively upon illumination with UV light. In particular, we demonstrate the specular reflection and Brewster phenomenon alteration of photochromic molecular dipole antennas. We successfully demonstrate the concept of Brewster wavelength, which is based on the dipolar interaction between radiating dipoles and the surrounding matrix possessing a net dipole moment, as a key tool for highly localized sensing of matrix polarity. We also introduce the concept of ‘tailored molecular photonic coupling’ while highlighting the role of interferences for the design of optically active media by adjusting the photonic response of the medium with the real and imaginary refractive index of photoswitchable molecules in the ‘ON’ state. Our results enhance our fundamental understanding of coherent dipole radiation and open a new vein of research based on glassy disordered dipolar composites that act as macroscopic antenna with cooperative action; furthermore, these results have important implications for new design rules of tailored photonics.
BibTeX:
@article{Elbahri2015,
author = {Mady Elbahri and Ahnaf Usman Zillohu and Bastian Gothe and Mehdi Keshavarz Hedayati and Ramzy Abdelaziz and Hala Jarallah El-Khozondar and Muhammad Bawa'aneh and Moheb Abdelaziz and Andrei Lavrinenko and Sergei Zhukovsky and Shahin Homaeigohar},
title = {Photoswitchable molecular dipole antennas with tailored coherent coupling in glassy composite},
journal = {Light: Science & Applications},
publisher = {Nature Publishing Group},
year = {2015},
volume = {4},
number = {7},
pages = {e316},
doi = {https://doi.org/10.1038/lsa.2015.89}
}
Light-Triggered Control of Plasmonic Refraction and Group Delay by Photochromic Molecular Switches
M. Großmann, A. Klick, C. Lemke, J. Falke, M. Black, J. Fiutowski, A.J. Goszczak, E. Sobolewska, A.U. Zillohu, M.K. Hedayati, H.-G. Rubahn, F. Faupel, M. Elbahri and M. Bauer, ACS Photonics 2015, 2, 1327-1332.
Abstract:
An interface supporting plasmonic switching is prepared from a gold substrate coated with a polymer film doped with photochromic molecular switches. A reversible light-induced change in the surface plasmon polariton dispersion curve of the interface is experimentally demonstrated, evidencing reversible switching of the surface plasmon polariton group and phase velocity. The switching capabilities of the interface are furthermore successfully applied to achieve focus control of a plasmonic lens. The results imply the realization of nonvolatile and reversible plasmonic switching units providing complex functionalities based on surface plasmon refraction and group delay.
BibTeX:
@article{Grosmann2015,
author = {Malte Großmann and Alwin Klick and Christoph Lemke and Julian Falke and Maximilian Black and Jacek Fiutowski and Arkadiusz Jaroslaw Goszczak and Elzbieta Sobolewska and Ahnaf Usman Zillohu and Mehdi Keshavarz Hedayati and Horst-Guenter Rubahn and Franz Faupel and Mady Elbahri and Michael Bauer},
title = {Light-Triggered Control of Plasmonic Refraction and Group Delay by Photochromic Molecular Switches},
journal = {ACS Photonics},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {2},
number = {9},
pages = {1327--1332},
doi = {https://doi.org/10.1021/acsphotonics.5b00315}
}
Joining Hydroxyazobenzene and Mannose under Mitsunobu Conditions
J. Hain, V. Chandrasekaran and T.K. Lindhorst, Israel Journal of Chemistry 2015, 55, 383-386.
Abstract:
The Mitsunobu reaction has been revisited to join hydroxyazobenzene and mannose derivatives to supply photoswitchable glycoconjugates. These are suited to modulating and controlling carbohydrate-lectin interactions, as well as to switching bacterial adhesion to surfaces. Employing hydroxyazobenzene in a Mitsunobu protocol, free mannose led to a mixture of azobenzene pyranosides and furanosides. Protected reducing mannose derivatives can give good yields of azobenzene β-D-mannopyranoside, and unprotected alkyl α-D-mannosides can be converted to 6-O-azobenzene-modified glycosides in a single step. Thus, valuable “sweet switches” can be obtained under Mitsunobu conditions, requiring a minimum (or no) protecting group chemistry.
BibTeX:
@article{Hain2015,
author = {Julia Hain and Vijayanand Chandrasekaran and Thisbe K. Lindhorst},
title = {Joining Hydroxyazobenzene and Mannose under Mitsunobu Conditions},
journal = {Israel Journal of Chemistry},
publisher = {Wiley-Blackwell},
year = {2015},
volume = {55},
number = {3-4},
pages = {383--386},
doi = {https://doi.org/10.1002/ijch.201400211}
}
Laterally Mounted Azobenzenes on Platforms
M. Hammerich and R. Herges, The Journal of Organic Chemistry 2015, 11233–11236.
Abstract:
Triazatriangulenium ions have previously been used as platforms to prep. self-​assembled monolayers of functional mols. such as azobenzenes with vertical orientation and that are free-​standing on gold surfaces. We have now prepd. azobenzenes that are spanned between two posts which are attached on two platforms. Absorbed on a gold surface, the azobenzene should be laterally oriented at a distance of more than 4 Å above and thus electronically decoupled from the surface, and the system should perform a muscle-​type movement upon isomerization.
BibTeX:
@article{Hammerich2015,
author = {Melanie Hammerich and Rainer Herges},
title = {Laterally Mounted Azobenzenes on Platforms},
journal = {The Journal of Organic Chemistry},
publisher = {American Chemical Society (ACS)},
year = {2015},
pages = {11233–11236},
doi = {https://doi.org/10.1021/acs.joc.5b02262}
}
Reactive force fields made simple
B. Hartke and S. Grimme, Phys. Chem. Chem. Phys. 2015, 17, 16715-16718.
Abstract:
Generating a reactive force field for a given chemical reaction is turned from a many-months project for experts into a task of a few hours for a non-specialist, by joining the newly developed quantum-mechanically derived force field (QMDFF) and Warshel's time-tested empirical valence bond (EVB) idea. Three first example applications demonstrate that this works not just for simple atom exchange but also for more complicated reactions.
BibTeX:
@article{Hartke2015,
author = {Bernd Hartke and Stefan Grimme},
title = {Reactive force fields made simple},
journal = {Phys. Chem. Chem. Phys.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2015},
volume = {17},
number = {26},
pages = {16715--16718},
doi = {https://doi.org/10.1039/c5cp02580j}
}
Interactions between two C60 molecules measured by scanning probe microscopies
N. Hauptmann, C. González, F. Mohn, L. Gross, G. Meyer and R. Berndt, Nanotechnology 2015, 445703.
Abstract:
C60 -functionalized tips are used to probe C60 molecules on Cu(111) with scanning tunneling and atomic force microscopy. Distinct and complex intramolecular contrasts are found. Maximal attractive forces are observed when for both molecules a [6,6] bond faces a hexagon of the other molecule. Density functional theory calculations including parameterized van der Waals interactions corroborate the observations.
BibTeX:
@article{Hauptmann2015a,
author = {Hauptmann, Nadine and González, César and Mohn, Fabian and Gross, Leo and Meyer, Gerhard and Berndt, Richard},
title = {Interactions between two C60 molecules measured by scanning probe microscopies},
journal = {Nanotechnology},
year = {2015},
pages = {445703},
doi = {https://doi.org/10.1088/0957-4484/26/44/445703}
}
High-conductance surface-anchoring of a mechanically flexible platform-based porphyrin complex
N. Hauptmann, L. Groß, K. Buchmann, K. Scheil, C. Schütt, F. Otte, R. Herges, C. Herrmann and R. Berndt, New J. Phys. 2015, 17, 013012.
Abstract:
The conductances of molecular model junctions comprising a triazatriangulenium platform with or without an ethynyl spacer and an upright Zn-porphyrin are probed with a low-temperature scanning probe microscope. The platform alone is found to be highly conductive. The ethynyl-linked Zn-porphyrin moiety reduces the conductance by three orders of magnitude and leads to an unexpected, non-monotonous variation of the force that was measured simultaneously at the tip of the microscope. Density functional theory calculations show that this variation results from an induced tilting of the porphyrin.
BibTeX:
@article{Hauptmann2015,
author = {Hauptmann, Nadine and Groß, Lynn and Buchmann, Kristof and Scheil, Katharina and Schütt, Christian and Otte, Franziska and Herges, Rainer and Herrmann, Carmen and Berndt, Richard},
title = {High-conductance surface-anchoring of a mechanically flexible platform-based porphyrin complex},
journal = {New J. Phys.},
year = {2015},
volume = {17},
pages = {013012},
doi = {https://doi.org/10.1088/1367-2630/17/1/013012}
}
Rapid Reversible Photoswitching of Integrin-Mediated Adhesion at the Single-Cell Level
L.F. Kadem, M. Holz, K.G. Suana, Q. Li, C. Lamprecht, R. Herges and C. Selhuber-Unkel, Adv. Mater. 2015, 28, 1799-1802.
Abstract:
Rapid and reversible photoswitching of cell adhesion is achieved by c(RGDfK)-azobenzenes embedded in a poly(ethylene glycol) background on surfaces. The light-induced cis–trans-isomerization of the azobenzene enables switching of cell adhesion on the surface. Reversibility of switching over several consecutive switching cycles is demonstrated by single-cell force spectroscopy.
BibTeX:
@article{Kadem2015,
author = {Laith F. Kadem and Michelle Holz and Kristine Grace Suana and Qian Li and Constanze Lamprecht and Rainer Herges and Christine Selhuber-Unkel},
title = {Rapid Reversible Photoswitching of Integrin-Mediated Adhesion at the Single-Cell Level},
journal = {Adv. Mater.},
publisher = {Wiley-Blackwell},
year = {2015},
volume = {28},
number = {9},
pages = {1799--1802},
url = {http://dx.doi.org/10.1002/adma.201504394},
doi = {https://doi.org/10.1002/adma.201504394}
}
Surface Trapping and STM Observation of Conformational Isomers of a Bis(Terpyridine) Ligand from Metallosupramolecular Grids
S. Karan, C. Hamann, H. Tang, A.R. Stefankiewicz, J.-M. Lehn and R. Berndt, ChemPhysChem 2015, 16, 1370–1373.
Abstract:
Tetranuclear Co-grid complexes incorporating bis-tridentate ligands, namely 4,6-bis(2,2’-bipyrid-6-yl)-2-phenylpyrimidine, were electrosprayed onto a Au(111) substrate under an ultra-high vacuum. Fragmentation occurs leaving the ligands in four different conformations. Most ligands are found to form H-bonded dimers. The most abundant conformer of the ligand on the Au surface is an asymmetric form, which has not been observed before. The present results indicate that the fragmentation of coordination compounds during the deposition process, in principle, allows for surface trapping, identification, and investigation of high energy, out-of-equilibrium conformations of the ligand molecules at low temperatures, which otherwise would not be observable.
BibTeX:
@article{Karan2015,
author = {Karan, Sujoy and Hamann, Christian and Tang, Hao and Stefankiewicz, Artur R. and Lehn, Jean-Marie and Berndt, Richard},
title = {Surface Trapping and STM Observation of Conformational Isomers of a Bis(Terpyridine) Ligand from Metallosupramolecular Grids},
journal = {ChemPhysChem},
year = {2015},
volume = {16},
pages = {1370–1373},
doi = {https://doi.org/10.1002/cphc.201500100}
}
Shifting the Voltage Drop in Electron Transport Through a Single Molecule
S. Karan, D. Jacob, M. Karolak, C. Hamann, Y. Wang, A. Weismann, A.I. Lichtenstein and R. Berndt, Phys. Rev. Lett. 2015, 115, 016802.
Abstract:
A Mn-porphyrin was contacted on Au(111) in a low-temperature scanning tunneling microscope (STM). Differential conductance spectra show a zero-bias resonance that is due to an underscreened Kondo effect according to many-body calculations. When the Mn center is contacted by the STM tip, the spectrum appears to invert along the voltage axis. A drastic change in the electrostatic potential of the molecule involving a small geometric relaxation is found to cause this observation.
BibTeX:
@article{Karan2015a,
author = {Karan, Sujoy and Jacob, David and Karolak, Michael and Hamann, Christian and Wang, Yongfeng and Weismann, Alexander and Lichtenstein, Alexander I. and Berndt, Richard},
title = {Shifting the Voltage Drop in Electron Transport Through a Single Molecule},
journal = {Phys. Rev. Lett.},
year = {2015},
volume = {115},
pages = {016802},
doi = {https://doi.org/10.1103/PhysRevLett.115.016802}
}
Spin Manipulation by Creating Single-Molecule Radical Cations
S. Karan, N. Li, Y. Zhang, Y. He, I.-P. Hong, H. Song, J.-T. Lü, Y. Wang, L. Peng, K. Wu, G.S. Michelitsch, R.J. Maurer, K. Diller, K. Reuter, A. Weismann and R. Berndt, Phys. Rev. Lett 2015, 115, 027201.
Abstract:
All-trans-retinoic acid (ReA), a closed-shell organic molecule comprising only C, H, and O atoms, is investigated on a Au(111) substrate using scanning tunneling microscopy and spectroscopy. In dense arrays single ReA molecules are switched to a number of states, three of which carry a localized spin as evidenced by conductance spectroscopy in high magnetic fields. The spin of a single molecule may be reversibly switched on and off without affecting its neighbors. We suggest that ReA on Au is readily converted to a radical by the abstraction of an electron.
BibTeX:
@article{Karan2015b,
author = {Karan, Sujoy and Li, Na and Zhang, Yajie and He, Yang and Hong, I-Po and Song, Huanjun and Lü, Jing-Tao and Wang, Yongfeng and Peng, Lianmao and Wu, Kai and Michelitsch, Georg S. and Maurer, Reinhard J. and Diller, Katharina and Reuter, Karsten and Weismann, Alexander and Berndt, Richard},
title = {Spin Manipulation by Creating Single-Molecule Radical Cations},
journal = {Phys. Rev. Lett},
year = {2015},
volume = {115},
pages = {027201},
doi = {https://doi.org/10.1103/PhysRevLett.116.027201}
}
Optically switchable natural silk
I. Krasnov, N.R. Krekiehn, C. Krywka, U. Jung, A.U. Zillohu, T. Strunskus, M. Elbahri, O.M. Magnussen and M. Müller, Appl. Phys. Lett. 2015, 106, 093702.
Abstract:
An optically active bio-material is created by blending natural silk fibers with photoisomerizable chromophore molecules—azobenzenebromide (AzBr). The material converts the energy of unpolarized light directly into mechanical work with a well-defined direction of action. The feasibility of the idea to produce optically driven microsized actuators on the basis of bio-material (silk) is proven. The switching behavior of the embedded AzBr molecules was studied in terms of UV/Vis spectroscopy. To test the opto-mechanical properties of the modified fibers and the structural changes they undergo upon optically induced switching, single fiber X-ray diffraction with a micron-sized synchrotron radiation beam was combined in situ with optical switching as well as with mechanical testing and monitoring. The crystalline regions of silk are not modified by the presence of the guest molecules, hence occupy only the amorphous part of the fibers. It is shown that chromophore molecules embedded into fibers can be reversibly switched between the trans and cis conformation by illumination with light of defined wavelengths. The host fibers respond to this switching with a variation of the internal stress. The amplitude of the mechanical response is independent of the applied external stress and its characteristic time is shorter than the relaxation time of the usual mechanical response of silk.
BibTeX:
@article{Krasnov2015,
author = {Krasnov, Igor and Krekiehn, Nicolai R. and Krywka, Christina and Jung, Ulrich and Zillohu, Ahnaf U. and Strunskus, Thomas and Elbahri, Mady and Magnussen, Olaf M. and Müller, Martin},
title = {Optically switchable natural silk},
journal = {Appl. Phys. Lett.},
publisher = {AIP Publishing},
year = {2015},
volume = {106},
pages = {093702},
doi = {https://doi.org/10.1063/1.4913912}
}
Fractional dynamics in silk – from molecular picosecond sub-diffusion to macroscopic long-time relaxation
I. Krasnov, T. Seydel and M. Muller, Physical Review E 2015, 91, 042716.
Abstract:
Structural relaxations in humid silk fibers exposed to tensile stress have been reported to take place on a very wide range of time scales from a few milliseconds to several hours. The time-dependence of the measured tensile force following a quasi-instantaneously applied external strain on the fibers can be understood in terms of a fractional viscoelastic relaxation function introducing memory effects by which the mechanical state of a fiber depends on its tensile history. An analog fractional relaxation also gives rise to the subdiffusion observed on picosecond time scales which governs the mobility of the amorphous polymer chains and adsorbed water on the molecular level. The reduction of the subdiffusive memory effect in stretched fibers compared to native fibers is consistent with the higher order of the polymers in the stretched state.
BibTeX:
@article{Krasnov2015a,
author = {Krasnov, Igor and Seydel, Tilo and Muller, Martin},
title = {Fractional dynamics in silk – from molecular picosecond sub-diffusion to macroscopic long-time relaxation},
journal = {Physical Review E},
year = {2015},
volume = {91},
pages = {042716},
doi = {https://doi.org/10.1103/PhysRevE.91.042716}
}
UV/Vis Spectroscopy Studies of the Photoisomerization Kinetics in Self-Assembled Azobenzene-Containing Adlayers
N.R. Krekiehn, M. Müller, U. Jung, S. Ulrich, R. Herges and O.M. Magnussen, Langmuir 2015, 31, 8362–8370.
Abstract:
Direct comparative studies of the photoisomerization of azobenzene derivatives in self-assembled adlayers on Au and as free molecules in dichloromethane solution were performed using UV/vis spectroscopy. For all studied systems a highly reversible trans–cis isomerization in the adlayer is observed. Quantitative studies of the absorbance changes and photoisomerization kinetics reveal that in azobenzenes mounted as freestanding vertical groups on the surface via triazatriangulene-based molecular platforms photoswitching is nearly uninhibited by the local environment in the adlayer. The blue-shift of the π–π* transition in adlayers of these molecules is in good agreement with theoretical studies of the effect of excitonic coupling between the molecules. In contrast, in azobenzene-containing thiol self-assembled monolayers the fraction of photoswitching molecules and the photoisomerization kinetics are significantly reduced compared to free molecules in solution.
BibTeX:
@article{Krekiehn2015,
author = {Krekiehn, N. R. and Müller, M. and Jung, U. and Ulrich, S. and Herges, R. and Magnussen, O. M.},
title = {UV/Vis Spectroscopy Studies of the Photoisomerization Kinetics in Self-Assembled Azobenzene-Containing Adlayers},
journal = {Langmuir},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {31},
number = {30},
pages = {8362–8370},
doi = {https://doi.org/10.1021/acs.langmuir.5b01645}
}
Switching first contact: photocontrol of E. coli adhesion to human cells
L. Mockl, A. Muller, C. Brauchle and T.K. Lindhorst, Chem. Commun. 2015, 1254-1257.
Abstract:
We have shown previously that carbohydrate-specific bacterial adhesion to a non-physiological surface can be photocontrolled by reversible E/Z isomerisation using azobenzene-functionalised sugars. Here, this approach is applied to the surface of human cells. We show not only that bacterial adhesion to the azobenzene glycoside-modified cell surface is higher in the E than in the Z state, but add data about the specific modulation of the effect.
BibTeX:
@article{Mockl2015,
author = {Mockl, Leonhard and Muller, Anne and Brauchle, C and Lindhorst, Thisbe K},
title = {Switching first contact: photocontrol of E. coli adhesion to human cells},
journal = {Chem. Commun.},
publisher = {The Royal Society of Chemistry},
year = {2015},
pages = {1254-1257},
doi = {https://doi.org/10.1039/C5CC08884D}
}
Synthesis of Bifunctional Azobenzene Glycoconjugates for Cysteine-Based Photosensitive Cross-Linking with Bioactive Peptides
A. Müller, H. Kobarg, V. Chandrasekaran, J. Gronow, F.D. Sönnichsen and T.K. Lindhorst, Chemistry - A European Journal 2015, 21, 13723-13731.
Abstract:
Azobenzene linker molecules can be utilized to control peptide/protein function when they are ligated to appropriately spaced amino acid side chains of the peptide. This is because the photochemical E/Z isomerization of the azobenzene N[DOUBLE BOND]N double bond allows to switch peptide conformation between folded and unfolded. In this context, we have introduced carbohydrate-functionalized azobenzene derivatives in order to advance the biocompatible properties of azobenzene peptide linkers. Chloroacetamide-functionalized and O-allylated carbohydrate derivatives were synthesized and conjugated with azobenzene to achieve new bifunctional cross-linkers, in order to allow ligation to cysteine side chains by nucleophilic substitution or thiol-ene reaction, respectively. The photochromic properties of the new linker glycoconjugates were determined and first ligation reactions performed.
BibTeX:
@article{Mueller2015,
author = {Anne Müller and Hauke Kobarg and Vijayanand Chandrasekaran and Joana Gronow and Frank D. Sönnichsen and Thisbe K. Lindhorst},
title = {Synthesis of Bifunctional Azobenzene Glycoconjugates for Cysteine-Based Photosensitive Cross-Linking with Bioactive Peptides},
journal = {Chemistry - A European Journal},
publisher = {Wiley-Blackwell},
year = {2015},
volume = {21},
number = {39},
pages = {13723--13731},
doi = {https://doi.org/10.1002/chem.201501571}
}
Vacuum-evaporable spin-crossover complexes: physicochemical properties in the crystalline bulk and in thin films deposited from the gas phase
H. Naggert, J. Rudnik, L. Kipgen, M. Bernien, F. Nickel, L.M. Arruda, W. Kuch, C. Näther and F. Tuczek, J. Mater. Chem. C 2015, 3, 7870-7877.
Abstract:
Four analogues of the spin-crossover complex [Fe(H2Bpz2)2(phen)] (H2Bpz2 = dihydrobis(pyrazolyl)borate; 2) containing functionalized 1,10-phenanthroline (phen) ligands have been prepared; i.e., [Fe(H2Bpz2)2(L)], L = 4-methyl-1,10-phenanthroline (3), 5-chloro-1,10-phenanthroline (4), 4,7-dichloro-1,10-phenanthroline (5), and 4,7-dimethyl-1,10-phenanthroline (6). The systems are investigated by magnetic susceptibility measurements and a range of spectroscopies in the solid state and in thin films obtained by physical vapour deposition (PVD). Thermal as well as light-induced SCO behaviour is observed for 3–6 in the films. By contrast, thermal SCO in the solid state occurs only for 3 and 4 but is absent for 5 and 6. These findings are discussed in the light of cooperative and intermolecular interactions.
BibTeX:
@article{Naggert2015,
author = {H. Naggert and J. Rudnik and L. Kipgen and M. Bernien and F. Nickel and L. M. Arruda and W. Kuch and C. Näther and F. Tuczek},
title = {Vacuum-evaporable spin-crossover complexes: physicochemical properties in the crystalline bulk and in thin films deposited from the gas phase},
journal = {J. Mater. Chem. C},
publisher = {Royal Society of Chemistry (RSC)},
year = {2015},
volume = {3},
number = {30},
pages = {7870--7877},
doi = {https://doi.org/10.1039/c5tc00930h}
}
Molecular anisotropic magnetoresistance
F. Otte, S. Heinze and Y. Mokrousov, Phys. Rev. B 2015, 92, 220411.
Abstract:
Using density functional theory calculations, we demonstrate that the effect of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude with respect to conventional bulk ferromagnets in junctions containing molecules sandwiched between ferromagnetic leads. We study ballistic transport in metal-benzene complexes contacted by 3d transition-metal wires. We show that a gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symmetry filtering properties of the molecules. We further discuss how this molecular anisotropic magnetoresistance (MAMR) can be tuned by the proper choice of materials and their electronic properties.
BibTeX:
@article{PhysRevB.92.220411,
author = {Otte, Fabian and Heinze, Stefan and Mokrousov, Yuriy},
title = {Molecular anisotropic magnetoresistance},
journal = {Phys. Rev. B},
publisher = {American Physical Society},
year = {2015},
volume = {92},
pages = {220411},
doi = {https://doi.org/10.1103/PhysRevB.92.220411}
}
Indandiazocines: unidirectional molecular switches
T. Raeker and Hartke, ScienceOpen Research 2015, published online.
Abstract:
We report theoretical investigations on azobenzene-based indandiazocines, novel chiral systems that perform unidirectional cis ↔ trans isomerizations upon photoexcitation. For three different systems of this kind, we have simulated excited-state surface-hopping trajectories for both isomerization directions, using a configuration-interaction treatment based on system-specifically reparametrized semiempirical AM1 theory. Our results are also compared to experimental and theoretical results for the parent system diazocine. We show that, as intended by design, the trans → cis bending of the azo unit in these indandiazocines can only happen in one of the two possible directions due to steric constraints, which is a new feature for photoswitches and a necessary prerequisite for directional action at the nanoscale.
BibTeX:
@article{2015,
author = {Raeker, T. and Hartke,},
title = {Indandiazocines: unidirectional molecular switches},
journal = {ScienceOpen Research},
publisher = {ScienceOpen},
year = {2015},
pages = {published online},
doi = {https://doi.org/10.14293/s2199-1006.1.sor-chem.ardtln.v1}
}
Ultraviolet Absorption Induces Hydrogen-Atom Transfer in G⋅C Watson-Crick DNA Base Pairs in Solution
K. Röttger, H.J.B. Marroux, M.P. Grubb, P.M. Coulter, H. Böhnke, A.S. Henderson, M.C. Galan, F. Temps, A.J. Orr-Ewing and G.M. Roberts, Angewandte Chemie International Edition 2015, 54, 14719-14722.
Abstract:
Ultrafast deactivation pathways bestow photostability on nucleobases and hence preserve the structural integrity of DNA following absorption of ultraviolet (UV) radiation. One controversial recovery mechanism proposed to account for this photostability involves electron-driven proton transfer (EDPT) in Watson–Crick base pairs. The first direct observation is reported of the EDPT process after UV excitation of individual guanine–cytosine (G⋅C) Watson–Crick base pairs by ultrafast time-resolved UV/visible and mid-infrared spectroscopy. The formation of an intermediate biradical species (G[−H]⋅C[+H]) with a lifetime of 2.9 ps was tracked. The majority of these biradicals return to the original G⋅C Watson–Crick pairs, but up to 10 % of the initially excited molecules instead form a stable photoproduct G*⋅C* that has undergone double hydrogen-atom transfer. The observation of these sequential EDPT mechanisms across intermolecular hydrogen bonds confirms an important and long debated pathway for the deactivation of photoexcited base pairs, with possible implications for the UV photochemistry of DNA.
BibTeX:
@article{Roettger2015,
author = {Katharina Röttger and Hugo J. B. Marroux and Michael P. Grubb and Philip M. Coulter and Hendrik Böhnke and Alexander S. Henderson and M. Carmen Galan and Friedrich Temps and Andrew J. Orr-Ewing and Gareth M. Roberts},
title = {Ultraviolet Absorption Induces Hydrogen-Atom Transfer in G⋅C Watson-Crick DNA Base Pairs in Solution},
journal = {Angewandte Chemie International Edition},
publisher = {Wiley-Blackwell},
year = {2015},
volume = {54},
number = {49},
pages = {14719--14722},
doi = {https://doi.org/10.1002/anie.201506940}
}
Thermal and Light-Induced Spin Transitions of FeIIComplexes with 4- and 5-(Phenylazo)-2,2′-bipyridine Ligands: Intra- vs. Intermolecular Effects
S.O. Schmidt, H. Naggert, A. Buchholz, H. Brandenburg, A. Bannwarth, W. Plass and F. Tuczek, Eur. J. Inorg. Chem. 2015, 2016, 2175-2186.
Abstract:
Five new spin crossover complexes with 4- and 5-(phenylazo)-2,2-bipyridine (4-/5-PAbipy) ligands were synthesized and investigated with respect to their spin crossover (SCO) behavior. The results are compared to the thermal and light-induced spin transition properties of the parent SCO complexes [Fe(bpz)2(bipy)] (1) and [Fe(bipy)2(NCS)2] (2). [Fe(bpz)2(4-PAbipy)] (1a) undergoes a stepwise spin transition whereas [Fe(bpz)2(5-PAbipy)] (1b) exhibits a one-step transition with a 6 K-wide hysteresis. For [Fe(bpz)2(tBu5-PAbipy)] (1c) the spin transition to the low-spin state is incomplete. Qualitatively similar changes of the SCO behavior are observed for the complexes [Fe(4-PAbipy)2(NCS)2] (2a) and [Fe(5-PAbipy)2(NCS)2] (2b). In comparison to the parent system 2, a strengthening of intermolecular interactions leads to a stabilization of the low-spin state. Evidence for the LIESST behavior could be obtained for all new compounds by means of magnetic susceptibility measurements as well as UV/Vis and resonance Raman spectroscopy.
BibTeX:
@article{Schmidt2015,
author = {Sven Olaf Schmidt and Holger Naggert and Axel Buchholz and Hannah Brandenburg and Alexander Bannwarth and Winfried Plass and Felix Tuczek},
title = {Thermal and Light-Induced Spin Transitions of FeIIComplexes with 4- and 5-(Phenylazo)-2,2′-bipyridine Ligands: Intra- vs. Intermolecular Effects},
journal = {Eur. J. Inorg. Chem.},
publisher = {Wiley-Blackwell},
year = {2015},
volume = {2016},
number = {13-14},
pages = {2175--2186},
doi = {https://doi.org/10.1002/ejic.201501252}
}
Light-induced conductance switching in azobenzene based near-percolated single wall carbon nanotube/polymer composites
V. Schneider, T. Strunskus, M. Elbahri and F. Faupel, Carbon 2015, 90, 94–101.
Abstract:
Photochromic molecular switches are a class of organic molecules that allow a reversible control over molecular structure, dipole moment, or conductivity with light. Incorporating these chromophores into polymer composites provides the possibility to photoswitch intrinsic properties of these materials. Here we report reversible light-induced conductance switching of near-percolated single wall carbon nanotube/polymethylmethacrylate (SWCNT/PMMA) nanocomposites containing azobenzene derivatives that do not exhibit molecular conductance switching. Stable switching amplitudes up to 28% were achieved near the percolation threshold. The results suggest a Pool–Frenkel type conduction mechanism where the chromophores are an integral part of the conduction path.
BibTeX:
@article{Schneider2015,
author = {Schneider, V. and Strunskus, T. and Elbahri, M. and Faupel, F.},
title = {Light-induced conductance switching in azobenzene based near-percolated single wall carbon nanotube/polymer composites},
journal = {Carbon},
year = {2015},
volume = {90},
pages = {94–101},
doi = {https://doi.org/10.1016/j.carbon.2015.04.002}
}
Pinpointing mechanochemical bond dissociation with the aid of a safety line
D. Schütze, K. Holz, J. Müller, M.K. Beyer, U. Lüning and B. Hartke, Angew. Chem. 2015, 127, 2587-2590.
Abstract:
Mechanophores contain a mechanically labile bond that can be broken by an external mechanical force. Mechanical activation is often applied via ultrasound, yielding qualitative information on the applied force. Quantitative measurement and control of the applied force is possible via atomic force microscopy (AFM). Here we present the synthesis of a macrocycle containing both the mechanophore and an aliphatic chain that acts as a safety line upon bond breaking. This ring-opening mechanophore unit is linked to poly(ethylene glycol) spacers, which afford investigation by single molecule force spectroscopy with an AFM. The length increase upon rupture of the molecule is measured and compared with quantum chemical calculations. With this approach, arbitrary weak bonds can be quantitatively investigated, and ring-opening mechanophores can be taylored with respect to the desired rupture force as well as the desired length increase upon bond rupture.
BibTeX:
@article{Schuetze2015,
author = {Schütze, D. and Holz, K. and Müller, J. and Beyer, M. K. and Lüning, U. and Hartke, B.},
title = {Pinpointing mechanochemical bond dissociation with the aid of a safety line},
journal = {Angew. Chem.},
year = {2015},
volume = {127},
pages = {2587-2590},
doi = {https://doi.org/10.1002/ange.201409691}
}
Electronic and Vibrational States of Single Tin–Phthalocyanine Molecules in Double Layers on Ag(111)
F. Schwarz, Y.F. Wang, W.A. Hofer, R. Berndt, E. Runge and J. Kröger, The Journal of Physical Chemistry C 2015, 119, 15716–15722.
Abstract:
Electronic and vibrational properties of the two stable molecular configurations of Sn–phthalocyanine adsorbed on an ultrathin Sn–phthalocyanine buffer film on Ag(111) have been investigated with scanning tunneling microscopy and density functional calculations. Complex submolecular patterns are experimentally observed in unoccupied states images. The calculations show that they result from a superposition of Sn p orbitals. Furthermore, the characteristic features in spectra of the differential conductance are reproduced by the calculations together with a remarkable difference between the two configurations. First-principles calculations show that rather than a single vibrational mode and its higher harmonics the excitations of different molecular vibrational quanta induce replica of orbital spectroscopic signatures. The replicated orbital features appear for the configuration with a low molecule–surface coupling. To model spectra of molecules with a larger coupling to the surface it is sufficient to consider elastic tunneling to orbital resonances alone.
BibTeX:
@article{Schwarz2015,
author = {Schwarz, F. and Wang, Y. F. and Hofer, W. A. and Berndt, R. and Runge, E. and Kröger, J.},
title = {Electronic and Vibrational States of Single Tin–Phthalocyanine Molecules in Double Layers on Ag(111)},
journal = {The Journal of Physical Chemistry C},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {119},
number = {27},
pages = {15716–15722},
doi = {https://doi.org/10.1021/acs.jpcc.5b03392}
}
High Yielding Lithiation of Azobenzenes by Tin-Lithium Exchange
J. Strueben, M. Lipfert, J.-O. Springer, C.A. Gould, P.J. Gates, F.D. Sönnichsen and A. Staubitz, Chem. Eur. J. 2015, 21, 11165-11173.
Abstract:
The lithiation of halogenated azobenzenes by a halogen-lithium exchange commonly leads to a substantial degradation of the azo-group to give hydrazine derivatives besides the desired aryl-lithium species. Yields for quenching reactions with electrophiles are therefore low. This work shows that a transmetalation reaction of easily accessible stannylated azobenzenes with methyl lithium leads to a near-quantitative lithiation of azobenzenes in para, meta and ortho position. To investigate the scope of the reaction, various lithiated azobenzenes species were quenched with a variety of 119 electrophiles. Furthermore, mechanistic Sn NMR spectroscopic studies on the formation of lithiated azobenzenes are presented. A tin-ate complex of the azobenzene could be detected at low temperatures. The findings from this study are supported by DFT calculations.
BibTeX:
@article{Strueben2015,
author = {Strueben, Jan and Lipfert, Matthias and Springer, Jan-Ole and Gould, Colin A. and Gates, Paul J. and Sönnichsen, Frank D. and Staubitz, Anne},
title = {High Yielding Lithiation of Azobenzenes by Tin-Lithium Exchange},
journal = {Chem. Eur. J.},
year = {2015},
volume = {21},
pages = {11165-11173},
doi = {https://doi.org/10.1002/chem.201500003}
}
X-ray spectroscopy characterization of azobenzene-functionalized triazatriangulenium adlayers on Au(111) surfaces
S. Ulrich, U. Jung, T. Strunskus, C. Schütt, A. Bloedorn, S. Lemke, E. Ludwig, L. Kipp, F. Faupel, O. Magnussen and R. Herges, Phys. Chem. Chem. Phys. 2015, 17, 17053–17062.
Abstract:
Triazatriangulenium (TATA) platform molecules allow the preparation of functionalized surfaces with well-defined lateral spacings of freestanding functional groups. Using scanning tunneling microscopy, synchrotron-based X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy and complementary density functional theory calculations the chemical composition and orientational order of adlayers of functionalized azobenzene containing TATA platform molecules were characterized. According to these studies the molecules are chemically intact on the surface after self-assembly from solution and exhibit a well-defined adsorption geometry where the azobenzene units are oriented almost perpendicular to the surface.
BibTeX:
@article{Ulrich2015,
author = {Ulrich, Sandra and Jung, Ulrich and Strunskus, Thomas and Schütt, Christian and Bloedorn, Andreas and Lemke, Sonja and Ludwig, Eric and Kipp, Lutz and Faupel, Franz and Magnussen, Olaf and Herges, Rainer},
title = {X-ray spectroscopy characterization of azobenzene-functionalized triazatriangulenium adlayers on Au(111) surfaces},
journal = {Phys. Chem. Chem. Phys.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2015},
volume = {17},
number = {26},
pages = {17053–17062},
doi = {https://doi.org/10.1039/c5cp01447f}
}
Low-temperature scanning tunneling microscopy study on the electronic properties of a double-decker DyPc 2 molecule at the surface
Y. Zhang, P. Liao, J. Kan, C. Yin, N. Li, J. Liu, Q. Chen, Y. Wang, W. Chen, G.Q. Xu, J. Jiang, R. Berndt and K. Wu, Phys. Chem. Chem. Phys. 2015, 17, 27019-27026.
Abstract:
To fully achieve potential applications of the double-decker molecules containing rare earth elements as single-molecule magnets in molecular spintronics, it is crucial to understand the 4f states of the rare earth atoms sandwiched in the double-decker molecules by metal electrodes. In this study, low-temperature scanning tunneling microscopy and spectroscopy were employed to investigate the isolated double-decker DyPc2 molecule adsorbed on Au(111) via its differential conductance measurements. The experimental results revealed that the differential conductance maps acquired at a constant height mode simply depicted the authentic molecular orbitals; moreover, the differential conductance maps achieved at a constant current mode could not directly probe the 4f states of the sandwiched Dy atom. This was consistent with the spectra obtained over the molecule center around the Fermi level, indicative of no Kondo feature. Upon decreasing the tip-molecule distance, the CH-mode images presented high-resolution structure but no information of the 4f states. All results indicated that the Dy atom barely contributed to the tunneling current because of the absence of coupling with the microscope tip, echoing the inaccessibility of the Dy 4f states in the double-decker DyPc2 molecule.
BibTeX:
@article{Zhang2015,
author = {Yajie Zhang and Peilin Liao and Jinglan Kan and Cen Yin and Na Li and Jing Liu and Qiwei Chen and Yongfeng Wang and Wei Chen and Guo Qin Xu and Jianzhuang Jiang and Richard Berndt and Kai Wu},
title = {Low-temperature scanning tunneling microscopy study on the electronic properties of a double-decker DyPc 2 molecule at the surface},
journal = {Phys. Chem. Chem. Phys.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2015},
volume = {17},
number = {40},
pages = {27019--27026},
doi = {https://doi.org/10.1039/c5cp03925h}
}
Femtosecond spectroscopy reveals huge differences in the photoisomerisation dynamics between azobenzenes linked to polymers and azobenzenes in solution
J. Bahrenburg, F. Renth, F. Temps, F. Plamper and W. Richtering, Phys. Chem. Chem. Phys. 2014, 16, 11549-11554.
Abstract:
Femtosecond fluorescence up-conversion spectroscopy of two azobenzenes covalently attached to the side chain or linked by covalent bonds at each end into the main chain of polybutylmethacrylate polymer colloids with different cross-linking ratios reveals dramatic differences in the excited-state dynamics compared to the monomer chromophores in solution due to strong mechanical forces in the complex micronetworks. For the azobenzene derivative DR1 in the polymer side chain, the measurements determined an increase of the mean excited-state lifetime after irradiation at [small lambda] = 475 nm to ?[small tau]? = 5.5 ps from ?[small tau]? = 0.5 ps for the monomer. For the cross-linked BAAB in the polymer main chain, an increase of ?[small tau]? was found of more than a factor-of-20. Moreover, with a lifetime of [small tau] = 430 ps, [approximate]12% of the molecules in the tightly (1 : 10) cross-linked polymer were found to remain in the excited state about 100 times longer than observed for the monomer chromophore. These results are of high relevance for applications of photoswitchable polymer materials.
BibTeX:
@article{Bahrenburg2014a,
author = {Bahrenburg, Julia and Renth, Falk and Temps, Friedrich and Plamper, Felix and Richtering, Walter},
title = {Femtosecond spectroscopy reveals huge differences in the photoisomerisation dynamics between azobenzenes linked to polymers and azobenzenes in solution},
journal = {Phys. Chem. Chem. Phys.},
year = {2014},
volume = {16},
pages = {11549-11554},
doi = {https://doi.org/10.1039/C4CP01196A}
}
Ultrafast Dynamics of a Bistable Intramolecular Proton Transfer Switch
J. Bahrenburg, M.F. Rode, A.L. Sobolewski and F. Temps, in: 19th International Conference on Ultrafast Phenomena 2014 09.Wed.P3.20.
Abstract:
The stepwise formation of the proton transfer product of a bistable molecular switch was unambiguously revealed by femtosecond fluorescence and absorption spectroscopy. The interpretation was supported by ab initio excited-state calculations.
BibTeX:
@inproceedings{Bahrenburg2014,
author = {Julia Bahrenburg and Michal F. Rode and Andrzej L. Sobolewski and Friedrich Temps},
title = {Ultrafast Dynamics of a Bistable Intramolecular Proton Transfer Switch},
booktitle = {19th International Conference on Ultrafast Phenomena},
journal = {19th International Conference on Ultrafast Phenomena},
publisher = {Optical Society of America},
year = {2014},
pages = {09.Wed.P3.20},
doi = {https://doi.org/10.1364/UP.2014.09.Wed.P3.20}
}
Tunneling anisotropic magnetoresistance effect of single adatoms on a noncollinear magnetic surface
N.M. Caffrey, S. Schröder, P. Ferriani and S. Heinze, J. Phys.: Condens. Matter 2014, 26, 394010.
Abstract:
The tunneling anisotropic magnetoresistance (TAMR) effect demonstrates the sensitivity of spin-polarized electron transport to the orientation of the magnetization with respect to the crystallographic axes. As the TAMR effect requires only a single magnetic electrode, in contrast to the tunneling magnetoresistance effect, it offers an attractive route to alternative spintronic applications. In this work we consider the TAMR effect at the single-atom limit by investigating the anisotropy of the local density of states (LDOS) in the vacuum above transition-metal adatoms adsorbed on a noncollinear magnetic surface, the monolayer of Mn on W(1 1 0). This surface presents a cycloidal spin spiral ground state with an angle of 173° between neighboring spins and thus allows a quasi-continuous exploration of the angular dependence of the TAMR of adsorbed adatoms using scanning tunneling microscopy. Using first-principle calculations, we investigate the TAMR of Co, Rh and Ir adatoms on Mn/W(1 1 0) and relate our results to the magnetization-direction-dependent changes in the LDOS. The anisotropic effect is found to be enhanced dramatically on the adsorption of heavy transition-metal atoms, with values of up to 50% predicted from our calculations. This effect will be measurable even with a non-magnetic STM tip.
BibTeX:
@article{Caffrey2014,
author = {Caffrey, Nuala M and Schröder, Silke and Ferriani, Paolo and Heinze, Stefan},
title = {Tunneling anisotropic magnetoresistance effect of single adatoms on a noncollinear magnetic surface},
journal = {J. Phys.: Condens. Matter},
year = {2014},
volume = {26},
pages = {394010},
doi = {https://doi.org/10.1088/0953-8984/26/39/394010}
}
Synthesis and surface-spectroscopic characterization of photoisomerizable glyco-SAMs on Au(111)
V. Chandrasekaran, H. Jacob, F. Petersen, K. Kathirvel, F. Tuczek and T.K. Lindhorst, Chem. Eur. J. 2014, 20, 8744-8752.
Abstract:
Photoisomerizable glyco-SAMs (self-assembled monolayers), utilizing synthetic azobenzene glycoside derivatives were fabricated. The ultimate goal of this project is to assay the influence of the 3D arrangement of sugar ligands on cell adhesion, and eventually make cell adhesion photoswitchable. However, it is a prerequisite for any biological study on the spatial conditions of carbohydrate recognition, that photoisomerization of the surface molecules can be verified. Here, we employed IRRAS and XPS to spectroscopically characterize glyco-SAMs. In particular and unprecedented to date, we prove reversible EZE isomerization of azobenzene glycoside-terminated SAMs.
BibTeX:
@article{Chandrasekaran2014,
author = {Chandrasekaran, V. and Jacob, H. and Petersen, F. and Kathirvel, K. and Tuczek, F. and Lindhorst, T. K.},
title = {Synthesis and surface-spectroscopic characterization of photoisomerizable glyco-SAMs on Au(111)},
journal = {Chem. Eur. J.},
year = {2014},
volume = {20},
pages = {8744-8752},
doi = {https://doi.org/10.1002/chem.201402075}
}
Synthesis and Photochromic Properties of Configurationally Varied Azobenzene Glycosides
V. Chandrasekaran, E. Johannes, H. Kobarg, F.D. Sönnichsen and T.K. Lindhorst, ChemistryOpen 2014, 3, 99-108.
Abstract:
Spatial orientation of carbohydrates is a meaningful parameter in carbohydrate recognition processes. To vary orientation of sugars with temporal and spatial resolution, photosensitive glycoconjugates with favorable photochromic properties appear to be opportune. Here, a series of azobenzene glycosides were synthesized, employing glycoside synthesis and Mills reaction, to allow “switching” of carbohydrate orientation by reversible E/Z isomerization of the azobenzene N=N double bond. Their photochromic properties were tested and effects of azobenzene substitution as well as the effect of anomeric configuration and the orientation of the sugars 2-hydroxy group were evaluated.
BibTeX:
@article{Chandrasekaran2014a,
author = {Chandrasekaran, Vijayanand and Johannes, Eugen and Kobarg, Hauke and Sönnichsen, Frank D. and Lindhorst, Thisbe K.},
title = {Synthesis and Photochromic Properties of Configurationally Varied Azobenzene Glycosides},
journal = {ChemistryOpen},
year = {2014},
volume = {3},
number = {3},
pages = {99-108},
doi = {https://doi.org/10.1002/open.201402010}
}
Coordination-Induced Spin-State-Switch (CISSS) in water
M. Dommaschk, F. Gutzeit, S. Boretius, R. Haag and R. Herges, Chem. Commun. 2014, 50, 12476-12478.
Abstract:
We present a non-ionic water-soluble porphyrin that does not exhibit measurable aggregation even at high concentrations in water. The spin state of the corresponding nickel(II) complex changes from completely diamagnetic (low-spin) to paramagnetic (high-spin) upon addition of a strong axial ligand. This leads to a strongly reduced NMR relaxation time of the water protons even at low concentrations of the complex.
BibTeX:
@article{Dommaschk2014,
author = {Dommaschk, Marcel and Gutzeit, Florian and Boretius, Susann and Haag, Rainer and Herges, Rainer},
title = {Coordination-Induced Spin-State-Switch (CISSS) in water},
journal = {Chem. Commun.},
year = {2014},
volume = {50},
pages = {12476-12478},
doi = {https://doi.org/10.1039/c4cc05525j}
}
Rational Design of a Room Temperature Molecular Spin Switch. The Light-Driven Coordination Induced Spin State Switch (LD-CISSS) Approach.
M. Dommaschk, C. Schutt, S. Venkataramani, U. Jana, C. Nather, F.D. Soennichsen and R. Herges, Dalton Trans. 2014, 43, 17395-17405.
Abstract:
Extensive use of quantum chemical calculations has been made to rationally design a molecule whose spin state can be switched reversibly using light of two different wavelengths at room temperature in solution. Spin change is induced by changing the coordination number of a nickel complex. The coordination number in turn is switched using a photochromic ligand that binds in one configuration and dissociates in the other. We demonstrate that successful design relies on a precise geometry fit and delicate electronic tuning. Our designer complex exhibits an extremely high long-term switching stability (more than 20,000 cycles) and a high switching efficiency. The high-spin state is extraordinarily stable with a half-life of 400 days at room temperature. Switching between the dia- and paramagnetic state is achieved with visible light (500 and 430 nm). The compound can also be used as a molecular logic gate with light and pH as input and the magnetic state as non-destructive read-out.
BibTeX:
@article{Dommaschk2014a,
author = {Dommaschk, Marcel and Schutt, Christian and Venkataramani, Sugumar and Jana, Umasish and Nather, Christian and Soennichsen, Frank D and Herges, Rainer},
title = {Rational Design of a Room Temperature Molecular Spin Switch. The Light-Driven Coordination Induced Spin State Switch (LD-CISSS) Approach.},
journal = {Dalton Trans.},
year = {2014},
volume = {43},
pages = {17395-17405},
doi = {https://doi.org/10.1039/C4DT03048F}
}
Effective Optical Properties of Plasmonic Nanocomposites
C. Etrich, S. Fahr, M.K. Hedayati, F. Faupel, M. Elbahri and C. Rockstuhl, Materials 2014, 7, 727-741.
Abstract:
Plasmonic nanocomposites find many applications, such as nanometric coatings in emerging fields, such as optotronics, photovoltaics or integrated optics. To make use of their ability to affect light propagation in an unprecedented manner, plasmonic nanocomposites should consist of densely packed metallic nanoparticles. This causes a major challenge for their theoretical description, since the reliable assignment of effective optical properties with established effective medium theories is no longer possible. Established theories, e.g., the Maxwell-Garnett formalism, are only applicable for strongly diluted nanocomposites. This effective description, however, is a prerequisite to consider plasmonic nanocomposites in the design of optical devices. Here, we mitigate this problem and use full wave optical simulations to assign effective properties to plasmonic nanocomposites with filling fractions close to the percolation threshold. We show that these effective properties can be used to properly predict the optical action of functional devices that contain nanocomposites in their design. With this contribution we pave the way to consider plasmonic nanocomposites comparably to ordinary materials in the design of optical elements.
BibTeX:
@article{Etrich2014,
author = {Etrich, Christoph and Fahr, Stephan and Hedayati, Mehdi Keshavarz and Faupel, Franz and Elbahri, Mady and Rockstuhl, Carsten},
title = {Effective Optical Properties of Plasmonic Nanocomposites},
journal = {Materials},
year = {2014},
volume = {7},
number = {2},
pages = {727-741},
doi = {https://doi.org/10.3390/ma7020727}
}
MOCVD of Fe atoms on H/Si(111) surfaces using Fe-phthalocyanine
M. Gruyters, T. Pingel and R. Berndt, Applied Physics A 2014, 114, 363-366.
Abstract:
Single Fe atoms are deposited on hydrogen-passivated Si(111) surfaces by decomposition of FePc molecules. The metal-organic molecules are evaporated from powder in a heated crucible of an electron beam source. Scanning tunneling microscopy (STM) indicates the incorporation of the central Fe atom of the molecule into H/Si(111) in the near-surface region. This provides a possible precursor state for implantation deeper into the semiconductor substrate.
BibTeX:
@article{Gruyters2014,
author = {Gruyters, Markus and Pingel, Torben and Berndt, Richard},
title = {MOCVD of Fe atoms on H/Si(111) surfaces using Fe-phthalocyanine},
journal = {Applied Physics A},
year = {2014},
volume = {114},
number = {2},
pages = {363-366},
doi = {https://doi.org/10.1007/s00339-013-8177-2}
}
The hybrid concept for realization of an ultra-thin plasmonic metamaterial antireflection coating and plasmonic rainbow
M.K. Hedayati, S. Fahr, C. Etrich, F. Faupel, C. Rockstuhl and M. Elbahri, Nanoscale 2014, 6, 6037-6045.
Abstract:
We report on the design, simulation, fabrication, and characterization of a novel two layer anti-reflective coating (ARC) based on a plasmonic metamaterial and a dielectric. Promoted by the strong material dispersion of the plasmonic metamaterial, our novel concept (called hybrid ARC) combines two possible arrangements for layers in an anti-reflection coating into a single structure; albeit at two different wavelengths. This, however, causes a broadband reduction of reflection that is less sensitive against oblique incidence when compared to traditional antireflective coatings. Furthermore, we show that the current metamaterial on a metal reflector can be used for the visualization of different coloration such as plasmonic rainbow despite its sub-wavelength thickness.
BibTeX:
@article{Hedayati2014b,
author = {Hedayati, M. Keshavarz and Fahr, S. and Etrich, C. and Faupel, F. and Rockstuhl, C. and Elbahri, M.},
title = {The hybrid concept for realization of an ultra-thin plasmonic metamaterial antireflection coating and plasmonic rainbow},
journal = {Nanoscale},
year = {2014},
volume = {6},
pages = {6037-6045},
doi = {https://doi.org/10.1039/C4NR00087K}
}
Review of Plasmonic Nanocomposite Metamaterial Absorber
M.K. Hedayati, F. Faupel and M. Elbahri, Materials 2014, 7, 1221-1248.
Abstract:
Plasmonic metamaterials are artificial materials typically composed of noble metals in which the features of photonics and electronics are linked by coupling photons to conduction electrons of metal (known as surface plasmon). These rationally designed structures have spurred interest noticeably since they demonstrate some fascinating properties which are unattainable with naturally occurring materials. Complete absorption of light is one of the recent exotic properties of plasmonic metamaterials which has broadened its application area considerably. This is realized by designing a medium whose impedance matches that of free space while being opaque. If such a medium is filled with some lossy medium, the resulting structure can absorb light totally in a sharp or broad frequency range. Although several types of metamaterials perfect absorber have been demonstrated so far, in the current paper we overview (and focus on) perfect absorbers based on nanocomposites where the total thickness is a few tens of nanometer and the absorption band is broad, tunable and insensitive to the angle of incidence. The nanocomposites consist of metal nanoparticles embedded in a dielectric matrix with a high filling factor close to the percolation threshold. The filling factor can be tailored by the vapor phase co-deposition of the metallic and dielectric components. In addition, novel wet chemical approaches are discussed which are bio-inspired or involve synthesis within levitating Leidenfrost drops, for instance. Moreover, theoretical considerations, optical properties, and potential application of perfect absorbers will be presented.
BibTeX:
@article{Hedayati2014,
author = {Hedayati, Mehdi Keshavarz and Faupel, Franz and Elbahri, Mady},
title = {Review of Plasmonic Nanocomposite Metamaterial Absorber},
journal = {Materials},
year = {2014},
volume = {7},
number = {2},
pages = {1221-1248},
doi = {https://doi.org/10.3390/ma7021221}
}
Photo-driven Super Absorber as an Active Metamaterial with a Tunable Molecular-Plasmonic Coupling
M.K. Hedayati, M. Javaheri, A.U. Zillohu, H.J. El-Khozondar, M.S. Bawa'aneh, A. Lavrinenko, F. Faupel and M. Elbahri, Advanced Optical Materials 2014, 2, 705-710.
Abstract:
An optically driven metamaterial with a photoswitchable weak and strong molecular-plasmonic coupling is demonstrated. In this active perfect absorber, the absorption band can be broadened more than 150 nm (split with an energy difference of 780 meV) by UV irradiation, which demonstrates a new class of optically tunable metamaterial absorber for visible frequencies.
BibTeX:
@article{Hedayati2014c,
author = {Hedayati, Mehdi Keshavarz and Javaheri, Mojtaba and Zillohu, Ahnaf Usman and El-Khozondar, Hala Jarallah and Bawa'aneh, Muhammad S. and Lavrinenko, Andrei and Faupel, Franz and Elbahri, Mady},
title = {Photo-driven Super Absorber as an Active Metamaterial with a Tunable Molecular-Plasmonic Coupling},
journal = {Advanced Optical Materials},
year = {2014},
volume = {2},
pages = {705-710},
doi = {https://doi.org/10.1002/adom.201400105}
}
Plasmonic tunable metamaterial absorber as ultraviolet protection film
M.K. Hedayati, A.U. Zillohu, T. Strunskus, F. Faupel and M. Elbahri, Applied Physics Letters 2014, 104, 041103.
Abstract:
Plasmonic metamaterials designed for optical frequency have to be shrunk down to few 10th of nanometer which turns their manufacturing cumbersome. Here, we shift the performance of metamaterial down to ultraviolet (UV) by using ultrathin nanocomposite as a tunable plasmonic metamaterial fabricated with tandem co-deposition. It provides the possibility to realize a plasmonic metamaterial absorber for UV frequency with marginal angle sensitivity. Its resonance frequency and intensity can be adjusted by changing thickness and filling factor of the composite. Presented approach for tunable metamaterials for high frequency could pave the way for their application for thermo-photovoltaic, stealth technology, and UV-protective coating.
BibTeX:
@article{Hedayati2014a,
author = {Hedayati, M. K. and Zillohu, A. U. and Strunskus, T. and Faupel, F. and Elbahri, M.},
title = {Plasmonic tunable metamaterial absorber as ultraviolet protection film},
journal = {Applied Physics Letters},
year = {2014},
volume = {104},
number = {4},
pages = {041103},
doi = {https://doi.org/10.1063/1.4863202}
}
Adhesion tilt-tolerance in bio-inspired mushroom-shaped adhesive microstructure
L. Heepe, G. Carbone, E. Pierro, A.E. Kovalev and S.N. Gorb, Applied Physics Letters 2014, 104, 011906.
Abstract:
We studied experimentally and theoretically the effect of different tilt angles on the adhesion of mushroom-shaped adhesive microstructures. The marginal measured influence of tilting on pull-off forces is quantitatively well confirmed by numerical and theoretical calculations and was shown to be a direct consequence of an optimized stress distribution. In addition, the presence of a joint-like narrowing under the contact elements, as found in some biological attachment systems, was shown to further contribute to the tilt-tolerance. The results obtained allow us to explain the advantage of the widely observed mushroom-shaped contact geometry in nature for long-term and permanent adhesion.
BibTeX:
@article{Heepe2014,
author = {Heepe, Lars and Carbone, Giuseppe and Pierro, Elena and Kovalev, Alexander E. and Gorb, Stanislav N.},
title = {Adhesion tilt-tolerance in bio-inspired mushroom-shaped adhesive microstructure},
journal = {Applied Physics Letters},
year = {2014},
volume = {104},
pages = {011906},
doi = {https://doi.org/10.1063/1.4860991}
}
Biologically Inspired Mushroom-Shaped Adhesive Microstructures
L. Heepe and S. Gorb, Annual Review of Materials Research 2014, 44, 173-203.
Abstract:
Adhesion is a fundamental phenomenon with great importance in technology, in our everyday life, and in nature. In this article, we review physical interactions that resist the separation of two solids in contact. By using examples of biological attachment systems, we summarize and categorize various principles that contribute to the so-called gecko effect. Emphasis is placed on the contact geometry and in particular on the mushroom-shaped geometry, which is observed in long-term biological adhesive systems. Furthermore, we report on artificial model systems with this bio-inspired geometry and demonstrate that surface microstructures with this geometry are promising candidates for technical applications, in which repeatable, reversible, and residue-free adhesion under different environmental conditions—such as air, fluid, and vacuum—is required. Various applications in robotic systems and in industrial pick-and-place processes are discussed. Expected final online publication date for the Annual Review of Materials Research Volume 44 is July 01, 2014. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
BibTeX:
@article{Heepe2014b,
author = {Heepe, Lars and Gorb, Stanislav},
title = {Biologically Inspired Mushroom-Shaped Adhesive Microstructures},
journal = {Annual Review of Materials Research},
year = {2014},
volume = {44},
pages = {173-203},
doi = {https://doi.org/10.1146/annurev-matsci-062910-100458}
}
Haftung bewahren
L. Heepe and S.N. Gorb, Physik in unserer Zeit 2014, 45, 7-8.
Abstract:
Haftung ist ein bedeutender Effekt sowohl in Technik und Alltag wie auch in der Natur. Ein interdisziplinäres Forscherteam der Universität Kiel hat herausgefunden, dass das Geheimnis, der in der Natur weit verbreiteten discoidalen Geometrie der Haftorgane, in einer gleichmäßigen mechanischen Spannungsverteilung zwischen Oberfläche und Haftelement liegt.
BibTeX:
@article{Heepe2014a,
author = {Heepe, Lars and Gorb, Stanislav N.},
title = {Haftung bewahren},
journal = {Physik in unserer Zeit},
year = {2014},
volume = {45},
pages = {7-8},
doi = {https://doi.org/10.1002/piuz.201490013}
}
A Shuttle for the Transport of Protons Based on a [2]Rotaxane
B. Hesseler, M. Zindler, R. Herges and U. Lüning, European Journal of Organic Chemistry 2014, 3885-3901.
Abstract:
A [2]rotaxane shuttle for (light-driven) proton transport has been designed and synthesized. The rotaxane contains a macrocyclic ring that carries a pyridine nitrogen atom as a basic center to bind and to transport a proton. The axis includes an amide binding site for the macrocycle and a positive charge in close vicinity. Upon protonation of the pyridine nitrogen atom, the hydrogen bond is broken and Coulomb repulsion between the protonated pyridine and the permanent positive charge in the axis pushes the protonated macrocycle to the other end of the axis. By variation of the pH the ring can shuttle to and fro. Its locations on the axis were determined by NMR spectroscopy.
BibTeX:
@article{Hesseler2014,
author = {Hesseler, Britta and Zindler, Melanie and Herges, Rainer and Lüning, Ulrich},
title = {A Shuttle for the Transport of Protons Based on a [2]Rotaxane},
journal = {European Journal of Organic Chemistry},
year = {2014},
pages = {3885-3901},
doi = {https://doi.org/10.1002/ejoc.201402249}
}
Nanocomposite Electrospun Nanofiber Membranes for Environmental Remediation
S. Homaeigohar and M. Elbahri, Materials 2014, 7, 1017-1045.
Abstract:
Rapid worldwide industrialization and population growth is going to lead to an extensive environmental pollution. Therefore, so many people are currently suffering from the water shortage induced by the respective pollution, as well as poor air quality and a huge fund is wasted in the world each year due to the relevant problems. Environmental remediation necessitates implementation of novel materials and technologies, which are cost and energy efficient. Nanomaterials, with their unique chemical and physical properties, are an optimum solution. Accordingly, there is a strong motivation in seeking nano-based approaches for alleviation of environmental problems in an energy efficient, thereby, inexpensive manner. Thanks to a high porosity and surface area presenting an extraordinary permeability (thereby an energy efficiency) and selectivity, respectively, nanofibrous membranes are a desirable candidate. Their functionality and applicability is even promoted when adopting a nanocomposite strategy. In this case, specific nanofillers, such as metal oxides, carbon nanotubes, precious metals, and smart biological agents, are incorporated either during electrospinning or in the post-processing. Moreover, to meet operational requirements, e.g., to enhance mechanical stability, decrease of pressure drop, etc., nanofibrous membranes are backed by a microfibrous non-woven forming a hybrid membrane. The novel generation of nanocomposite/hybrid nanofibrous membranes can perform extraordinarily well in environmental remediation and control. This reality justifies authoring of this review paper.
BibTeX:
@article{Homaeigohar2014,
author = {Homaeigohar, Shahin and Elbahri, Mady},
title = {Nanocomposite Electrospun Nanofiber Membranes for Environmental Remediation},
journal = {Materials},
year = {2014},
volume = {7},
number = {2},
pages = {1017-1045},
doi = {https://doi.org/10.3390/ma7021017}
}
Monitoring the reversible photoisomerization of an azobenzene-functionalized molecular triazatriangulene platform on Au(111) by IRRAS
H. Jacob, S. Ulrich, U. Jung, S. Lemke, T. Rusch, C. Schütt, F. Petersen, T. Strunskus, O. Magnussen, R. Herges and F. Tuczek, Phys. Chem. Chem. Phys. 2014, 16, 22643-22650.
Abstract:
Spectroscopic evidence of a reversible, photoinduced trans ↔ cis photoisomerization is provided for an azobenzene-functionalized triazatriangulene (TATA) platform on Au(111). As shown by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), these molecules form a well-ordered self-assembled monolayer (SAM) on Au(111). The surface-adsorbed azo-TATA platforms are also investigated by infrared reflection absorption spectroscopy (IRRAS); a methoxy marker group at the upper phenyl ring of the azo moiety is employed to monitor the switching state. The IRRAS data are analyzed by comparison with theoretical and transmission IR spectra as well as bulk and surface-enhanced Raman spectroscopic (SERS) data. IRRAS shows that the methoxy group is oriented perpendicular to the surface in trans- and tilted with respect to the surface normal in cis-configuration. This indicates that the photoswitching capability of the azobenzene moieties is retained on the gold surface. The lifetime of the cis-configuration is, however, reduced by a factor of 103 with respect to the homogeneous solution.
BibTeX:
@article{Jacob2014,
author = {Jacob, Hanne and Ulrich, Sandra and Jung, Ulrich and Lemke, Sonja and Rusch, Talina and Schütt, Christian and Petersen, Finn and Strunskus, Thomas and Magnussen, Olaf and Herges, Rainer and Tuczek, Felix},
title = {Monitoring the reversible photoisomerization of an azobenzene-functionalized molecular triazatriangulene platform on Au(111) by IRRAS},
journal = {Phys. Chem. Chem. Phys.},
year = {2014},
volume = {16},
pages = {22643-22650},
doi = {https://doi.org/10.1039/c4cp03438d}
}
Challenges and Solutions for Joining Polymer Materials
X. Jin, L. Heepe, J. Strueben, R. Adelung, S.N. Gorb and A. Staubitz, Macromol. Rapid Commun. 2014, 35, 1551-1570.
Abstract:
The fundamental mechanisms of adhesion in general and for polymer-polymer adhesion in particular are being discussed. For this type of adhesion, interdiffusion processes tend to be most important. They depend to a large extent on the miscibility of the polymers. However, for two different low surface energy polymers, this adhesion mechanism does not play a role and more effective methods for achieving adhesion are required. As an alternative to wet chemical treatments or plasma treatments, a novel, facilitated mechanical interlocking process with concave interfacial crystalline fillers is discussed.
BibTeX:
@article{Jin2014,
author = {Jin, Xin and Heepe, Lars and Strueben, Jan and Adelung, Rainer and Gorb, Stanislav N. and Staubitz, Anne},
title = {Challenges and Solutions for Joining Polymer Materials},
journal = {Macromol. Rapid Commun.},
year = {2014},
volume = {35},
pages = {1551-1570},
doi = {https://doi.org/10.1002/marc.201400200}
}
Remotely Triggered Geometrical Isomerization of a Binuclear Complex
S. Karan, T.G. Gopakumar, H. Jacob, S. Meyer, F. Tuczek and R. Berndt, Journal of the American Chemical Society 2014, 136, 6163-6166.
Abstract:
Binuclear organometallic molecules are model systems for investigating intramolecular spin-coupling and charge-transfer processes. Using electrospray ionization, Fe(salten) dimers linked by dipyridyl disulfide are deposited on gold for probing with a low-temperature scanning tunneling microscope. Each monomer constitutes a multistable switch owing to its geometric isomerism. Controlled and reversible remote switching within a single dimer is demonstrated. The process is attributed to intramolecular electron transfer.
BibTeX:
@article{Karan2014,
author = {Karan, Sujoy and Gopakumar, Thiruvancheril G. and Jacob, Hanne and Meyer, Sven and Tuczek, Felix and Berndt, Richard},
title = {Remotely Triggered Geometrical Isomerization of a Binuclear Complex},
journal = {Journal of the American Chemical Society},
year = {2014},
volume = {136},
number = {17},
pages = {6163-6166},
doi = {https://doi.org/10.1021/ja500154g}
}
Synthesis of Functionalized Azobiphenyls and Azoterphenyls with Improved Solubilities for Switching Applications
I. Köhl and U. Lüning, Synthesis 2014, 46, 2376-2382.
Abstract:
Nine new azo compounds, in particular azobiphenyls and azoterphenyls, have been synthesized and their photochemical switching has been investigated. 4,4′-Dihalogenated azobenzenes were generated by oxidative copper-mediated coupling of respective anilines followed by Suzuki–Miyaura cross-coupling reaction. The elongated azobenzenes carry functional groups at the terminal 4-positions and additional methyl substituents at the central benzene rings. While the introduction of two methyl groups improved the solubility of the resulting azo compounds considerably, the introduction of four methyl groups was less successful with respect to solubility. Differences were also found in the photochemical behavior for the dimethyl and the tetramethyl derivatives.
BibTeX:
@article{Koehl2014,
author = {Köhl, I. and Lüning, U.},
title = {Synthesis of Functionalized Azobiphenyls and Azoterphenyls with Improved Solubilities for Switching Applications},
journal = {Synthesis},
year = {2014},
volume = {46},
pages = {2376-2382},
doi = {https://doi.org/10.1055/s-0033-1339028}
}
Photoisomerisation and ligand-controlled reversible aggregation of azobenzene-functionalised gold nanoparticles
A. Kohntopp, A. Dabrowski, M. Malicki and F. Temps, Chem. Commun. 2014, 50, 10105-10107.
Abstract:
The photochemical behaviour of functionalised gold nano-particles (AuNPs) carrying azobenzenethiolate/alkylthiolate monolayers was investigated. Repeated trans-cis and cis-trans isomerisation cycles could be performed in all cases with high efficiency. Reversible photoinduced aggregation was observed when azothiolates with long alkyl spacers ([greater-than-or-equal] C7) were combined with short (C5) alkylthiolate coligands. The choice of coligand thus offers control over the aggregation properties of the nanoparticles.
BibTeX:
@article{Kohntopp2014,
author = {Kohntopp, Anja and Dabrowski, Alexandra and Malicki, Michal and Temps, Friedrich},
title = {Photoisomerisation and ligand-controlled reversible aggregation of azobenzene-functionalised gold nanoparticles},
journal = {Chem. Commun.},
year = {2014},
volume = {50},
pages = {10105-10107},
doi = {https://doi.org/10.1039/C4CC02250E}
}
Determination of Silkworm Silk Fibroin Compressibility Using High Hydrostatic Pressure with in Situ X-ray Microdiffraction
C. Krywka, I. Krasnov, R. Figuli, M. Burghammer and M. Müller, Macromolecules 2014, 47, 7187–7193.
Abstract:
A hydrostatic high pressure cell is used to record pressure resolved wide-angle X-ray microdiffraction data (WAXS) from Bombyx mori silkworm silk fibers with in situ pressurization in the range of 0.01–0.5 GPa (0.1–5 kbar). From the pressure dependent peak positions of (002), (020), (200), and (210) Bragg reflections the (anisotropic) elastic moduli of compression were determined for the different unit cell axes of the crystalline fraction of silk fibroin, comprising of stacked polyalanine β-sheets. The data are compared with X-ray diffraction results previously obtained from silkworm silk at tensile load and spider silk data at high hydrostatic pressure and indicate a different response of the silk fibroin structure to pressure versus tensile load. The response of the unit cell of silkworm silk fibroin to the applied pressure is discussed and modeled taking into account the weak van der Waals bonds between protein β-sheets. Differences are pointed out between the responses of silk’s nanostructure to unidirectional (tensile) load versus the undirected pressure load. Next to the direct determination of the elastic moduli for the different crystal lattice parameters, the pressure response of what is usually referred to as the amorphous phase is also considered.
BibTeX:
@article{Krywka2014,
author = {Krywka, Christina and Krasnov, Igor and Figuli, Roxana and Burghammer, Manfred and Müller, Martin},
title = {Determination of Silkworm Silk Fibroin Compressibility Using High Hydrostatic Pressure with in Situ X-ray Microdiffraction},
journal = {Macromolecules},
year = {2014},
volume = {47},
pages = {7187–7193},
doi = {https://doi.org/10.1021/ma501880h}
}
Triazatriangulenium adlayers on Au(111): Superstructure as a function of alkyl side chain length
S. Lemke, S. Ulrich, F. Claußen, A. Bloedorn, U. Jung, R. Herges and O.M. Magnussen, Surface Science 2014, 632, 71-76.
Abstract:
The structure of organic adlayers, formed by self-assembly of molecular platforms of triazatriangulenium ions on Au(111), was systematically studied by scanning tunneling microscopy as a function of the length of the lateral ligands for alkyl side chains from propyl to dodecyl. A series of hexagonally-ordered adlayers with spacings from 10.7 Å (propyl) to 13.6 Å (dodecyl) was found which are commensurate to the Au(111) substrate lattice, indicating localized bonding of the molecules to the metal.
BibTeX:
@article{Lemke2014,
author = {Lemke, Sonja and Ulrich, Sandra and Claußen, Frauke and Bloedorn, Andreas and Jung, Ulrich and Herges, Rainer and Magnussen, Olaf M.},
title = {Triazatriangulenium adlayers on Au(111): Superstructure as a function of alkyl side chain length},
journal = {Surface Science},
year = {2014},
volume = {632},
pages = {71-76},
doi = {https://doi.org/10.1016/j.susc.2014.08.028}
}
Iron(II) Spin-Crossover Complexes in Ultrathin Films: Electronic Structure and Spin-State Switching by Visible and Vacuum-UV Light
E. Ludwig, H. Naggert, M. Kalläne, S. Rohlf, E. Kröger, A. Bannwarth, A. Quer, K. Rossnagel, L. Kipp and F. Tuczek, Angew. Chem. Int. Ed. 2014, 53, 3019-3023.
Abstract:
The electronic structure of the iron(II) spin crossover complex [Fe(H2bpz)2(phen)] deposited as an ultrathin film on Au(111) is determined by means of UV-photoelectron spectroscopy (UPS) in the high-spin and in the low-spin state. This also allows monitoring the thermal as well as photoinduced spin transition in this system. Moreover, the complex is excited to the metastable high-spin state by irradiation with vacuum-UV light. Relaxation rates after photoexcitation are determined as a function of temperature. They exhibit a transition from thermally activated to tunneling behavior and are two orders of magnitude higher than in the bulk material.
BibTeX:
@article{Ludwig2014,
author = {Ludwig, E. and Naggert, H. and Kalläne, M. and Rohlf, S. and Kröger, E. and Bannwarth, A. and Quer, A. and Rossnagel, K. and Kipp, L. and Tuczek, F.},
title = {Iron(II) Spin-Crossover Complexes in Ultrathin Films: Electronic Structure and Spin-State Switching by Visible and Vacuum-UV Light},
journal = {Angew. Chem. Int. Ed.},
year = {2014},
volume = {53},
pages = {3019-3023},
doi = {https://doi.org/10.1002/anie.201307968}
}
Investigation of optical properties and electronic transitions in bulk and nano-microribbons of molybdenum trioxide
O. Lupan, V. Trofim, V. Cretu, I. Stamov, N.N. Syrbu, I. Tiginyanu, Y.K. Mishra and R. Adelung, Journal of Physics D: Applied Physics 2014, 47, 085302.
Abstract:
In this work, we report on crystalline quality and optical characteristics of molybdenum trioxide (MoO 3 ) bulk and nano-microribbons grown by rapid thermal oxidation (RTO). The developed RTO procedure allows one to synthesize highly crystalline ( α -phase) bulk and nano-microribbons of MoO 3 . For R –Γ indirect transitions in bulk single crystals of MoO 3 , it has been found that the width of the bandgap along the E ‖ c polarization, associated with transitions R v1 –Γ c1 , is lower than the width of the band gap in polarization E ⊥ c , associated with transitions R v2 –Γ c2 . This result is indicative of splitting of the absorption edge due to α -MoO 3 structural anisotropy. Studies of the polarization dependence of the absorption in nano-microribbons ( d ≈ 15–500 nm) demonstrated that the energy gap corresponding to R v1 – X c1 ( E ‖ c ) transition is smaller than that of R v2 – X c2 ( E ⊥ c ) transition. Similar dependence has been found for the R – Y indirect transitions. The results of the investigation of the reflectance spectra in the energy range from 3 to 6 eV are shown. By using the Kramers–Kronig method, the optical functions were derived from the reflection spectra of nano-microribbons, and the polarization dependence of direct energy transitions at the point R in the Brillouin zone are determined. The alternation in splitting caused by polarization of the absorption edge related to indirect transitions due to polarization opens new prospects for the design and fabricating interesting optoelectronic devices based on α -MoO 3 bulk and nano-microribbons with characteristics dependent on the polarization of light waves.
BibTeX:
@article{Lupan2014,
author = {O Lupan and V Trofim and V Cretu and I Stamov and N N Syrbu and I Tiginyanu and Y K Mishra and R Adelung},
title = {Investigation of optical properties and electronic transitions in bulk and nano-microribbons of molybdenum trioxide},
journal = {Journal of Physics D: Applied Physics},
year = {2014},
volume = {47},
number = {8},
pages = {085302},
doi = {https://doi.org/10.1088/0022-3727/47/8/085302}
}
Versatile fabrication of complex shaped metal oxide nano-microstructures and their interconnected networks for multifunctional applications (invited review)
Y.K. Mishra, S. Kaps, A. Schuchardt, I. Paulowicz, X. Jin, D. Gedamu, S. Wille, O. Lupan and R. Adelung, KONA Powder Technology 2014, 31, 92-110.
Abstract:
Metal oxide nano-microstructures are applied in photocatalytic surfaces, sensors or biomedical engineering, proving the versatile utilization of nanotechnology. However, more complex or interconnected nano-microstructures are still seldomly met in practical applications, although they are of higher interest, due to enhanced structural, electronic and piezoelectric properties, as well as several complex biomedical effects, like antiviral characteristics. Here we attempt to present an overview of the novel, facile and cost-efficient flame transport synthesis (FTS) which allows controlled growth of different nano-microstructures and their interconnected networks in a scalable process. Various morphologies of nano-microstructures synthesized by FTS and its variants are demonstrated. These nano-microstructures have shown potential applications in different fields and the most relevant are reviewed here. Fabrication, growth mechanisms and properties of such large and highly porous three-dimensional (3D) interconnected networks of metal oxides (ZnO, SnO2, Fe2O3) nano-microstructures including carbon based aerographite material using FTS approaches are discussed along with their potential applications.
BibTeX:
@article{Mishra2014,
author = {Mishra, Y. K. and Kaps, S. and Schuchardt, A. and Paulowicz, I. and Jin, X. and Gedamu, D. and Wille, S. and Lupan, O. and Adelung, R.},
title = {Versatile fabrication of complex shaped metal oxide nano-microstructures and their interconnected networks for multifunctional applications (invited review)},
journal = {KONA Powder Technology},
year = {2014},
volume = {31},
pages = {92-110},
doi = {https://doi.org/10.14356/kona.2014015}
}
Trimorphism of N-(3-pyridyl)-benzamide
C. Nather, I. Jess, J. Bahrenburg, D. Bank and F. Temps, CrystEngComm 2014, 16, 5633-5641.
Abstract:
Three polymorphic modifications of N-(3-pyridyl)-benzamide (form I, monoclinic, space group P21/c, Z = 4, form II, monoclinic, space group P21, Z = 4 and form III, monoclinic, space group C2/c, Z = 8) were obtained and characterized by single crystal X-ray diffraction. In all forms significant differences in the torsion of the phenyl rings and the arrangement of the molecules in the crystal are observed. Quantum chemical calculations of the conformational barriers reveal only small differences and indicate that the conformation of form III is energetically favoured but this form does not represent the minimum energy conformation. In the crystal structures of all forms the molecules are connected via intermolecular N-HN (form I) and N-HO (form II and III) hydrogen bonds into chains. Solvent mediated conversion and DSC experiments indicate that form I represents the thermodynamically stable form between -20 [degree]C and its melting point. Solidification of the melt or sublimation leads directly to form I or to an amorphous material that transforms into form I on crystallization. Form II and form III cannot be obtained as phase-pure materials. Mixtures of form I and II with form II as the minor component can be obtained sometimes by crystallization under kinetic control. Upon heating these mixtures, form II transforms into form I in an endothermic reaction, which indicates that both modifications are enantiotropically related with form II being stable at lower temperatures. Thermomicroscopic investigations on selected single crystals of form III show a polymorphic transition presumably to form I because melting is observed at exactly the same temperature as measured for I.
BibTeX:
@article{Nather2014,
author = {Nather, Christian and Jess, Inke and Bahrenburg, Julia and Bank, Dennis and Temps, Friedrich},
title = {Trimorphism of N-(3-pyridyl)-benzamide},
journal = {CrystEngComm},
year = {2014},
volume = {16},
pages = {5633-5641},
doi = {https://doi.org/10.1039/C4CE00495G}
}
Ordered Monolayers of Free-Standing Porphyrins on Gold
F.L. Otte, S. Lemke, C. Schütt, N.R. Krekiehn, U. Jung, O.M. Magnussen and R. Herges, Journal of the American Chemical Society 2014, 136, 11248-11251.
Abstract:
The controlled attachment of chromophores to metal or semiconducting surfaces is a prerequisite for the construction of photonic devices and artificial surface-based light-harvesting systems. We present an approach to mount porphyrins in ordered monolayers on Au(111) by self-assembly and verify it, employing STM, absorption spectroscopy, and quantum chemical calculations. The usual adsorption geometry of planar chromophores, flat on the surface or densely packed edge-on, is prevented by mounting the porphyrins upright on a molecular platform. An ethynyl unit as spacer and pivot joint provides almost free azimuthal rotation of the unsubstituted porphin. However, rotation of the larger triphenylporphyrin unit is sterically restricted: because the diameter of the substituted porphyrin is larger than the distance to its next neighbors, the phenyl substituents of neigboring molecules interact by dispersion force, which leads to an alignment of the azimuthal rotators.
BibTeX:
@article{Otte2014,
author = {Otte, Franziska L. and Lemke, Sonja and Schütt, Christian and Krekiehn, Nicolai R. and Jung, Ulrich and Magnussen, Olaf M. and Herges, Rainer},
title = {Ordered Monolayers of Free-Standing Porphyrins on Gold},
journal = {Journal of the American Chemical Society},
year = {2014},
volume = {136},
pages = {11248-11251},
doi = {https://doi.org/10.1021/ja505563e}
}
Toxicity of Functional Nano-Micro Zinc Oxide Tetrapods: Impact of Cell Culture Conditions, Cellular Age and Material Properties
H. Papavlassopoulos, Y.K. Mishra, S. Kaps, I. Paulowicz, R. Abdelaziz, M. Elbahri, E. Maser, R. Adelung and C. Röhl, PLoS ONE 2014, 9, e84983.
Abstract:
With increasing production and applications of nanostructured zinc oxide, e.g., for biomedical and consumer products, the question of safety is getting more and more important. Different morphologies of zinc oxide structures have been synthesized and accordingly investigated. In this study, we have particularly focused on nano-micro ZnO tetrapods (ZnO-T), because their large scale fabrication has been made possible by a newly introduced flame transport synthesis approach which will probably lead to several new applications. Moreover, ZnO-T provide a completely different morphology then classical spherical ZnO nanoparticles. To get a better understanding of parameters that affect the interactions between ZnO-T and mammalian cells, and thus their biocompatibility, we have examined the impact of cell culture conditions as well as of material properties on cytotoxicity. Our results demonstrate that the cell density of fibroblasts in culture along with their age, i.e., the number of preceding cell divisions, strongly affect the cytotoxic potency of ZnO-T. Concerning the material properties, the toxic potency of ZnO-T is found to be significantly lower than that of spherical ZnO nanoparticles. Furthermore, the morphology of the ZnO-T influenced cellular toxicity in contrast to surface charges modified by UV illumination or O2 treatment and to the material age. Finally, we have observed that direct contact between tetrapods and cells increases their toxicity compared to transwell culture models which allow only an indirect effect via released zinc ions. The results reveal several parameters that can be of importance for the assessment of ZnO-T toxicity in cell cultures and for particle development.
BibTeX:
@article{Papavlassopoulos2014,
author = {Papavlassopoulos, , Heike AND Mishra, , Yogendra K. AND Kaps, , Sören AND Paulowicz, , Ingo AND Abdelaziz, , Ramzy AND Elbahri, , Mady AND Maser, , Edmund AND Adelung, , Rainer AND Röhl, , Claudia},
title = {Toxicity of Functional Nano-Micro Zinc Oxide Tetrapods: Impact of Cell Culture Conditions, Cellular Age and Material Properties},
journal = {PLoS ONE},
year = {2014},
volume = {9},
number = {1},
pages = {e84983},
doi = {https://doi.org/10.1371/journal.pone.0084983}
}
Wie klein ist ein Atom? Größenvorstellungen als Grundlage naturwissenschaftlicher Betrachtungen.
I. Parchmann, S. Schwarzer, P. Dierks, K. Könneker and J. Retzbach, Naturwissenschaft im Unterricht: Chemie 2014, 24, 32-33.
Abstract:
Wie groß ist die Erde, wie klein sind Atome? Realistische Vorstellungen von z. B. Den unvorstellbar kleinen Raummassen und Massen von Atomen sind eine bedeutsame Grundlage, um Messwerte und errechnete Ergebnisse hinsichtlich ihrer Sinnhaftigkeit einschätzen zu können. Es werden Beispiele für Aufgaben vorgestellt, die Anregungen bieten, im Chemieunterricht über Größendimensionen nachzudenken und Konsequenzen von "Größe" oder "Kleinheit" zu diskutieren.
BibTeX:
@article{Parchmann2014,
author = {Parchmann, I. and Schwarzer S. and Dierks, P. and Könneker, K. and Retzbach, J.},
title = {Wie klein ist ein Atom? Größenvorstellungen als Grundlage naturwissenschaftlicher Betrachtungen.},
journal = {Naturwissenschaft im Unterricht: Chemie},
year = {2014},
volume = {24},
pages = {32-33}
}
A density functional theory model of mechanically activated silyl ester hydrolysis
M.F. Pill, S.W. Schmidt, M.K. Beyer, H. Clausen-Schaumann and A. Kersch, The Journal of Chemical Physics 2014, 140, 044321.
Abstract:
To elucidate the mechanism of the mechanically activated dissociation of chemical bonds between carboxymethylated amylose (CMA) and silane functionalized silicon dioxide, we have investigated the dissociation kinetics of the bonds connecting CMA to silicon oxide surfaces with density functional calculations including the effects of force, solvent polarizability, and pH. We have determined the activation energies, the pre-exponential factors, and the reaction rate constants of candidate reactions. The weakest bond was found to be the silyl ester bond between the silicon and the alkoxy oxygen atom. Under acidic conditions, spontaneous proton addition occurs close to the silyl ester such that neutral reactions become insignificant. Upon proton addition at the most favored position, the activation energy for bond hydrolysis becomes 31 kJ mol−1, which agrees very well with experimental observation. Heterolytic bond scission in the protonated molecule has a much higher activation energy. The experimentally observed bi-exponential rupture kinetics can be explained by different side groups attached to the silicon atom of the silyl ester. The fact that different side groups lead to different dissociation kinetics provides an opportunity to deliberately modify and tune the kinetic parameters of mechanically activated bond dissociation of silyl esters.
BibTeX:
@article{Pill2014,
author = {Pill, Michael F. and Schmidt, Sebastian W. and Beyer, Martin K. and Clausen-Schaumann, Hauke and Kersch, Alfred},
title = {A density functional theory model of mechanically activated silyl ester hydrolysis},
journal = {The Journal of Chemical Physics},
year = {2014},
volume = {140},
pages = {044321},
doi = {https://doi.org/10.1063/1.4862827}
}
Ultrafast Z → E photoisomerisation of structurally modified furylfulgides
F. Renth, R. Siewertsen, F. Strübe, J. Mattay and F. Temps, Physical Chemistry Chemical Physics 2014, 16, 19556-19563.
Abstract:
Femtosecond broadband transient absorption spectroscopy has been used in a comparative study of the ultrafast photo-induced Z → E isomerisation reactions of four photochromic furylfulgides with selected structural motifs in n-hexane as solvent. The results show that all studied Z-fulgides exhibit fast and direct processes along barrierless excited-state pathways involving a conical intersection (CI) between the S1 and S0 electronic states. The excited-state lifetimes range from τ1 = 0.18 ps for the methyl derivative to τ1 = 0.32 ps for the benzofurylfulgide. The impulsive rise of the absorption by vibrationally hot Z- and E-isomers back in the electronic ground state following electronic deactivation and isomerisation indicates that the initially prepared wave packet persists even after passage of the CI. Furthermore, the results provide qualitative evidence for a quickly dephasing vibrational coherence in the electronic ground state. In contrast to the significant changes observed for the corresponding E- and C-isomers [Renth et al., Int. Rev. Phys. Chem., 2013, 32, 1–38], the excited-state dynamics of the Z-isomers is not affected by varied sterical hindrance from methyl and isopropyl substituents at the central hexatriene unit, or by intramolecular bridging, and remains unaltered upon extension of the π-electron system in a benzannulated furyl fulgide.
BibTeX:
@article{Renth2014,
author = {Renth, Falk and Siewertsen, Ron and Strübe, Frank and Mattay, Jochen and Temps, Friedrich},
title = {Ultrafast Z → E photoisomerisation of structurally modified furylfulgides},
journal = {Physical Chemistry Chemical Physics},
year = {2014},
volume = {16},
pages = {19556-19563},
doi = {https://doi.org/10.1039/c4cp01739k}
}
Detection of the G(-H)&x25cf; Radical in the Electronic Deactivation of the G-C Watson-Crick Base Pair
K. Röttger and F. Temps, in: 19th International Conference on Ultrafast Phenomena 2014 07.Mon.P1.20.
Abstract:
Transient absorption spectroscopy of the G-C base pair revealed the formation of the G(-H)&x25cf; radical with lifetime 3 ps in the electronic deactivation. This radical is the key intermediate in an electron-coupled proton transfer.
BibTeX:
@inproceedings{Roettger2014,
author = {Katharina Röttger and Friedrich Temps},
title = {Detection of the G(-H)&x25cf; Radical in the Electronic Deactivation of the G-C Watson-Crick Base Pair},
booktitle = {19th International Conference on Ultrafast Phenomena},
journal = {19th International Conference on Ultrafast Phenomena},
publisher = {Optical Society of America},
year = {2014},
pages = {07.Mon.P1.20},
doi = {https://doi.org/10.1364/UP.2014.07.Mon.P1.20}
}
Künstliches Blut – Synthese eines magnetisch und farblich schaltbaren Eisen-Komplexes.
J. Rudnik, H. Naggert, S. Schwarzer, F. Tuczek and I. Parchmann, CHEMKON 2014, 21, 85-88.
BibTeX:
@article{Rudnik2014,
author = {Rudnik, J. and Naggert, H. and Schwarzer, S. and Tuczek, F. and Parchmann, I.},
title = {Künstliches Blut – Synthese eines magnetisch und farblich schaltbaren Eisen-Komplexes.},
journal = {CHEMKON},
year = {2014},
volume = {21},
pages = {85-88},
doi = {https://doi.org/10.1002/ckon.201410222}
}
7-​Isopropylidene-​N2,​N3,​N5,​N6-​tetramethoxy-​N2,​N3,​N5,​N6-​tetramethylbicyclo[2.2.1]​hepta-​2,​5-​diene-​2,​3,​5,​6-​tetracarboxamide
B. Sahlmann, C. Näther and R. Herges, Acta Crystallographica Section E 2014, 70, o438.
Abstract:
Although the mol­ecular structure of the title compound, C22H32N4O8, displays a twofold symmetry of the mol­ecule including the meth­oxy and methyl substituents, no crystallographic twofold symmetry is observed in the X-ray structure analysis. The carbonyl O atoms alternately point to different sides of the plane defined by the carbonyl C atoms. Two meth­oxy groups are oriented inside the mol­ecules cavity. The H atoms of two methyl groups are disordered over two orientations and were refined using a split model.
BibTeX:
@article{Sahlmann2014,
author = {Sahlmann, Benjamin and Näther, Christian and Herges, Rainer},
title = {7-​Isopropylidene-​N2,​N3,​N5,​N6-​tetramethoxy-​N2,​N3,​N5,​N6-​tetramethylbicyclo[2.2.1]​hepta-​2,​5-​diene-​2,​3,​5,​6-​tetracarboxamide},
journal = {Acta Crystallographica Section E},
year = {2014},
volume = {70},
number = {4},
pages = {o438},
doi = {https://doi.org/10.1107/S1600536814004255}
}
Mechanically induced silyl ester cleavage under acidic conditions investigated by AFM-based single-molecule force spectroscopy in the force-ramp mode
S.W. Schmidt, M.F. Pill, A. Kersch, H. Clausen-Schaumann and M.K. Beyer, Faraday Discuss. 2014, 170, 357-367.
Abstract:
AFM-based dynamic single-molecule force spectroscopy was used to stretch carboxymethylated amylose (CMA) polymers, which have been covalently tethered between a silanized glass substrate and a silanized AFM tip via acid-catalyzed ester condensation at pH 2.0. Rupture forces were measured as a function of temperature and force loading rate in the force-ramp mode. The data exhibit significant statistical scattering, which is fitted with a maximum likelihood estimation (MLE) algorithm. Bond rupture is described with a Morse potential based Arrhenius kinetics model. The fit yields a bond dissociation energy De = 35 kJ mol-1 and an Arrhenius pre-factor A = 6.6[times]104 s-1. The bond dissociation energy is consistent with previous experiments under identical conditions, where the force-clamp mode was employed. However, the bi-exponential decay kinetics, which the force-clamp results unambiguously revealed, is not evident in the force-ramp data. While it is possible to fit the force-ramp data with a bi-exponential model, the fit parameters differ from the force-clamp experiments. Overall, single-molecule force spectroscopy in the force-ramp mode yields data whose information content is more limited than force-clamp data. It may, however, still be necessary and advantageous to perform force-ramp experiments. The number of successful events is often higher in the force-ramp mode, and competing reaction pathways may make force-clamp experiments impossible.
BibTeX:
@article{Schmidt2014,
author = {Schmidt, Sebastian W. and Pill, Michael Friedrich and Kersch, Alfred and Clausen-Schaumann, Hauke and Beyer, Martin K.},
title = {Mechanically induced silyl ester cleavage under acidic conditions investigated by AFM-based single-molecule force spectroscopy in the force-ramp mode},
journal = {Faraday Discuss.},
year = {2014},
volume = {170},
pages = {357-367},
doi = {https://doi.org/10.1039/C3FD00119A}
}
Spectroscopy of transmission resonances through a C 60 junction
N.L. Schneider, N. Néel, N.P. Andersen, J.T. Lü, M. Brandbyge, J. Kröger and R. Berndt, J. Phys.: Condens. Matter 2014, 27, 015001.
Abstract:
Electron transport through a single C60 molecule on Cu(1 1 1) has been investigated with a scanning tunnelling microscope in tunnelling and contact ranges. Single-C60 junctions have been fabricated by establishing a contact between the molecule and the tip, which is reflected by a down-shift in the lowest unoccupied molecular orbital resonance. These junctions are stable even at elevated bias voltages enabling conductance measurements at high voltages and nonlinear conductance spectroscopy in tunnelling and contact ranges. Spectroscopy and first principles transport calculations clarify the relation between molecular orbital resonances and the junction conductance. Due to the strong molecule–electrode coupling the simple picture of electron transport through individual orbitals does not hold.
BibTeX:
@article{Schneider2014,
author = {Schneider, N L and Néel, N and Andersen, N P and Lü, J T and Brandbyge, M and Kröger, J and Berndt, R},
title = {Spectroscopy of transmission resonances through a C 60 junction},
journal = {J. Phys.: Condens. Matter},
year = {2014},
volume = {27},
pages = {015001},
doi = {https://doi.org/10.1088/0953-8984/27/1/015001}
}
Photochemical dynamics of E-methylfurylfulgide-kinematic effects on photorelaxation dynamics of furylfulgides
J.B. Schönborn and B. Hartke, Phys. Chem. Chem. Phys. 2014, 16, 2483-2490.
Abstract:
With the present theoretical study of the photochemical switching of E-methylfurylfulgide we contribute an important step towards the understanding of the photochemical processes in furylfulgide-related molecules. We have carried out large-scale, full-dimensional direct semiempirical configuration-interaction surface-hopping dynamics of the photoinduced ring-closure reaction. Simulated static and dynamical UV/Vis-spectra show good agreement with experimental data of the same molecule. By a careful investigation of our dynamical data, we were able to identify marked differences to the dynamics of the previously studied E-isopropylfurylfulgide. With our simulations we can not only reproduce the experimentally observed quantum yield differences qualitatively but we can also pinpoint two reasons for them: kinematics and pre-orientation. With our analysis, we thus offer straightforward molecular explanations for the high sensitivity of the photodynamics towards seemingly minor changes in molecular constitution. Beyond the realm of furylfulgides, these insights provide additional guidance to the rational design of photochemically switchable molecules.
BibTeX:
@article{Schonborn2014,
author = {Schönborn, Jan Boyke and Hartke, Bernd},
title = {Photochemical dynamics of E-methylfurylfulgide-kinematic effects on photorelaxation dynamics of furylfulgides},
journal = {Phys. Chem. Chem. Phys.},
year = {2014},
volume = {16},
pages = {2483-2490},
doi = {https://doi.org/10.1039/C3CP53495B}
}
Mechanopolymerchemie - Molekulare Wirkung durch Kraft
M. Schulz-Senft, M. Lipfert and A. Staubitz, Chem. unserer Zeit 2014, 48, 200.
Abstract:
Although many methods can be employed to transfer energy to a chemical reaction, mechanical energy has not been widely used: It is difficult to apply mechanical forces high enough to lead to breaking bonds to small molecules. Work is the product of force and displacement but when the distances are small, very high forces are needed to obtain sufficient energy to break a bond. The situation is different in polymers, where the path length can be high. Here, bond cleavage, cycloreversions and isomerisations can be observed when mechanical energy is supplied, both in solution and solid systems. Mechanical energy can lead to different mechanistic pathways than those observed under thermal conditions or irradiation. Practical applications of the mechanochemistry of polymers are only just emerging and range from a better understanding of polymer decomposition under force to the development of strain sensors using mechanochromic polymers.
BibTeX:
@article{Schulz-Senft2014,
author = {Schulz-Senft, M. and Lipfert, M. and Staubitz, Anne},
title = {Mechanopolymerchemie - Molekulare Wirkung durch Kraft},
journal = {Chem. unserer Zeit},
year = {2014},
volume = {48},
pages = {200},
doi = {https://doi.org/10.1002/ciuz.201400640}
}
Fachdidaktische Begleitung eines Sonderforschungsbereichs – Strukturen einer gewinnbringenden Zusammenarbeit für Fach und Fachdidaktik.
S. Schwarzer, D. Ingwersen, R. Herges and I. Parchmann, Nachr. Chem. 2014, 62, in press.
BibTeX:
@article{Schwarzer2014a,
author = {Schwarzer, S. and Ingwersen, D. and Herges, R. and Parchmann, I.},
title = {Fachdidaktische Begleitung eines Sonderforschungsbereichs – Strukturen einer gewinnbringenden Zusammenarbeit für Fach und Fachdidaktik.},
journal = {Nachr. Chem.},
year = {2014},
volume = {62},
pages = {in press}
}
Schüler schalten chemisch.
S. Schwarzer, D. Ingwersen, R. Herges and I. Parchmann, Nachr. Chem. 2014, 62, 491-495.
Abstract:
Wenn chemische Grundlagenforschung und Fachdidaktik zusammenarbeiten, profitieren beide Seiten. Ein Beispiel ist der Sonderforschungsbereich “Funktion durch Schalten” an der Universität Kiel, dessen Ergebnisse und Arbeitsweisen nun in Chemieunterricht und Schülerlabor einfließen.
BibTeX:
@article{Schwarzer2014c,
author = {Schwarzer, Stefan and Ingwersen, Daniela and Herges, Rainer and Parchmann, Ilka.},
title = {Schüler schalten chemisch.},
journal = {Nachr. Chem.},
year = {2014},
volume = {62},
pages = {491-495},
doi = {https://doi.org/10.1002/nadc.201490145}
}
Wie Gecko & Co an die Decke gehen
S. Schwarzer, K. Kremer, L. Heepe, J. Arnold, S.N. Gorb and I. Parchmann, Praxis der Naturwissenschaften - Chemie in der Schule 2014, 2/63, .
BibTeX:
@article{Schwarzer2014,
author = {Schwarzer, S. and Kremer, K. and Heepe, L. and Arnold, J. and Gorb, S. N. and Parchmann, I.},
title = {Wie Gecko & Co an die Decke gehen},
journal = {Praxis der Naturwissenschaften - Chemie in der Schule},
year = {2014},
volume = {2/63}
}
Schaltbare Farbstoffe zur Reflexion von Schülervorstellungen am Phänomen Farbigkeit.
S. Schwarzer and I. Parchmann, Naturwissenschaften im Unterricht: Chemie 2014, 25, 44-47.
BibTeX:
@article{Schwarzer2014b,
author = {Schwarzer, S. and Parchmann, I.},
title = {Schaltbare Farbstoffe zur Reflexion von Schülervorstellungen am Phänomen Farbigkeit.},
journal = {Naturwissenschaften im Unterricht: Chemie},
year = {2014},
volume = {25},
pages = {44-47}
}
Tin Functionalized Azobenzenes as Nucleophiles in Stille Cross-Coupling Reactions
J. Strueben, P. Gates and A. Staubitz, J. Org. Chem. 2014, 79, 1719-1728.
Abstract:
The metalation of azobenzene by halogen–metal exchange typically leads to a reduction of the azo group to give hydrazine derivatives as major byproducts, instead of the desired metalated azobenzene species. In cross-coupling reactions, azobenzenes therefore usually serve as electrophiles, which greatly limits the scope of the reaction. To solve this problem, we have developed a mild and fast method to stannylate azobenzenes in high yields. This research shows that these stannylated azobenzenes can be used as nucleophilic components in Stille cross-coupling reactions with aryl bromides. The cross-coupling products were obtained in high yields ranging from 70 to 93%. With this reversal of the nucleophilic and electrophilic components, cross-coupling products are now accessible in which the aromatic rings coupled to the azobenzene bear functional groups that are sensitive to metalation.
BibTeX:
@article{Strueben2014,
author = {Strueben, J. and Gates, P.J. and Staubitz, Anne},
title = {Tin Functionalized Azobenzenes as Nucleophiles in Stille Cross-Coupling Reactions},
journal = {J. Org. Chem.},
year = {2014},
volume = {79},
pages = {1719-1728},
doi = {https://doi.org/10.1021/jo402598u}
}
Diazocines on Molecular Platforms
T. Tellkamp, J. Shen, Y. Okamoto and R. Herges, European Journal of Organic Chemistry 2014, 5456-5461.
Abstract:
New diazocines as photochromic switches for the surface functionalization via the “platform approach” were synthesized and characterized. Symmetric diazocines as well as asymmetric molecules based on an indane scaffold were obtained and their photochromic properties were investigated. In a final step, the diazocines were mounted on molecular platforms (triazatriangulenium ions).
BibTeX:
@article{Tellkamp2014,
author = {Tellkamp, Tobias and Shen, Jun and Okamoto, Yoshio and Herges, Rainer},
title = {Diazocines on Molecular Platforms},
journal = {European Journal of Organic Chemistry},
year = {2014},
pages = {5456-5461},
doi = {https://doi.org/10.1002/ejoc.201402541}
}
Switching of Bacterial Adhesion to a Glycosylated Surface by Reversible Reorientation of the Carbohydrate Ligand
T. Weber, V. Chandrasekaran, I. Stamer, M.B. Thygesen, A. Terfort and T.K. Lindhorst, Angewandte Chemie International Edition 2014, 53, 14583-14586.
Abstract:
The surface recognition in many biological systems is guided by the interaction of carbohydrate-specific proteins (lectins) with carbohydrate epitopes (ligands) located within the unordered glycoconjugate layer (glycocalyx) of cells. Thus, for recognition, the respective ligand has to reorient for a successful matching event. Herein, we present for the first time a model system, in which only the orientation of the ligand is altered in a controlled manner without changing the recognition quality of the ligand itself. The key for this orientational control is the embedding into an interfacial system and the use of a photoswitchable mechanical joint, such as azobenzene.
BibTeX:
@article{Weber2014a,
author = {Weber, Theresa and Chandrasekaran, Vijayanand and Stamer, Insa and Thygesen, Mikkel B. and Terfort, Andreas and Lindhorst, Thisbe K.},
title = {Switching of Bacterial Adhesion to a Glycosylated Surface by Reversible Reorientation of the Carbohydrate Ligand},
journal = {Angewandte Chemie International Edition},
year = {2014},
volume = {53},
pages = {14583-14586},
doi = {https://doi.org/10.1002/anie.201409808}
}
The whole is more than the sum of all its parts: collective effect of spider attachment organs
E. Wohlfart, J.O. Wolff, E. Arzt and S.N. Gorb, The Journal of Experimental Biology 2014, 217, 222-224.
Abstract:
Dynamic attachment is the key to moving safely and fast in a three-dimensional environment. Among lizards, hexapods and arachnids, several lineages have evolved hairy foot pads that can generate strong friction and adhesion on both smooth and rough surfaces. A strongly expressed directionality of attachment structures results in an anisotropy of frictional properties, which might be crucial for attachment control. In a natural situation, more than one leg is usually in contact with the substrate. In order to understand the collective effect of hairy foot pads in the hunting spider Cupiennius salei (Arachnida, Ctenidae), we performed vertical pulling experiments combined with stepwise disabling of the pads. We found the attachment force of the spider to be not simply the sum of single leg forces because with leg pair deactivation a much greater decrease in attachment forces was found than was predicted by just the loss of available adhesive pad area. This indicates that overall adhesion ability of the spider is strongly dependent on the antagonistic work of opposing legs, and the apparent contact area plays only a minor role. It is concluded that the coordinated action of the legs is crucial for adhesion control and for fast and easy detachment. The cumulative effect of anisotropic fibrillar adhesive structures could be potentially interesting for biomimetic applications, such as novel gripping devices.
BibTeX:
@article{Wohlfart2014,
author = {Wohlfart, Ellen and Wolff, Jonas O. and Arzt, Eduard and Gorb, Stanislav N.},
title = {The whole is more than the sum of all its parts: collective effect of spider attachment organs},
journal = {The Journal of Experimental Biology},
year = {2014},
volume = {217},
number = {2},
pages = {222-224},
doi = {https://doi.org/10.1242/jeb.093468}
}
Biomimetic Transferable Surface for a Real Time Control over Wettability and Photoerasable Writing with Water Drop Lens
A.U. Zillohu, R. Abdelaziz, S. Homaeigohar, I. Krasnov, M. Müller, T. Strunskus and M. Elbahri, Scientific Reports 2014, 4, 7407.
Abstract:
We demonstrate a transferable device that can turn wettability of surfaces to sticky or slippy, as per requirement. It is composed of polymeric yarn with a fibrous structure, which can be lifted and placed on any surface to render it the unique wettability properties. We introduce Polyvinylidenefluoride (PVDF) random fiber as biomimetic rose petal surface. When it is decorated with PVDF nanofibers yarns, the random mesh transform from rose petal sticky state into grass leaf slippy state. When it is placed on sticky, hydrophilic metal coin, it converts the surface of the coin to super hydrophobic. Adjustments in the yarn system, like interyarn spacing, can be done in real time to influence its wettability, which is a unique feature. Next, we load the polymer with a photochromic compound for chemical restructuring. It affects the sliding angle of water drop and makes the fibers optically active. We also demonstrate a “water droplets lens” concept that enables erasable writing on photochromic rose petal sticky fibrous surface. The droplet on a highly hydrophobic surface acts as a ball lens to concentrate light onto a hot spot; thereby we demonstrate UV light writing with water lenses and visible light erasing.
BibTeX:
@article{Zillohu2014a,
author = {Zillohu, Ahnaf Usman and Abdelaziz, Ramzy and Homaeigohar, Shahin and Krasnov, Igor and Müller, Martin and Strunskus, Thomas and Elbahri, Mady},
title = {Biomimetic Transferable Surface for a Real Time Control over Wettability and Photoerasable Writing with Water Drop Lens},
journal = {Scientific Reports},
year = {2014},
volume = {4},
pages = {7407},
doi = {https://doi.org/10.1038/srep07407}
}
Thermo-Plasmonics for Localized Graphitization and Welding of Polymeric Nanofibers
A.U. Zillohu, N. Alissawi, R. Abdelaziz and M. Elbahri, Materials 2014, 7, 323-332.
Abstract:
There is a growing interest in modulating the temperature under the illumination of light. As a heat source, metal nanoparticles (NPs) have played an important role to pave the way for a new branch of plasmonics, i.e., thermo-plasmonics. While thermo-plasmonics have been well established in photo-thermal therapy, it has received comparatively less attention in materials science and chemistry. Here, we demonstrate the first proof of concept experiment of local chemistry and graphitization of metalized polymeric nanofibers through thermo-plasmonic effect. In particular, by tuning the plasmonic absorption of the nanohybrid through a change in the thickness of the deposited silver film on the fibers, the thermo-plasmonic effect can be adjusted in such a way that high enough temperature is generated enabling local welding and graphitization of the polymeric nanofibers.
BibTeX:
@article{Zillohu2014,
author = {Zillohu, Ahnaf Usman and Alissawi, Nisreen and Abdelaziz, Ramzy and Elbahri, Mady},
title = {Thermo-Plasmonics for Localized Graphitization and Welding of Polymeric Nanofibers},
journal = {Materials},
year = {2014},
volume = {7},
number = {1},
pages = {323-332},
doi = {https://doi.org/10.3390/ma7010323}
}
Green chemistry and nanofabrication in a levitated Leidenfrost drop
R. Abdelaziz, D. Disci-Zayed, M. Keshavarz Hedayati, J.-H. Pöhls, A. Usman Zillohu, B. Erkartal, V.S.K. Chakravadhanula, V. Duppel, L. Kienle and M. Elbahri, Nature Communications 2013, 4, 2400.
Abstract:
Green nanotechnology focuses on the development of new and sustainable methods of creating nanoparticles, their localized assembly and integration into useful systems and devices in a cost-effective, simple and eco-friendly manner. Here we present our experimental findings on the use of the Leidenfrost drop as an overheated and charged green chemical reactor. Employing a droplet of aqueous solution on hot substrates, this method is capable of fabricating nanoparticles, creating nanoscale coatings on complex objects and designing porous metal in suspension and foam form, all in a levitated Leidenfrost drop. As examples of the potential applications of the Leidenfrost drop, fabrication of nanoporous black gold as a plasmonic wideband superabsorber, and synthesis of superhydrophilic and thermal resistive metal–polymer hybrid foams are demonstrated. We believe that the presented nanofabrication method may be a promising strategy towards the sustainable production of functional nanomaterials.
BibTeX:
@article{Abdelaziz2013,
author = {Abdelaziz, Ramzy and Disci-Zayed, Duygu and Keshavarz Hedayati, Mehdi and Pöhls, Jan-Hendrik and Usman Zillohu, Ahnaf and Erkartal, Burak and Chakravadhanula, Venkata Sai Kiran and Duppel, Viola and Kienle, Lorenz and Elbahri, Mady},
title = {Green chemistry and nanofabrication in a levitated Leidenfrost drop},
journal = {Nature Communications},
year = {2013},
volume = {4},
pages = {2400},
doi = {https://doi.org/10.1038/ncomms3400}
}
Photochemical properties of multi-azobenzene compounds
J. Bahrenburg, C.M. Sievers, J.B. Schonborn, B. Hartke, F. Renth, F. Temps, C. Nather and F.D. Sönnichsen, Photochem. Photobiol. Sci. 2013, 12, 511-518.
Abstract:
A systematic study is reported of the photochemical properties of the multi-azobenzene compounds bis[4-(phenylazo)phenyl]amine (BPAPA) and tris[4-(phenylazo)phenyl]amine (TPAPA) compared to the parent molecule 4-aminoazobenzene (AAB). The bis- and tris-azobenzenes were synthesised by a variant of the Ullmann reaction and exist in their stable all-E forms at room temperature. Striking changes in the spectral positions and intensities of their first [small pi][small pi]* absorption bands compared to AAB reveal strong electronic coupling between the AB units. The nature of the excited states was explored by quantum chemical calculations at the approximate coupled-cluster (CC2) level. Upon UV/VIS irradiation, the molecules isomerise to the Z-isomer (AAB), ZE- and ZZ-isomers (BPAPA), and ZEE-, ZZE- and ZZZ-isomers (TPAPA), respectively. The photoswitching behaviours were investigated by UV/VIS and NMR spectroscopies. All individual isomers were detected by one-dimensional (1D) 1H NMR spectroscopy (BPAPA) and two-dimensional (2D) HSQC NMR spectroscopy (TPAPA). A kinetic analysis provided the isomer-specific thermal lifetimes. The variance of the thermal lifetimes demonstrates a dependence of the Z-E isomerisation on the chromophore size and number of AB units.
BibTeX:
@article{Bahrenburg2013,
author = {Bahrenburg, Julia and Sievers, Claudia M. and Schonborn, Jan Boyke and Hartke, Bernd and Renth, Falk and Temps, Friedrich and Nather, Christian and Sönnichsen, Frank D.},
title = {Photochemical properties of multi-azobenzene compounds},
journal = {Photochem. Photobiol. Sci.},
year = {2013},
volume = {12},
pages = {511-518},
doi = {https://doi.org/10.1039/C2PP25291K}
}
Wie dünn ist eine Seifenblase? Ein experimenteller Zugang zu Mikro- und Nanoschichten
M. Baum and S. Schwarzer, CHEMKON 2013, 20, 25-28.
BibTeX:
@article{Baum2013,
author = {Baum, Michael and Schwarzer, Stefan},
title = {Wie dünn ist eine Seifenblase? Ein experimenteller Zugang zu Mikro- und Nanoschichten},
journal = {CHEMKON},
year = {2013},
volume = {20},
number = {1},
pages = {25-28},
doi = {https://doi.org/10.1002/ckon.201210193}
}
Atomic-scale inversion of spin polarization at an organic-antiferromagnetic interface
N.M. Caffrey, P. Ferriani, S. Marocchi and S. Heinze, Phys. Rev. B 2013, 88, 155403.
Abstract:
Using first-principles calculations, we show that the magnetic properties of a two-dimensional antiferromagnetic transition-metal surface are modified on the atomic scale by the adsorption of small organic molecules. We consider benzene (C6H6), cyclooctatetraene (C8H8), and a small transition-metal–benzene complex (BzV) adsorbed on a single atomic layer of Mn deposited on the W(110) surface—a surface which exhibits a nearly antiferromagnetic alignment of the magnetic moments in adjacent Mn rows. Due to the spin dependent hybridization of the molecular pz orbitals with the d states of the Mn monolayer, there is a significant reduction of the magnetic moments in the Mn film. Furthermore, the spin polarization at this organic-antiferromagnetic interface is found to be modulated on the atomic scale, both enhanced and inverted, as a result of the molecular adsorption. We show that this effect can be resolved by spin-polarized scanning tunneling microscopy (SP-STM). Our simulated SP-STM images display a spatially dependent spin resolved vacuum charge density above an adsorbed molecule—i.e., different regions above the molecule sustain different signs of spin polarization. While states with s and p symmetry dominate the vacuum charge density in the vicinity of the Fermi energy for the clean magnetic surface, we demonstrate that after a molecule is adsorbed those d states, which are normally suppressed due to their symmetry, can play a crucial role in the vacuum due to their interaction with the molecular orbitals. We also model the effect of small deviations from perfect antiferromagnetic ordering, induced by the slight canting of magnetic moments due to the spin spiral ground state of Mn/W(110).
BibTeX:
@article{Caffrey2013,
author = {Caffrey, Nuala M. and Ferriani, Paolo and Marocchi, Simone and Heinze, Stefan},
title = {Atomic-scale inversion of spin polarization at an organic-antiferromagnetic interface},
journal = {Phys. Rev. B},
year = {2013},
volume = {88},
pages = {155403},
doi = {https://doi.org/10.1103/PhysRevB.88.155403}
}
QM/MM surface-hopping dynamics of a bridged azobenzene derivative
N.O. Carstensen, Phys. Chem. Chem. Phys. 2013, 15, 15017.
Abstract:
Ethylene-bridged azobenzene (diazocine) has been shown to have superior photochemical properties. So far, however, experimental and theoretical quantum yields did not match, not even qualitatively. Here, a large-scale QM/MM surface-hopping study of this molecule is presented. For both photo-isomerization directions, surprisingly prominent solvent effects are found and analyzed by detailed comparisons against gas phase dynamics and experimental data. By taking explicit n-hexane solvent into account, the quantum yields change markedly and approach the experimental values, where the same solvent was used.
BibTeX:
@article{Carstensen2013,
author = {Carstensen, Niss Ole},
title = {QM/MM surface-hopping dynamics of a bridged azobenzene derivative},
journal = {Phys. Chem. Chem. Phys.},
year = {2013},
volume = {15},
pages = {15017},
doi = {https://doi.org/10.1039/C3CP50606A}
}
Synthesis and testing of the first azobenzene mannobioside as photoswitchable ligand for the bacterial lectin FimH
V. Chandrasekaran, K. Kolbe, F. Beiroth and T.K. Lindhorst, Beilstein Journal of Organic Chemistry 2013, 9, 223-233.
Abstract:
In order to allow spatial and temporal control of carbohydrate-specific bacterial adhesion, it has become our goal to synthesise azobenzene mannosides as photoswitchable inhibitors of type 1 fimbriae-mediated adhesion of E. coli. An azobenzene mannobioside 2 was prepared and its photochromic properties were investigated. The E→Z isomerisation was found to be highly effective, yielding a long-lived (Z)-isomer. Both isomers, E and Z, show excellent water solubility and were tested as inhibitors of mannoside-specific bacterial adhesion in solution. Their inhibitory potency was found to be equal and almost two orders of magnitude higher than that of the standard inhibitor methyl mannoside. These findings could be rationalised on the basis of computer-aided docking studies. The properties of the new azobenzene mannobioside have qualified this glycoside to be eventually employed on solid support, in order to fabricate photoswitchable adhesive surfaces.
BibTeX:
@article{Chandrasekaran2013,
author = {Vijayanand Chandrasekaran and Katharina Kolbe and Femke Beiroth and Thisbe K. Lindhorst},
title = {Synthesis and testing of the first azobenzene mannobioside as photoswitchable ligand for the bacterial lectin FimH},
journal = {Beilstein Journal of Organic Chemistry},
year = {2013},
volume = {9},
pages = {223-233},
doi = {https://doi.org/10.3762/bjoc.9.26}
}
Rapid Fabrication Technique for Interpenetrated ZnO Nanotetrapod Networks for Fast UV Sensors
D. Gedamu, I. Paulowicz, S. Kaps, O. Lupan, S. Wille, G. Haidarschin, Y.K. Mishra and R. Adelung, Advanced Materials 2013, 26, 1541-1550.
Abstract:
Two flame-based synthesis methods- burner flame transport synthesis (B-FTS) and crucible flame transport synthesis (C-FTS) for fabricating ZnO nanostructure based UV photodetectors are presented. The B-FTS allows rapid growth of ZnO nanotetrapods and in situ bridging them into electrical contacts. The photodetector made from interconnected ZnO nanotetrapod networks exhibit fast response/recovery times and high current ratio under UV illuminations.
BibTeX:
@article{Gedamu2013,
author = {Gedamu, Dawit and Paulowicz, Ingo and Kaps, Sören and Lupan, Oleg and Wille, Sebastian and Haidarschin, Galina and Mishra, Yogendra Kumar and Adelung, Rainer},
title = {Rapid Fabrication Technique for Interpenetrated ZnO Nanotetrapod Networks for Fast UV Sensors},
journal = {Advanced Materials},
year = {2013},
volume = {26},
pages = {1541-1550},
doi = {https://doi.org/10.1002/adma.201304363}
}
Spin-Crossover Complex on Au(111): Structural and Electronic Differences Between Mono- and Multilayers
T.G. Gopakumar, M. Bernien, H. Naggert, F. Matino, C.F. Hermanns, A. Bannwarth, S. Mühlenberend, A. Krüger, D. Krüger, F. Nickel, W. Walter, R. Berndt, W. Kuch and F. Tuczek, Chemistry – A European Journal 2013, 19, 15702-15709.
Abstract:
Submono-, mono- and multilayers of the Fe(II) spin-crossover (SCO) complex [Fe(bpz)2(phen)] (bpz=dihydrobis(pyrazolyl)borate, phen=1,10-phenanthroline) have beenprepared by vacuum deposition on Au(111) substrates and investigated with near edge X-ray absorption fine structure (NEXAFS) spectroscopy and scanning tunneling microscopy (STM). As evidenced by NEXAFS, molecules of the second layer exhibit a thermal spin crossover transition, although with a more gradual characteristics than in the bulk. For mono- and submonolayers of [Fe(bpz)2(phen)] deposited on Au(111) substrates at room temperature both NEXAFS and STM indicate a dissociation of [Fe(bpz)2(phen)] on Au(111) into four-coordinate complexes, [Fe(bpz)2], and phen molecules. Keeping the gold substrate at elevated temperatures ordered monolayers of intact molecules of [Fe(bpz)2(phen)] are formed which can be spin-switched by electron-induced excited spin-state trapping (ELIESST).
BibTeX:
@article{Gopakumar2013a,
author = {Gopakumar, Thiruvancheril G. and Bernien, Matthias and Naggert, Holger and Matino, Francesca and Hermanns, Christian F. and Bannwarth, Alexander and Mühlenberend, Svenja and Krüger, Alex and Krüger, Dennis and Nickel, Fabian and Walter, Waldemar and Berndt, Richard and Kuch, Wolfgang and Tuczek, Felix},
title = {Spin-Crossover Complex on Au(111): Structural and Electronic Differences Between Mono- and Multilayers},
journal = {Chemistry – A European Journal},
year = {2013},
volume = {19},
number = {46},
pages = {15702-15709},
doi = {https://doi.org/10.1002/chem.201302241}
}
Broken Symmetry of an Adsorbed Molecular Switch Determined by Scanning Tunneling Spectroscopy
T.G. Gopakumar, T. Davran-Candan, J. Bahrenburg, R.J. Maurer, F. Temps, K. Reuter and R. Berndt, Angewandte Chemie International Edition 2013, 52, 11007-11010.
Abstract:
An asymmetric turn: Scanning tunneling spectroscopy has been used to analyze the structure of tris[4-(phenylazo)phenyl)]amine on a Au(111) surface. A degenerate marker state serves as a sensitive probe for the structure of the adsorbed molecules.
BibTeX:
@article{Gopakumar2013,
author = {Gopakumar, Thiruvancheril G. and Davran-Candan, Tugba and Bahrenburg, Julia and Maurer, Reinhard J. and Temps, Friedrich and Reuter, Karsten and Berndt, Richard},
title = {Broken Symmetry of an Adsorbed Molecular Switch Determined by Scanning Tunneling Spectroscopy},
journal = {Angewandte Chemie International Edition},
year = {2013},
volume = {52},
pages = {11007-11010},
doi = {https://doi.org/10.1002/anie.201305027}
}
A 'dual click' strategy for the fabrication of bioselective, glycosylated self-assembled monolayers as glycocalyx models
C. Grabosch, M. Kind, Y. Gies, F. Schweighofer, A. Terfort and T.K. Lindhorst, Org. Biomol. Chem. 2013, 11, 4006-4015.
Abstract:
Solid surfaces decorated with specific saccharide patterns can serve as a model for the chemically and structurally highly complex glycocalyx of eukaryotic cells. Here we present an approach based on self-assembled monolayers on gold, which are built up in a three-step manner to provide a solid basis, a biorepulsive oligoethylene glycol part, and a specific carbohydrate terminus in a modular way. Of the different reaction sequences, the one with two consecutive 'click reactions' (the copper(i)-catalysed 1,3-dipolar cycloaddition of alkynes with azides and the thiourea-bridging of isothiocyanates with amines) directly 'on SAM' results in the densest layers, as demonstrated by infrared absorption reflection spectroscopy and ellipsometry. As a 'real life' test, the surfaces obtained this way were used for bacterial adhesion experiments. Here the biorepulsivity of the middle part of the SAMs as well as specific binding to the carbohydrate termini could be clearly demonstrated.
BibTeX:
@article{Grabosch2013,
author = {Grabosch, Carsten and Kind, Martin and Gies, Yasmin and Schweighofer, Felix and Terfort, Andreas and Lindhorst, Thisbe K.},
title = {A 'dual click' strategy for the fabrication of bioselective, glycosylated self-assembled monolayers as glycocalyx models},
journal = {Org. Biomol. Chem.},
year = {2013},
volume = {11},
pages = {4006-4015},
doi = {https://doi.org/10.1039/C3OB40386F}
}
Switching and charging of a ruthenium dye on Ag(111)
N. Hauptmann, C. Hamann, H. Tang and R. Berndt, Phys. Chem. Chem. Phys. 2013, 15, 10326-10330.
Abstract:
The ruthenium dye N3, cis-bis(isothiocyanato)bis(2,2[prime or minute]-bipyridyl-4,4[prime or minute]-dicarboxylato)-ruthenium(ii), deposited on Ag(111) by ultra-high vacuum electrospray ionization is investigated using low-temperature scanning tunneling microscopy. Scanning tunneling spectroscopy of single molecules reveals vibronic excitations that are related to the lowest unoccupied molecular orbital (LUMO). Switching of N3 may be induced and modifies the energy of the negative ion resonance as well as the vibrational progression. Moreover, charging of the molecule is induced at reverse bias. These data suggest a surprisingly weak electronic coupling of N3 to the Ag substrate. A double-barrier model reproduces the essential spectral features.
BibTeX:
@article{Hauptmann2013a,
author = {Hauptmann, Nadine and Hamann, Christian and Tang, Hao and Berndt, Richard},
title = {Switching and charging of a ruthenium dye on Ag(111)},
journal = {Phys. Chem. Chem. Phys.},
year = {2013},
volume = {15},
pages = {10326-10330},
doi = {https://doi.org/10.1039/C3CP51023A}
}
Soft-Landing Electrospray Deposition of the Ruthenium Dye N3 on Au(111)
N. Hauptmann, C. Hamann, H. Tang and R. Berndt, The Journal of Physical Chemistry C 2013, 117, 9734-9738.
Abstract:
Ruthenium dyes (N3) are deposited by in situ ultrahigh vacuum (UHV) electrospray ionization on a Au(111) surface and investigated using scanning tunneling microscopy and spectroscopy. The molecules exhibit some fragmentation at deposition energies around 7 eV, while deposition of intact molecules is feasible with energies of 2.5 eV. A variety of adsorption geometries is found that are analyzed using spectroscopy of vibronic excitations and DFT calculations.
BibTeX:
@article{Hauptmann2013b,
author = {Hauptmann, Nadine and Hamann, Christian and Tang, Hao and Berndt, Richard},
title = {Soft-Landing Electrospray Deposition of the Ruthenium Dye N3 on Au(111)},
journal = {The Journal of Physical Chemistry C},
year = {2013},
volume = {117},
pages = {9734-9738},
doi = {https://doi.org/10.1021/jp311420d}
}
Surface Control of Alkyl Chain Conformations and 2D Chiral Amplification
N. Hauptmann, K. Scheil, T.G. Gopakumar, F.L. Otte, C. Schütt, R. Herges and R. Berndt, Journal of the American Chemical Society 2013, 135, 8814-8817.
Abstract:
Trioctyl-functionalized triazatriangulenium (trioctyl-TATA) deposited on Au(111) and Ag(111) surfaces by electrospray ionization was investigated using low-temperature scanning tunneling microscopy. The molecule surprisingly adsorbs with gauche rather than anti conformations of the octyl groups. We observed chiral amplification in the islands. Only one of the eight possible configurations of the octyl groups was found in homochiral hexagonal networks. Quantum-chemical calculations confirmed and explained the preference for the gauche conformations of adsorbed trioctyl-TATA.
BibTeX:
@article{Hauptmann2013,
author = {Hauptmann, Nadine and Scheil, Katharina and Gopakumar, Thiruvancheril G. and Otte, Franziska L. and Schütt, Christian and Herges, Rainer and Berndt, Richard},
title = {Surface Control of Alkyl Chain Conformations and 2D Chiral Amplification},
journal = {Journal of the American Chemical Society},
year = {2013},
volume = {135},
pages = {8814-8817},
doi = {https://doi.org/10.1021/ja4036187}
}
Adhesion failure at 180,000 frames per second: Direct observation of detachment Process of a Mushroom-Shaped Adhesive
L. Heepe, A.E. Kovalev, A.E. Filippov and S.N. Gorb, Phys. Rev. Lett. 2013, 104301.
Abstract:
Nature has successfully evolved the mushroom-shaped contact geometry in many organisms in order to solve the attachment problem. We studied the detachment process of individual bio-inspired artificial mushroom-shaped adhesive microstructure (MSAMS) resolving the failure dynamics at high spatiotemporal resolution. The experimental data provide strong evidence for a homogeneous stress distribution in MSAMS which was recently proposed. Our results allow us to explain the advantage of such contact geometry and provide a suggestion for the widely observed mushroom-shaped contact geometry.
BibTeX:
@article{Heepe2013,
author = {Lars Heepe and Alexander E. Kovalev and Alexander E. Filippov and Stanislav N. Gorb},
title = {Adhesion failure at 180,000 frames per second: Direct observation of detachment Process of a Mushroom-Shaped Adhesive},
journal = {Phys. Rev. Lett.},
year = {2013},
pages = {104301},
doi = {https://doi.org/10.1103/PhysRevLett.111.104301}
}
Biofunctionalized nanofibrous membranes mimicking carnivorous plants
S. Homaeigohar, D. 2. Disci-Zayed, T. Dai and M. Elbahri, Bioinspired, Biomimetic and Nanobiomaterials 2013, 2, 186-193.
Abstract:
A novel biofunctionalized nanofibrous membrane is developed through immobilization of protein ligands on the surface of nanofibers. The biofunctionalization not only enhances the membrane’s structural properties including mechanical and thermal ones but also makes the membrane capable to separate nanoparticles and biomolecules much smaller than the pore size from water efficiently. Upon contact with water, the conformational change of the protein immobilized leads to its swelling, thereby an enlarged functional surface area and a higher steric hindrance capturing the filtrates. In case of filtration of a plasmonic nanoparticle containing suspension, decoration of the membrane with the plasmonic nanoparticles forms a smart bionanocomposite biosensor for detection of protein denaturation.
BibTeX:
@article{Homaeigohar2013,
author = {Homaeigohar, Shahin and Disci-Zayed, Duygu 2 and Dai, Tianhe and Elbahri, Mady},
title = {Biofunctionalized nanofibrous membranes mimicking carnivorous plants},
journal = {Bioinspired, Biomimetic and Nanobiomaterials},
year = {2013},
volume = {2},
pages = {186-193},
doi = {https://doi.org/10.1680/bbn.13.00006}
}
Grafting of Functionalized [Fe(III)(salten)] Complexes to Au(111) Surfaces via Thiolate Groups: Surface Spectroscopic Characterization and Comparison of Different Linker Designs
H. Jacob, K. Kathirvel, F. Petersen, T. Strunskus, A. Bannwarth, S. Meyer and F. Tuczek, Langmuir 2013, 29, 8534-8543.
Abstract:
Functionalization of surfaces with spin crossover complexes is an intensively studied topic. Starting from dinuclear iron(III)-salten complexes [Fe(salten)(pyS)]2(BPh4)2 and [Fe(thiotolylsalten)(NCS)]2 with disulfide-containing bridging ligands, corresponding mononuclear complexes [Fe(salten)(pyS)]+ and [Fe(thiotolylsalten)(NCS)] are covalently attached to Au(111) surfaces (pySH, pyridinethiol; salten, bis(3-salicylidene-aminopropyl)amine). The adsorbed monolayers are investigated by infrared reflection absorption spectroscopy (IRRAS) in combination with X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). Comparison of the surface vibrational spectra with bulk data allows us to draw conclusions with respect to the geometry of the adsorbed complexes. An anomaly is observed in the spectra of the surface-adsorbed monolayer of [Fe(salten)(pyS)]+, which suggests that the salten ligand is partially decoordinated from the Fe(III) center and one of its phenolate arms binds to the Au(111) surface. For complex [Fe(thiotolylsalten)(NCS)] that is bound to the Au(111) surface via a thiolate-functionalized salten ligand, this anomaly is not observed, which indicates that the coordination sphere of the complex in the bulk is retained on the surface. The implications of these results with respect to the preparation of surface-adsorbed monolayers of functional transition-metal complexes are discussed.
BibTeX:
@article{Jacob2013,
author = {Jacob, Hanne and Kathirvel, Ketheeswari and Petersen, Finn and Strunskus, Thomas and Bannwarth, Alexander and Meyer, Sven and Tuczek, Felix},
title = {Grafting of Functionalized [Fe(III)(salten)] Complexes to Au(111) Surfaces via Thiolate Groups: Surface Spectroscopic Characterization and Comparison of Different Linker Designs},
journal = {Langmuir},
year = {2013},
volume = {29},
pages = {8534-8543},
doi = {https://doi.org/10.1021/la400663y}
}
A Novel Concept for Self-Reporting Materials: Stress Sensitive Photoluminescence in ZnO Tetrapod Filled Elastomers
X. Jin, M. Götz, S. Wille, Y.K. Mishra, R. Adelung and C. Zollfrank, Advanced Materials 2013, 25, 1342-1347.
Abstract:
The stress-induced photo-luminescence response of tetrapodal shaped ZnO filler embedded in a silicone elastomer is used to demonstrate a novel concept for self-reporting materials. Applied tensile stress can be followed in composites with low and high filler fractions by measuring the photoluminescence response of the T-ZnO. The deformation of the interlocked ZnO network appears to be essential for the self-reporting mechanism.
BibTeX:
@article{Jin2013,
author = {Jin, Xin and Götz, Michael and Wille, Sebastian and Mishra, Yogendra Kumar and Adelung, Rainer and Zollfrank, Cordt},
title = {A Novel Concept for Self-Reporting Materials: Stress Sensitive Photoluminescence in ZnO Tetrapod Filled Elastomers},
journal = {Advanced Materials},
year = {2013},
volume = {25},
number = {9},
pages = {1342-1347},
doi = {https://doi.org/10.1002/adma.201203849}
}
Studies of the molecular switching of azobenzene-functionalized platform adlayers on Au(111) by chronoamperometry
U. Jung, J. Kubitschke, R. Herges and O. Magnussen, Electrochimica Acta 2013, 112, 869-880.
Abstract:
Abstract Photochronoamperometry is introduced as a new approach to study isomerization reactions in photoswitchable molecular adsorbate layers on metal electrodes. Using highly ordered self-assembled monolayers of molecular platforms with freestanding vertical azobenzene functionalities on single-crystalline Au(111) as an example, the photoinduced current response was measured as a function of potential and irradiation intensity and compared to complementary cyclic voltammetry studies. The observed behavior is discussed within a kinetical model that qualitatively describes the experimental findings. In order to describe the intensity dependence, the isomerization reactions, in particular, the thermal relaxation, have to occur distinctively faster than the electrochemical processes, which is in good agreement with previous results for these photoswitchable adlayers.
BibTeX:
@article{Jung2013,
author = {Ulrich Jung and Jens Kubitschke and Rainer Herges and Olaf Magnussen},
title = {Studies of the molecular switching of azobenzene-functionalized platform adlayers on Au(111) by chronoamperometry},
journal = {Electrochimica Acta},
year = {2013},
volume = {112},
pages = {869-880},
doi = {https://doi.org/10.1016/j.electacta.2013.06.123}
}
Surface-Supported Supramolecular Pentamers
S. Karan, Y. Wang, R. Robles, N. Lorente and R. Berndt, Journal of the American Chemical Society 2013, 135, 14004-14007.
Abstract:
Chiral pentamers of all-trans-retinoic acid molecules have been prepared on Au(111) surfaces and on a molecular monolayer. Over a range of coverages, pentamers are the building blocks of larger arrays that become increasingly enantiopure. The stability of pentamers is analyzed from experiments on an isomer and a more reactive substrate as well as from density functional theory. The linear shape of the molecule and suitable densities are crucial for the formation of pentamers, driven by cyclic hydrogen bonding between carboxylic acid moieties.
BibTeX:
@article{Karan2013,
author = {Karan, Sujoy and Wang, Yongfeng and Robles, Roberto and Lorente, Nicolás and Berndt, Richard},
title = {Surface-Supported Supramolecular Pentamers},
journal = {Journal of the American Chemical Society},
year = {2013},
volume = {135},
pages = {14004-14007},
doi = {https://doi.org/10.1021/ja405456k}
}
Underwater Adhesion of Mushroom-shaped Adhesive Microstructure: An Air-entrapment Effect
E. Kizilkan, L. Heepe and S. Gorb, in: Biological and Biomimetic Adhesives: Challenges and Opportunities. 2013, 65-71.
Abstract:
In this work, we revisited the underwater adhesion of mushroom-shaped adhesive microstructure (MSAMS) which has come a long way from the inspiration of attachment devices evolved in beetles to a large-scale industrial production. It was shown that MSAMS has an about twice higher pull-off force compared to smooth control made from the same material measured in air. Enhanced adhesion was found to be a combination of intermolecular van der Waals forces and particular crack-trapping geometry. Recently, it was shown that underwater adhesion of MSAMS was even higher than that in air (M. Varenberg, and S. N. Gorb, J. R. Soc. Interface 5, 383, 2008). It was a surprising result, since van der Waals interactions should theoretically be strongly reduced, when the surfaces are submerged in water. It was hypothesized that each individual MSAMS acts as a passive suction device. The present study aims at an experimental investigation of an alternative hypothesis, namely the effect of air-entrapment. For this purpose, we compared pull-off forces of MSAMS, measured under water with a layer of entrapped air with those completely wetted by water. In the presence of an air layer pull-off forces were distinctly higher compared to measurements performed in air. When MSAMS was completely wetted by water, lower pull-off forces compared to those measured in air were obtained. These data suggest that air retaining capabilities of MSAMS, when submerged in water, may also explain their enhanced underwater adhesion.
BibTeX:
@incollection{Kizilkan2013,
author = {Kizilkan, E. and Heepe, L. and Gorb, S.N.},
title = {Underwater Adhesion of Mushroom-shaped Adhesive Microstructure: An Air-entrapment Effect},
booktitle = {Biological and Biomimetic Adhesives: Challenges and Opportunities},
year = {2013},
pages = {65-71},
doi = {https://doi.org/10.1039/9781849737135-00065}
}
Global optimization of parameters in the reactive force field ReaxFF for SiOH
H.R. Larsson, A.C.T. van Duin and B. Hartke, Journal of Computational Chemistry 2013, 34, 2178-2189.
Abstract:
We have used unbiased global optimization to fit a reactive force field to a given set of reference data. Specifically, we have employed genetic algorithms (GA) to fit ReaxFF to SiOH data, using an in-house GA code that is parallelized across reference data items via the message-passing interface (MPI). Details of GA tuning turn-ed out to be far less important for global optimization efficiency than using suitable ranges within which the parameters are varied. To establish these ranges, either prior knowledge can be used or successive stages of GA optimizations, each building upon the best parameter vectors and ranges found in the previous stage. We have finally arrive-ed at optimized force fields with smaller error measures than those published previously. Hence, this optimization approach will contribute to converting force-field fitting from a specialist task to an everyday commodity, even for the more difficult case of reactive force fields. © 2013 Wiley Periodicals, Inc.
BibTeX:
@article{Larsson2013a,
author = {Larsson, Henrik R. and van Duin, Adri C. T. and Hartke, Bernd},
title = {Global optimization of parameters in the reactive force field ReaxFF for SiOH},
journal = {Journal of Computational Chemistry},
year = {2013},
volume = {34},
pages = {2178-2189},
doi = {https://doi.org/10.1002/jcc.23382}
}
Fitting reactive force fields using genetic algorithms
H.R. Larsson and B. Hartke, Computer Methods in Materials Science 2013, 13, 120-126.
Abstract:
With reactive force fields it is possible to perform atomistic simulations that join the accuracy of quantum chemical treatments (including bond breaking and formation) with the ability to treat hundreds of thousands of atoms on time scales well into the nanosecond regime. To utilize this power in everyday applications requires (I) the assembly of a suitable reference data set of sufficient quality, and (II) a reliable fit of the huge and complex parameter set of a general reactive force field to these reference data. In this contribution, we show that genetic algorithms can be used to achieve goal (II). We discuss algorithm design and implementation aspects (including parallelization) and present real-life application examples.
BibTeX:
@article{Larsson2013,
author = {Larsson, Henrik R. and Hartke, Bernd},
title = {Fitting reactive force fields using genetic algorithms},
journal = {Computer Methods in Materials Science},
year = {2013},
volume = {13},
pages = {120-126},
url = {www.cmms.agh.edu.pl/abstract.php?p_id=420}
}
Approximate photochemical dynamics of azobenzene with reactive force fields
Y. Li and B. Hartke, The Journal of Chemical Physics 2013, 139, 2178.
Abstract:
We have fitted reactive force fields of the ReaxFF type to the ground and first excited electronic states of azobenzene, using global parameter optimization by genetic algorithms. Upon coupling with a simple energy-gap transition probability model, this setup allows for completely force-field-based simulations of photochemical cis→trans- and trans→cis-isomerizations of azobenzene, with qualitatively acceptable quantum yields. This paves the way towards large-scale dynamics simulations of molecular machines, including bond breaking and formation (via the reactive force field) as well as photochemical engines (presented in this work).
BibTeX:
@article{Li2013,
author = {Li, Yan and Hartke, Bernd},
title = {Approximate photochemical dynamics of azobenzene with reactive force fields},
journal = {The Journal of Chemical Physics},
year = {2013},
volume = {139},
number = {22},
pages = {2178},
doi = {https://doi.org/10.1063/1.4837237}
}
Electronic structure, adsorption geometry, and photoswitchability of azobenzene layers adsorbed on layered crystals
E. Ludwig, T. Strunskus, S. Hellmann, A. Nefedov, C. Woll, L. Kipp and K. Rossnagel, Phys. Chem. Chem. Phys. 2013, 15, 20272-20280.
Abstract:
Mono- and multilayers of the molecular photoswitch azobenzene were adsorbed on two layered transition-metal dichalcogenides, semiconducting HfS2 and metallic TiTe2, at temperatures of 80-120 K and investigated in situ using valence-band and core-level photoelectron spectroscopy as well as near-edge X-ray absorption fine structure spectroscopy. The spectroscopic results indicate similar growth modes on the two substrates. In the monolayer systems, the azobenzene molecules tend to lie flat on the surface with average tilt angles of <15[degree], whereas the multilayer systems show a larger average tilt angle of 35-45[degree], depending on substrate surface conditions. The chemical environment of azobenzene, as investigated by XPS, does not change significantly from mono- to multilayers suggesting weak adsorbate-substrate coupling for the molecular layer that forms the interface with the substrate. Irradiation with ultraviolet light with a wavelength of 365 nm leads to a partial rearrangement of the adsorbed azobenzene molecules with a trans-to-cis conversion of up to 35%.
BibTeX:
@article{Ludwig2013,
author = {Ludwig, Eric and Strunskus, Thomas and Hellmann, Stefan and Nefedov, Alexei and Woll, Christof and Kipp, Lutz and Rossnagel, Kai},
title = {Electronic structure, adsorption geometry, and photoswitchability of azobenzene layers adsorbed on layered crystals},
journal = {Phys. Chem. Chem. Phys.},
year = {2013},
volume = {15},
pages = {20272-20280},
doi = {https://doi.org/10.1039/C3CP53003E}
}
Graphene-mediated exchange coupling between a molecular spin and magnetic substrates
S. Marocchi, P. Ferriani, N.M. Caffrey, F. Manghi, S. Heinze and V. Bellini, Phys. Rev. B 2013, 88, 144407.
Abstract:
Using first-principles calculations we demonstrate sizable exchange coupling between a magnetic molecule and a magnetic substrate via a graphene layer. As a model system we consider cobaltocene (CoCp2) adsorbed on graphene deposited on Ni(111). We find that the magnetic coupling is antiferromagnetic and is influenced by the molecule structure, the adsorption geometry, and the stacking of graphene on the substrate. We show how the coupling can be tuned by the intercalation of a magnetic monolayer, such as Fe or Co, between graphene and Ni(111). We identify the leading mechanism responsible for the coupling to be the spatial and energy matching of the frontier orbitals of CoCp2 and graphene close to the Fermi level. Graphene plays the role of an electronic decoupling layer while allowing effective spin communication between molecule and substrate.
BibTeX:
@article{Marocchi2013,
author = {Marocchi, S. and Ferriani, P. and Caffrey, N. M. and Manghi, F. and Heinze, S. and Bellini, V.},
title = {Graphene-mediated exchange coupling between a molecular spin and magnetic substrates},
journal = {Phys. Rev. B},
year = {2013},
volume = {88},
pages = {144407},
doi = {https://doi.org/10.1103/PhysRevB.88.144407}
}
Formation of Self-organized Silver Nanocup-Type Structures and Their Plasmonic Absorption
Y. Mishra, R. Adelung, G. Kumar, M. Elbahri, S. Mohapatra, R. Singhal, A. Tripathi and D. Avasthi, Plasmonics 2013, 8, 811-815.
Abstract:
The present work reports on the formation of extremely low volume, silver nanocup-type structures on the surface by annealing of ultra-thin silver film on quartz in inert environment. Atomic force microscopy studies together with scanning electron microscopy confirmed the formation of Ag nanocup-type structures at the surface. A basic physical model for the formation of nanocups in terms of buckling and Oswald ripening due to surface-induced morphological instability and diffusional mass transport under thermal treatment is demonstrated. Surface plasmon resonance absorptions of nanocup structures are studied and preliminary experiment for observing the surface-enhanced Raman scattering of fullerene C70 molecules has been shown.
BibTeX:
@article{Mishra2013a,
author = {Mishra, Y.K. and Adelung, R. and Kumar, G. and Elbahri, M. and Mohapatra, S. and Singhal, R. and Tripathi, A. and Avasthi, D.K.},
title = {Formation of Self-organized Silver Nanocup-Type Structures and Their Plasmonic Absorption},
journal = {Plasmonics},
year = {2013},
volume = {8},
number = {2},
pages = {811-815},
doi = {https://doi.org/10.1007/s11468-013-9477-2}
}
Fabrication of Macroscopically Flexible and Highly Porous 3D Semiconductor Networks from Interpenetrating Nanostructures by a Simple Flame Transport Approach
Y.K. Mishra, S. Kaps, A. Schuchardt, I. Paulowicz, X. Jin, D. Gedamu, S. Freitag, M. Claus, S. Wille, A. Kovalev, S.N. Gorb and R. Adelung, Particle & Particle Systems Characterization 2013, 30, 775-783.
Abstract:
Flexible, electrically conducting, high temperature stable ceramics with very high porosities are fabricated from interpenetrated metal oxide nano-microstructures in a versatile manner in a novel flame transport synthesis approach. The Young's modulus of these networks can be tuned from wool type to rubber like based on the density, type and interconnections of the building blocks. Semiconducting behavior allows multifunctional applications like the electrical readout of the mechanical history.
BibTeX:
@article{Mishra2013,
author = {Mishra, Yogendra K. and Kaps, Sören and Schuchardt, Arnim and Paulowicz, Ingo and Jin, Xin and Gedamu, Dawit and Freitag, Stefan and Claus, Maria and Wille, Sebastian and Kovalev, Alexander and Gorb, Stanislav N. and Adelung, Rainer},
title = {Fabrication of Macroscopically Flexible and Highly Porous 3D Semiconductor Networks from Interpenetrating Nanostructures by a Simple Flame Transport Approach},
journal = {Particle & Particle Systems Characterization},
year = {2013},
volume = {30},
pages = {775-783},
doi = {https://doi.org/10.1002/ppsc.201300197}
}
Localized Surface Plasmon Resonance Investigations of Photoswitching in Azobenzene-Functionalized Self-Assembled Monolayers on Au
M. Müller, U. Jung, V. Gusak, S. Ulrich, M. Holz, R. Herges, C. Langhammer and O.M. Magnussen, Langmuir 2013, 29, 10693-10699.
Abstract:
Localized plasmon resonance (LSPR) spectroscopy, employing gold nanodisk substrates, is applied for studies of photoswitching in self-assembled monolayers of azobenzene-containing thiols. By choosing customized samples, in which the sharp LSPR resonance is well separated from the spectral regime of the molecular absorbtion bands, the photoisomerization kinetics of the adlayer can be monitored in real time. Quantitative data on the photoinduced trans-cis and cis-trans isomerization processes in inert gas atmosphere were obtained as a function of irradiation intensity and temperature, demonstrating the high sensitivity of this technique to such processes in functional adlayers.
BibTeX:
@article{Mueller0,
author = {Müller, Mathias and Jung, Ulrich and Gusak, Viktoria and Ulrich, Sandra and Holz, Michelle and Herges, Rainer and Langhammer, Christoph and Magnussen, Olaf M.},
title = {Localized Surface Plasmon Resonance Investigations of Photoswitching in Azobenzene-Functionalized Self-Assembled Monolayers on Au},
journal = {Langmuir},
year = {2013},
volume = {29},
pages = {10693-10699},
doi = {https://doi.org/10.1021/la401825f}
}
Enhanced photoswitching and ultrafast dynamics in structurally modified photochromic fulgides
F. Renth, R. Siewertsen and F. Temps, International Reviews in Physical Chemistry 2013, 32, 1-38.
Abstract:
Emerging new applications, e.g. as molecular logical devices and in superresolution imaging, have fuelled considerable interest in the design of improved fulgide photoswitches and the fundamental ultrafast processes that determine their photochemistry. This review is concerned with the basic photoswitching properties of fulgides and fulgimides. The emphasis is put on recent results on the underlying photo-induced ultrafast dynamics of chemically modified fulgides to uncover the basis for the observed changes in the photochemical behaviour upon structural variation. Particular attention is directed at the effects of selected structural motifs on the photoisomerisation pathways and the implications for a rational design of derivatives with improved switching properties. @ARTICLEISI:000305533100009, author = Bahrenburg, Julia and Roettger, Katharina and Siewertsen, Ron and Renth, Falk and Temps, Friedrich, title = Sequential photoisomerisation dynamics of the push-pull azobenzene Disperse Red 1, journal = PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES, year = 2012, volume = 11, pages = 1210-1219, number = 7, abstract = The ultrafast dynamics of the push-pull azobenzene Disperse Red 1 following photoexcitation at lambda(pump) = 475 nm in solution in 2-fluorotoluene have been probed by broadband transient absorption spectroscopy and fluorescence up-conversion spectroscopy. The measured two-dimensional spectro-temporal absorption map features a remarkable ``fast'' excited-state absorption (ESA) band at lambda approximate to 570 nm appearing directly with the excitation laser pulse and showing a sub-100 fs lifetime with a rapid spectral blue-shift. Moreover, its ultrafast decay is paralleled by rising distinctive ESA at other wavelengths. Global fits to the absorption-time profiles using a consecutive kinetic model yielded three time constants, tau(1) = 0.08 +/- 0.03 ps, tau(2) = 0.99 +/- 0.02 ps, and tau(3) = 6.0 +/- 0.1 ps. Fluorescence-time profiles were biexponential with time constants tau(1)' = 0.12 +/- 0.06 ps and tau(2)' = 0.70 +/- 0.10 ps, close to the absorption results. Based on the temporal evolution of the transient spectra, especially the ``fast'' excited-state absorption band at lambda approximate to 570 nm, and on the global kinetic analysis of the time profiles, tau(1) is assigned to an ultrafast transformation of the optically excited pi pi* state to an intermediate state, which may be the n pi* state, tau(2) to the subsequent isomerisation and radiationless deactivation time to the S-0 electronic ground state, and tau(3) to the eventual vibrational cooling of the internally ``hot'' S-0 molecules., address = THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, affiliation = Renth, F (Reprint Author), Univ Kiel, Inst Phys Chem, Olshausenstr 40, D-24098 Kiel, Germany. Bahrenburg, Julia; Roettger, Katharina; Siewertsen, Ron; Renth, Falk; Temps, Friedrich, Univ Kiel, Inst Phys Chem, D-24098 Kiel, Germany., author-email = renth@phc.uni-kiel.de temps@phc.uni-kiel.de, doc-delivery-number = 962HH, doi = 10.1039/c2pp05400k, funding-acknowledgement = Deutsche Forschungsgemeinschaft [677], funding-text = This work has been supported by the Deutsche Forschungsgemeinschaft through project A1 of the Sonderforschungsbereich 677 ``Function by Switching''., issn = 1474-905X, journal-iso = Photochem. Photobiol. Sci., keywords-plus = TRANSIENT ABSORPTION-SPECTROSCOPY; UP-CONVERSION SPECTROSCOPY; FEMTOSECOND FLUORESCENCE; SOLVENT DYNAMICS; EXCITED-STATE; S-1 STATE; AB-INITIO; ISOMERIZATION; DERIVATIVES; EXCITATION, language = English, number-of-cited-references = 50, publisher = ROYAL SOC CHEMISTRY, research-areas = Biochemistry & Molecular Biology; Biophysics; Chemistry, times-cited = 0, type = Article, unique-id = ISI:000305533100009, web-of-science-categories = Biochemistry & Molecular Biology; Biophysics; Chemistry, Physical
BibTeX:
@article{Renth2013,
author = {Renth, F and Siewertsen, R and Temps, F},
title = {Enhanced photoswitching and ultrafast dynamics in structurally modified photochromic fulgides},
journal = {International Reviews in Physical Chemistry},
year = {2013},
volume = {32},
number = {1},
pages = {1-38},
doi = {https://doi.org/10.1080/0144235X.2012.729331}
}
Iron(II) Complexes Supported by a Tetradentate Ligand Providing a Strained Equatorial Coordination Environment: Geometric and Electronic-Structural Implications
S.O. Schmidt, S. Kisslinger, C. Würtele, S. Bonnet, S. Schindler and F. Tuczek, Zeitschrift für anorganische und allgemeine Chemie 2013, 639, 2774-2778.
Abstract:
Searching for SCO compounds with tetradentate equatorial ligands suitable to surface attachment we decided to synthesize iron(II) complexes with the ligand o-bpy [o-bpy = 1,2-bis(2,2′-bipyridyl-6-yl)ethane]. For coordination in axial position three different ligands with increasing ligand field strength were considered: isothiocyanate, pyridine, and imidazole. The new iron(II) complexes [Fe(o-bpy)(NCS)2], [Fe(o-bpy)(py)2](BPh4)2, and [Fe(o-bpy)(im)2](BPh4)2 were characterized with the help of Mössbauer spectroscopy, magnetic measurements, and X-ray crystallography. The Mössbauer data and magnetic susceptibility measurements show that all three synthesized compounds are in the high-spin state between 300 and 2 K. To explain these findings DFT calculations are employed. The experimental and theoretical results indicate the presence of distortions from octahedral symmetry due to steric restrictions imposed by the o-bpy ligand, which reduce its ligand-field strength, leading to the observed S = 2 ground states.
BibTeX:
@article{Schmidt2013,
author = {Schmidt, Sven Olaf and Kisslinger, Sandra and Würtele, Christian and Bonnet, Sylvestre and Schindler, Siegfried and Tuczek, Felix},
title = {Iron(II) Complexes Supported by a Tetradentate Ligand Providing a Strained Equatorial Coordination Environment: Geometric and Electronic-Structural Implications},
journal = {Zeitschrift für anorganische und allgemeine Chemie},
year = {2013},
volume = {639},
number = {15},
pages = {2774-2778},
doi = {https://doi.org/10.1002/zaac.201300425}
}
Importance of a low-lying nπ*-state in the photo-isomerisation reaction of Z-methylfurylfulgide
J.B. Schönborn and Hartke, J. Photochem. Photobiol. A 2013, 263, 34-40.
Abstract:
Knowledge about the character of electronic states involved in ultrafast photoreactions is essential for understanding the dynamics leading to static and transient experimental spectra. Here we present a detailed study of the three lowest-energy electronic states of the photochromic switch methylfurylfulgide in its Z-form and of their changes as they approach the S1S0-conical intersection that facilitates the formation of E-methylfurylfulgide. We studied the molecular energy landscape by identifying important points along the reaction coordinate (Franck–Condon point, S1-energy minimum and S1S0-conical intersection) by state-averaged CASSCF(10,9)/6-31g(d,p) calculations, assigned the character of the three lowest electronic states at these points and verified our classifications by CASPT2(18,13) calculations in a basis of polarised triple-zeta quality for the atoms relevant to the reaction and polarised double-zeta for the others. In contrast to the E→Z interconversion, it turns out that a proper active space for the Z→E interconversion should consist not only of π orbitals but should contain also orbitals of n character. We expect this to experimentally manifest itself in visible differences between Z→E and E→Z behaviour.
BibTeX:
@article{Schoenborn2013,
author = {Schönborn, J. B. and Hartke,},
title = {Importance of a low-lying nπ*-state in the photo-isomerisation reaction of Z-methylfurylfulgide},
journal = {J. Photochem. Photobiol. A},
year = {2013},
volume = {263},
pages = {34-40},
doi = {https://doi.org/10.1016/j.jphotochem.2013.04.014}
}
Chemische Schalter als potenzielle Lernschalter
S. Schwarzer, J. Rudnik and I. Parchmann, CHEMKON 2013, 20, 175-181.
Abstract:
Eine stärkere Verknüpfung von Fachforschung, Bildung und Öffentlichkeitsarbeit bietet vielfältige Potenziale. Dieser Beitrag stellt die fachdidaktische Begleitung des Sonderforschungsbereichs 677 „Funktion durch Schalten“ vor, der molekulare Maschinen im Bereich der Nanowissenschaften beforscht. Es wird ein Schülerlaborkonzept für die Oberstufe, basierend auf dem Modell der Didaktischen Rekonstruktion, praxisnah erläutert. Für die Vorbereitung und Integration eines Schülerlaborbesuchs in den Unterricht werden entsprechende Materialien vorgestellt. Abschließend wird ein Ausblick auf empirische Untersuchungen, zu Forschungsfragen wie Erwartungen und Bewertungen des Schülerlaborbesuchs durch Schülerinnen und Schüler, gegeben.
BibTeX:
@article{Schwarzer2013a,
author = {Schwarzer, Stefan and Rudnik, Julian and Parchmann, Ilka},
title = {Chemische Schalter als potenzielle Lernschalter},
journal = {CHEMKON},
year = {2013},
volume = {20},
pages = {175-181},
doi = {https://doi.org/10.1002/ckon.201310206}
}
Amino-substituted diazocines as pincer-type photochromic switches
H. Sell, C. Näther and R. Herges, Beilstein Journal of Organic Chemistry 2013, 9, 1-7.
Abstract:
Azobenzenes are robust, reliable, and easy to synthesize photochromic switches. However, their high conformational flexibility is a disadvantage in machine-like applications. The almost free rotation of the phenyl groups can be restricted by bridging two ortho positions with a CH2CH2 group, as realized in the dihydrodibenzo diazocine framework. We present the synthesis and properties of 3,3’-amino- and 3,3’-acetamido substituted diazocines. Upon irradiation with light of 405 and 530 nm they isomerize from the cis to the trans configuration and back, and thereby perform a pincer-like motion. In the thermodynamically more stable cis isomer the lone pairs of the amino nitrogen atoms point towards each other, and in the trans form they point in opposite directions. The distance between the amino nitrogen atoms changes between 8 Å (cis) and 11 Å (trans isomer)
BibTeX:
@article{Sell2013,
author = {Hanno Sell and Christian Näther and Rainer Herges},
title = {Amino-substituted diazocines as pincer-type photochromic switches},
journal = {Beilstein Journal of Organic Chemistry},
year = {2013},
volume = {9},
pages = {1-7},
doi = {https://doi.org/10.3762/bjoc.9.1}
}
Atom für Atom
A. Sperl, J. Kröger and R. Berndt, Chemie in unserer Zeit 2013, 47, 296-299.
Abstract:
Mit Hilfe der Spitze eines Rastertunnelmikroskops wird ein einzelnes metallfreies Phthalocyanin-Molekül in ein Silber-Phthalocynanin auf einer Obefläche umgewandelt. Die Reaktionsschritte erfolgen Atom für Atom. Jedes Zwischenprodukt kann mit Hilfe von rastertunnelmikroskopischen Aufnahmen analysiert werden. Neben der schrittweisen Molekülumwandlung sind die Tautomerisierung und das H-Hüpfen, die kontrolliert durch Injektion von Elektronen induziert werden, weitere Beispiele für die Präzision eines modernen Rastertunnelmikroskops.
BibTeX:
@article{Sperl2013,
author = {Sperl, Alexander and Kröger, Jörg and Berndt, Richard},
title = {Atom für Atom},
journal = {Chemie in unserer Zeit},
year = {2013},
volume = {47},
pages = {296-299},
doi = {https://doi.org/10.1002/ciuz.201300617}
}
Pointed Carbon Fiber Ultramicroelectrodes: A New Probe Option for Electrochemical Scanning Tunneling Microscopy
J. Sripirom, S. Kuhn, U. Jung, O. Magnussen and A. Schulte, Analytical Chemistry 2013, 85, 837-842.
Abstract:
Carbon tips for in situ scanning tunneling microscopy studies in an electrochemical environment were prepared by electrochemical etching of carbon fibers and subsequent coating with electrodeposition paint and a silicone elastomer. The tips obtained were stable in acidic electrolyte and allowed high-resolution in situ imaging of the bare Au(111) electrode surface and of Au(111) covered by monolayers of the octyl-triazatriangulenium molecule.
BibTeX:
@article{Sripirom2013,
author = {Sripirom, Jiyapa and Kuhn, Sonja and Jung, Ulrich and Magnussen, Olaf and Schulte, Albert},
title = {Pointed Carbon Fiber Ultramicroelectrodes: A New Probe Option for Electrochemical Scanning Tunneling Microscopy},
journal = {Analytical Chemistry},
year = {2013},
volume = {85},
number = {2},
pages = {837-842},
doi = {https://doi.org/10.1021/ac3028432}
}
Are multivalent cluster glycosides a means of controlling ligand density of glycoarrays?
J.W. Wehner, M. Hartmann and T.K. Lindhorst, Carbohydrate Research 2013, 371, 22 - 31.
Abstract:
Bacterial adhesion to the glycocalyx of human host cells is of biological and medicinal importance. This process is often initiated by the interaction of bacterial lectins and specific carbohydrate ligands. Thus, adhesion of bacterial cells to glycosylated surfaces is a suitable model system to study various parameters of lectin-mediated carbohydrate recognition. Glycoarrays have become important tools to study such lectin-mediated carbohydrate recognition. However, it is difficult to adjust the characteristics of a specific glycoarray regarding its carbohydrate density or the clustering of sugar ligands, respectively. Thus, we have made an attempt to use synthetic cluster glycosides of different valencies to vary carbohydrate density on a polystyrene surface. A series of mono-, di- and trivalent mannosides were synthesised for immobilisation on pre-functionalised polystyrene microtiter plates and the resulting glycoarrays were tested as adhesive surfaces in mannose-specific adhesion of Escherichia coli. Our measurements give first promising hints about the potential of this approach to alter ligand density of glycoarrays in a systematic way.
BibTeX:
@article{Wehner2013,
author = {Johannes W. Wehner and Mirja Hartmann and Thisbe K. Lindhorst},
title = {Are multivalent cluster glycosides a means of controlling ligand density of glycoarrays? },
journal = {Carbohydrate Research },
year = {2013},
volume = {371},
pages = {22 - 31},
doi = {https://doi.org/10.1016/j.carres.2013.01.023}
}
Sequential photoisomerisation dynamics of the push-pull azobenzene Disperse Red 1
J. Bahrenburg, K. Roettger, R. Siewertsen, F. Renth and F. Temps, Photochem. Photobiol. Sci. 2012, 11, 1210-1219.
Abstract:
The ultrafast dynamics of the push-pull azobenzene Disperse Red 1 following photoexcitation at pump = 475 nm in solution in 2-fluorotoluene have been probed by broadband transient absorption spectroscopy and fluorescence up-conversion spectroscopy. The measured two-dimensional spectro-temporal absorption map features a remarkable ``fast'' excited-state absorption (ESA) band at λ approximate to 570 nm appearing directly with the excitation laser pulse and showing a sub-100 fs lifetime with a rapid spectral blue-shift. Moreover, its ultrafast decay is paralleled by rising distinctive ESA at other wavelengths. Global fits to the absorption-time profiles using a consecutive kinetic model yielded three time constants, 1= 0.08 ± 0.03 ps, tau_2 = 0.99 +/- 0.02 ps, and tau_3 = 6.0 ± 0.1 ps. Fluorescence-time profiles were biexponential with time constants 1^′ = 0.12 ± 0.06 ps and 2^′ = 0.70 ± 0.10 ps, close to the absorption results. Based on the temporal evolution of the transient spectra, especially the ``fast'' excited-state absorption band at lambda approximate to 570 nm, and on the global kinetic analysis of the time profiles,1 is assigned to an ultrafast transformation of the optically excited pi pi^state to an intermediate state, which may be the n pi^state, 2 to the subsequent isomerisation and radiationless deactivation time to the S_0 electronic ground state, and 3 to the eventual vibrational cooling of the internally ``hot'' S_0$ molecules.
BibTeX:
@article{Bahrenburg2012,
author = {Bahrenburg, Julia and Roettger, Katharina and Siewertsen, Ron and Renth, Falk and Temps, Friedrich},
title = {Sequential photoisomerisation dynamics of the push-pull azobenzene Disperse Red 1},
journal = {Photochem. Photobiol. Sci.},
year = {2012},
volume = {11},
number = {7},
pages = {1210-1219},
doi = {https://doi.org/10.1039/c2pp05400k}
}
FeIII Spin-Crossover Complexes with Photoisomerizable Ligands: Experimental and Theoretical Studies on the Ligand-Driven Light-Induced Spin Change Effect
A. Bannwarth, S.O. Schmidt, G. Peters, F.D. Sönnichsen, W. Thimm, R. Herges and F. Tuczek, Eur. J. Inorg. Chem. 2012, 2776-2783.
Abstract:
Conflicting results have been reported with respect to the photoinduced switching of the magnetic properties of [FeIII(salten)]+ complexes [salten = 4-azaheptamethylene-1,7-bis(salicylideneiminate)] coordinated by photoisomerizable ligands. In order to address this problem, two FeIII complexes [Fe(salten)(3-azpy)]BPh4 (1) and [Fe(salten)(4-azpy)]BPh4 (2) have been synthesized and characterized by various physicochemical methods (azpy = phenylazopyridine). Both 1 and 2 exhibit a low spin (S = 1/2) to high spin (HS, S = 5/2) transition in the solid state. In solution at room temperature both complexes are predominantly HS. Upon exposure to 310 (trans-cis) and 440 nm radiation (cis-trans) the free and coordinated 3- and 4-azpy ligands undergo a reversible cis–trans isomerization. For 2 a corresponding reduction of the HS fraction 2 % is observed, whereas in 1 no effect is observed. Extensive DFT calculations, which employ different functionals and basis sets, explain this experimental result. The consequences of these findings with respect to the design of spin-switchable iron(III) complexes with photoactive ligands are discussed.
BibTeX:
@article{Bannwarth2012,
author = {Bannwarth, Alexander and Schmidt,Sven Olaf and Peters, Gerhard and Sönnichsen, Frank D. and Thimm, Wulf and Herges, Rainer and Tuczek, Felix},
title = {FeIII Spin-Crossover Complexes with Photoisomerizable Ligands: Experimental and Theoretical Studies on the Ligand-Driven Light-Induced Spin Change Effect},
journal = {Eur. J. Inorg. Chem.},
year = {2012},
pages = {2776-2783},
doi = {https://doi.org/10.1002/ejic.201101227}
}
Sweet switches: azobenzene glycoconjugates synthesized by click chemistry
V. Chandrasekaran and T.K. Lindhorst, Chem. Commun. 2012, 48, 7519-7521.
Abstract:
Azobenzene glycoconjugates can be switched between two isomeric states, E and Z, to change the spatial orientation of the conjugated carbohydrate ligands. Mono-, di- and trivalent azobenzene glycoconjugates were synthesized using click chemistry and their photochromic properties determined. Multivalency effects were observed in photoisomerisation.
BibTeX:
@article{Chandrasekaran2012,
author = {Chandrasekaran, Vijayanand and Lindhorst, Thisbe K.},
title = {Sweet switches: azobenzene glycoconjugates synthesized by click chemistry},
journal = {Chem. Commun.},
year = {2012},
volume = {48},
pages = {7519-7521},
doi = {https://doi.org/10.1039/C2CC33542E}
}
Electron-Induced Spin Crossover of Single Molecules in a Bilayer on Gold
T.G. Gopakumar, F. Matino, H. Naggert, A. Bannwarth, F. Tuczek and R. Berndt, Angew. Chem. Int. Ed. 2012, 51, 6262-6266.
Abstract:
Single molecules of the iron(II) complex [Fe(bpz)2phen] (phen=1,10-phenanthroline, bpz=dihydrobis(pyrazolyl)borate) are reversibly switched between low spin and high spin by electron-induced spin crossover (ELIESST) in a bilayer on gold, as revealed by STM.
BibTeX:
@article{Gopakumar2012,
author = {Gopakumar, Thiruvancheril G. and Matino, Francesca and Naggert, Holger and Bannwarth, Alexander and Tuczek, Felix and Berndt, Richard},
title = {Electron-Induced Spin Crossover of Single Molecules in a Bilayer on Gold},
journal = {Angew. Chem. Int. Ed.},
year = {2012},
volume = {51},
pages = {6262-6266},
doi = {https://doi.org/10.1002/anie.201201203}
}
Transfer of Cl Ligands between Adsorbed Iron Tetraphenylporphyrin Molecules
T.G. Gopakumar, H. Tang, J. Morillo and R. Berndt, Journal of the American Chemical Society 2012, 134, 11844-11847.
Abstract:
Iron tetraphenylporphyrin chloride (FeTPPCl) adsorbed on a Au(111) substrate is investigated using low-temperature scanning tunneling microscopy. Cl is controllably transferred between the Fe center of a selected molecule and the tip of the microscope without disrupting the surrounding molecular pattern. Cl abstraction from FeTPPCl is triggered by removing an electron from the highest occupied molecular orbital. Density functional calculations suggest that the reaction involves a change in the oxidation state of the Fe ion.
BibTeX:
@article{Gopakumar2012a,
author = {Gopakumar, Thiruvancheril G. and Tang, Hao and Morillo, Joseph and Berndt, Richard},
title = {Transfer of Cl Ligands between Adsorbed Iron Tetraphenylporphyrin Molecules},
journal = {Journal of the American Chemical Society},
year = {2012},
volume = {134},
number = {29},
pages = {11844-11847},
doi = {https://doi.org/10.1021/ja302589z}
}
Glycoarrays by a New Tandem Noncovalent–Covalent Modification of Polystyrene Microtiter Plates and their Interrogation with Live Cells
C. Grabosch, K. Kolbe and T.K. Lindhorst, ChemBioChem 2012, 13, 1874-1879.
Abstract:
Glycoarrays—easier than ever: Glycoarrays were fabricated on polystyrene microtiter plates with great ease by using a tandem process that combined hydrophobic adsorption and thiourea bridging. They were validated by testing specific bacterial adhesion and its inhibition.
BibTeX:
@article{Grabosch2012,
author = {Grabosch, Carsten and Kolbe, Katharina and Lindhorst, Thisbe K.},
title = {Glycoarrays by a New Tandem Noncovalent–Covalent Modification of Polystyrene Microtiter Plates and their Interrogation with Live Cells},
journal = {ChemBioChem},
year = {2012},
volume = {13},
pages = {1874-1879},
doi = {https://doi.org/10.1002/cbic.201200365}
}
Electronic Ground-State and Orbital Ordering of Iron Phthalocyanine on H/Si(111) Unraveled by Spatially Resolved Tunneling Spectroscopy
M. Gruyters, T. Pingel, T.G. Gopakumar, N. Néel, C. Schütt, F. Köhler, R. Herges and R. Berndt, The Journal of Physical Chemistry C 2012, 116, 20882-20886.
Abstract:
The electronic properties of FePc molecules adsorbed on hydrogen-passivated Si(111) surfaces are investigated by scanning tunneling microscopy at low temperatures. Spatially resolved spectroscopy reveals a significant variation of the electronic states at different positions above the molecule. The highest occupied ligand- and metal-based orbitals of FePc are determined by pronounced peaks in the tunneling spectra and voltage-dependent changes in the microscopic images. Comparison with density functional theory calculations indicates that the electronic ground state is an 3A1g state.
BibTeX:
@article{Gruyters2012,
author = {Gruyters, M. and Pingel, T. and Gopakumar, T. G. and Néel, N. and Schütt, Ch. and Köhler, F. and Herges, R. and Berndt, R.},
title = {Electronic Ground-State and Orbital Ordering of Iron Phthalocyanine on H/Si(111) Unraveled by Spatially Resolved Tunneling Spectroscopy},
journal = {The Journal of Physical Chemistry C},
year = {2012},
volume = {116},
number = {39},
pages = {20882-20886},
doi = {https://doi.org/10.1021/jp3058433}
}
Conductance fingerprints of noncollinear magnetic states in single-atom contacts: A first-principles Wannier-functions study
B. Hardrat, F. Freimuth, S. Heinze and Y. Mokrousov, Phys. Rev. B 2012, 86, 165449.
Abstract:
We present a first-principles computational scheme for investigating the ballistic transport properties of one-dimensional nanostructures with noncollinear magnetic order. The electronic structure is obtained within density functional theory as implemented in the full-potential linearized augmented plane-wave method and mapped to a tight-binding-like transport Hamiltonian via noncollinear Wannier functions. The conductance is then computed based on the Landauer formula using the Green's function method. As a first application, we study the conductance between two ferromagnetic Co monowires terminated by single Mn apex atoms as a function of Mn-Mn separation. We vary the Mn-Mn separation from the contact (about 2.5 to 5 Å) to the far tunneling regime (5 to 10 Å). The magnetization direction of the Co electrodes is chosen either in parallel or antiparallel alignment and we allow for different spin configurations of the two Mn spins. In the tunneling and into the contact regime, the conductance is dominated by s-dz2 states. In the close contact regime (below 3.5 Å), there is an additional contribution for a parallel magnetization alignment from the dxz and dyz states which give rise to an increase of the magnetoresistance as it is absent for antiparallel magnetization. If we allow the Mn spins to relax, a noncollinear spin state is formed close to contact due to the competition of ferromagnetic coupling between Mn and Co and antiferromagnetic coupling between the Mn spins. We demonstrate that the transition from a collinear to such a noncollinear spin structure as the two Mn atoms approach leaves a characteristic dip in the distance-dependent conductance and magnetoresistance of the junction. We explain this modification of the spin-valve effect due to the noncollinear spin state based on the spin-dependent hybridization between the dxz,yz states of the Mn spins and their coupling to the Co electrodes.
BibTeX:
@article{Hardrat2012,
author = {Hardrat, Björn and Freimuth, Frank and Heinze, Stefan and Mokrousov, Yuriy},
title = {Conductance fingerprints of noncollinear magnetic states in single-atom contacts: A first-principles Wannier-functions study},
journal = {Phys. Rev. B},
year = {2012},
volume = {86},
pages = {165449},
doi = {https://doi.org/10.1103/PhysRevB.86.165449}
}
One-dimensional ballistic transport with FLAPW Wannier functions
B. Hardrat, N.-P. Wang, F. Freimuth, Y. Mokrousov and S. Heinze, Phys. Rev. B 2012, 85, 245412.
Abstract:
We present an implementation of the ballistic Landauer-Büttiker transport scheme in one-dimensional systems based on density functional theory calculations within the full-potential linearized augmented plane-wave (FLAPW) method. In order to calculate the conductance within the Green's function method, we map the electronic structure from the extended states of the FLAPW calculation to Wannier functions, which constitute a minimal localized basis set. Our approach benefits from the high accuracy of the underlying FLAPW calculations, allowing us to address the complex interplay of structure, magnetism, and spin-orbit coupling and is ideally suited to study spin-dependent electronic transport in one-dimensional magnetic nanostructures. To illustrate our approach, we study ballistic electron transport in nonmagnetic Pt monowires with a single stretched bond including spin-orbit coupling, and in ferromagnetic Co monowires with different collinear magnetic alignment of the electrodes with the purpose of analyzing the magnetoresistance when going from tunneling to the contact regime. We further investigate spin-orbit scattering due to an impurity atom. We consider two configurations: a Co atom in a Pt monowire and vice versa. In both cases, the spin-orbit induced band mixing leads to a change of the conductance upon switching the magnetization direction from along the chain axis to perpendicular to it. The main contribution stems from ballistic spin scattering for the magnetic Co impurity in the nonmagnetic Pt monowire, and for the Pt scatterer in the magnetic Co monowire from the band formed from states with dxy and dx2−y2 orbital symmetry. We quantify this effect by calculating the ballistic anisotropic magnetoresistance, which displays values up to as much as 7% for ballistic spin scattering and gigantic values of around 100% for the Pt impurity in the Co wire. In addition, we show that the presence of a scatterer can reduce as well as increase the ballistic anisotropic magnetoresistance.
BibTeX:
@article{Hardrat2012a,
author = {Hardrat, Björn and Wang, Neng-Ping and Freimuth, Frank and Mokrousov, Yuriy and Heinze, Stefan},
title = {One-dimensional ballistic transport with FLAPW Wannier functions},
journal = {Phys. Rev. B},
year = {2012},
volume = {85},
pages = {245412},
doi = {https://doi.org/10.1103/PhysRevB.85.245412}
}
Saccharide-Modified Nanodiamond Conjugates for the Efficient Detection and Removal of Pathogenic Bacteria
M. Hartmann, P. Betz, Y. Sun, S.N. Gorb, T.K. Lindhorst and A. Krueger, Chemistry – A European Journal 2012, 18, 6485-6492.
Abstract:
The detection and removal of bacteria, such as E. coli in aqueous environments by using safe and readily available means is of high importance. Here we report on the synthesis of nanodiamonds (ND) covalently modified with specific carbohydrates (glyco–ND) for the precipitation of type 1 fimbriated uropathogenic E. coli in solution by mechanically stable agglutination. The surface of the diamond nanoparticles was modified by using a Diels–Alder reaction followed by the covalent grafting of the respective glycosides. The resulting glyco–ND samples are fully dispersible in aqueous media and show a surface loading of typically 0.1 mmol g−1. To probe the adhesive properties of various ND samples we have developed a new sandwich assay employing layers of two bacterial strains in an array format. Agglutination experiments in solution were used to distinguish unspecific interactions of glyco–ND with bacteria from specific ones. Two types of precipitates in solution were observed and characterized in detail by light and electron microscopy. Only by specific interactions mechanically stable agglutinates were formed. Bacteria could be removed from water by filtration of these stable agglutinates through 10 μm pore-size filters and the ND conjugate could eventually be recovered by addition of the appropriate carbohydrate. The application of glycosylated ND allows versatile and facile detection of bacteria and their efficient removal by using an environmentally and biomedically benign material.
BibTeX:
@article{Hartmann2012a,
author = {Hartmann, Mirja and Betz, Patrick and Sun, Yuchen and Gorb, Stanislav N. and Lindhorst, Thisbe K. and Krueger, Anke},
title = {Saccharide-Modified Nanodiamond Conjugates for the Efficient Detection and Removal of Pathogenic Bacteria},
journal = {Chemistry – A European Journal},
year = {2012},
volume = {18},
pages = {6485-6492},
doi = {https://doi.org/10.1002/chem.201104069}
}
Inhibition of bacterial adhesion to live human cells: Activity and cytotoxicity of synthetic mannosides
M. Hartmann, H. Papavlassopoulos, V. Chandrasekaran, C. Grabosch, F. Beiroth, T.K. Lindhorst and C. Röhl, FEBS\ Letters 2012, 586, 1459 - 1465.
Abstract:
Bacterial adhesion to glycosylated surfaces is a key issue in human health and disease. Inhibition of bacterial adhesion by suitable carbohydrates could lead to an anti-adhesion therapy as a novel approach against bacterial infections. A selection of five α-mannosides has been evaluated as inhibitors of bacterial adhesion to the polysaccharide mannan, as well as to the surface of live human HT-29 cells. Cell toxicity studies were performed to identify the therapeutic window for a potential in vivo-application of the tested carbohydrates. A previously published mannosidic squaric acid diamide was shown to be exceptionally effective as inhibitor of the bacterial lectin FimH.
BibTeX:
@article{Hartmann2012,
author = {Mirja Hartmann and Heike Papavlassopoulos and Vijayanand Chandrasekaran and Carsten Grabosch and Femke Beiroth and Thisbe K. Lindhorst and Claudia Röhl},
title = {Inhibition of bacterial adhesion to live human cells: Activity and cytotoxicity of synthetic mannosides },
journal = {FEBS\ Letters },
year = {2012},
volume = {586},
pages = {1459 - 1465},
doi = {https://doi.org/10.1016/j.febslet.2012.03.059}
}
Force and conductance during contact formation to a C 60 molecule
N. Hauptmann, F. Mohn, L. Gross, G. Meyer, T. Frederiksen and R. Berndt, New Journal of Physics 2012, 14, 073032.
Abstract:
Force and conductance were simultaneously measured during the formation of Cu–C 60 and C 60 –C 60 contacts using a combined cryogenic scanning tunneling and atomic force microscope. The contact geometry was controlled with submolecular resolution. The maximal attractive forces measured for the two types of junctions were found to differ significantly. We show that the previously reported values of the contact conductance correspond to the junction being under maximal tensile stress.
BibTeX:
@article{Hauptmann2012,
author = {Nadine Hauptmann and Fabian Mohn and Leo Gross and Gerhard Meyer and Thomas Frederiksen and Richard Berndt},
title = {Force and conductance during contact formation to a C 60 molecule},
journal = {New Journal of Physics},
year = {2012},
volume = {14},
number = {7},
pages = {073032},
doi = {https://doi.org/10.1088/1367-2630/14/7/073032}
}
Tunable broadband plasmonic perfect absorber at visible frequency
M. Hedayati, F. Faupel and M. Elbahri, Applied Physics A 2012, 109, 769-773.
Abstract:
Metamaterials and plasmonics as a new pioneering field in photonics joins the features of photonics and electronics by coupling photons to conduction electrons of a metal as surface plasmons (SP). This concept has been implemented for a variety of applications including negative index of refraction, magnetism at visible frequency, cloaking devices amongst others. In the present work, we used plasmonic hybrid material in order to design and fabricate a broad-band perfect plasmonic metamaterial absorber in a stack of metal and Copper-PTFE (Polytetrafluoroethylene) nanocomposite showing an average absorbance of 97.5 % in the whole visible spectrum. Our experimental results showed that the absorption peak of the stacks can be tuned upon varying the thickness and type of the spacer layer due to the sensitivity of plasmon resonance to its environment. To the best of our knowledge, this is the first report of a plasmonic metamaterial absorber based on copper with absorption around 100 % in the entire visible and near-Infrared (NIR).
BibTeX:
@article{Hedayati2012,
author = {Hedayati, MehdiKeshavarz and Faupel, Franz and Elbahri, Mady},
title = {Tunable broadband plasmonic perfect absorber at visible frequency},
journal = {Applied Physics A},
year = {2012},
volume = {109},
number = {4},
pages = {769-773},
doi = {https://doi.org/10.1007/s00339-012-7344-1}
}
Reversible switching in self-assembled monolayers of azobenzene thiolates on Au (111) probed by threshold photoemission.
N. Heinemann, J. Grunau, T. Leissner, O. Andreyev, S. Kuhn, U. Jung, D. Zargarani, R. Herges, O. Magnussen and M. Bauer, Chem. Phys. 2012, 402, 22-28.
Abstract:
The reversible photo- and thermally activated isomerization of the mol. switch 3-(4-(4-Hexyl-phenylazo)-phenoxy)-propane-1-thiol (ABT, short for AzoBenzeneThiol) deposited by self-assembly from soln. on Au (111) was studied using laser-based photoelectron spectroscopy. Differences in the mol. dipole moment characteristic for the trans and the cis isomer of ABT were monitored via changes in the sample work function, accessible by detection of the threshold energy for photoemission. A quant. anal. of the authors' data shows that the fraction of mols. within the densely packed monolayer that undergoes a switching process is of the order of 1%. This result indicates the relevance of substrate and film defects required to overcome the steric or electronic hindrance of the isomerization reaction in a densely packed monolayer.
BibTeX:
@article{Heinemann2012,
author = {Heinemann, Nils and Grunau, Jan and Leissner, Till and Andreyev, Oleksiy and Kuhn, Sonja and Jung, Ulrich and Zargarani, Dordaneh and Herges, Rainer and Magnussen, Olaf and Bauer, Michael.},
title = {Reversible switching in self-assembled monolayers of azobenzene thiolates on Au (111) probed by threshold photoemission.},
journal = {Chem. Phys.},
year = {2012},
volume = {402},
pages = {22-28},
doi = {https://doi.org/10.1016/j.chemphys.2012.03.025}
}
Molecular Switch
R. Herges, O. Jansen, F. Tuczek and S. Venkatamarani, 2012, .
Abstract:
Photosensitive molecular switch, having a chelate ligand, a metal ion bonded coordinatively to the chelate ligand, the metal ion being selected from the group of metal ions consisting of Mn2+, Mn3+, Fe2+, Fe3+, Co2+ and ?i2+, a photochromic system which is bonded covalently to the chelate ligand and can be isomerized by irradiation, this system being bonded coordinatively to the metal ion in one configuration and not bonded to the metal ion in the other configuration.
BibTeX:
@patent{Herges2012,
author = {Herges, Rainer and Jansen, Olav and Tuczek, Felix and Venkatamarani, Sugumar},
title = {Molecular Switch},
year = {2012},
number = {WO 2012022299 A1 20120223.},
url = {http://worldwide.espacenet.com/publicationDetails/biblio?CC=WO&NR=2012022299&KC=&FT=E&locale=en_EP}
}
Photosensitive metal porphyrin complexes with pendant photoisomerizable chelate arm as photochromic molecular switches undergoing photoinduced spin transition.
R. Herges, O. Jansen, F. Tuczek and S. Venkatamarani, 2012, .
BibTeX:
@patent{Herges2012a,
author = {Herges, Rainer and Jansen, Olav and Tuczek, Felix and Venkatamarani, Sugumar},
title = {Photosensitive metal porphyrin complexes with pendant photoisomerizable chelate arm as photochromic molecular switches undergoing photoinduced spin transition.},
year = {2012},
number = {DE 102010034496 A1 20120216.}
}
The growth and electronic structure of azobenzene-based functional molecules on layered crystals
J. Iwicki, E. Ludwig, J. Buck, M. Kalläne, F. Köhler, R. Herges, L. Kipp and K. Rossnagel, Journal of Physics: Condensed Matter 2012, 24, 394011.
Abstract:
In situ ultraviolet photoelectron spectroscopy is used to study the growth of ultrathin films of azobenzene-based functional molecules (azobenzene, Disperse Orange 3 and a triazatriangulenium platform with an attached functional azo-group) on the layered metal TiTe 2 and on the layered semiconductor HfS 2 at liquid nitrogen temperatures. Effects of intermolecular interactions, of the substrate electronic structure, and of the thermal energy of the sublimated molecules on the growth process and on the adsorbate electronic structure are identified and discussed. A weak adsorbate–substrate interaction is particularly observed for the layered semiconducting substrate, holding the promise of efficient molecular photoswitching.
BibTeX:
@article{Iwicki2012,
author = {J Iwicki and E Ludwig and J Buck and M Kalläne and F Köhler and R Herges and L Kipp and K Rossnagel},
title = {The growth and electronic structure of azobenzene-based functional molecules on layered crystals},
journal = {Journal of Physics: Condensed Matter},
year = {2012},
volume = {24},
pages = {394011},
doi = {https://doi.org/10.1088/0953-8984/24/39/394011}
}
Joining the Un-Joinable: Adhesion Between Low Surface Energy Polymers Using Tetrapodal ZnO Linkers
X. Jin, J. Strueben, L. Heepe, A. Kovalev, Y.K. Mishra, R. Adelung, S.N. Gorb and A. Staubitz, Advanced Materials 2012, 24, 5676-5680.
Abstract:
Tetrapodal ZnO crystals are used for mechanical interlocking of PTFE and cross-linked PDMS, classically non-adhesive polymers. This novel approach is straightforward and easily applicable and leads to a peel strength which is higher than 200 N m−1 without chemical modification of the surfaces. The shape of these fillers emerged as a crucial aspect of the interlocking mechanism.
BibTeX:
@article{Jin2012,
author = {Jin, Xin and Strueben, Jan and Heepe, Lars and Kovalev, Alexander and Mishra, Yogendra K. and Adelung, Rainer and Gorb, Stanislav N. and Staubitz, Anne},
title = {Joining the Un-Joinable: Adhesion Between Low Surface Energy Polymers Using Tetrapodal ZnO Linkers},
journal = {Advanced Materials},
year = {2012},
volume = {24},
pages = {5676-5680},
doi = {https://doi.org/10.1002/adma.201201780}
}
Photoswitching of Azobenzene-Functionalized Molecular Platforms on Au Surfaces
U. Jung, C. Schütt, O. Filinova, J. Kubitschke, R. Herges and O. Magnussen, The Journal of Physical Chemistry C 2012, 116, 25943-25948.
Abstract:
The photo- and thermally induced switching of well-ordered molecular arrays of free-standing functional groups, formed by self-assembly on Au surfaces, were studied by photoelectrochemical methods (cyclic voltammetry, chronoamperometry) and surface plasmon resonance spectroscopy. These molecular adlayers exhibit azobenzene functions mounted vertically on the surface via molecular platforms on the basis of triazatriangulenium. Detailed quantitative studies of the switching kinetics revealed that the photoinduced trans–cis isomerization of the azobenzene groups in these adlayers proceeds very fast and highly reversible. Cis–trans backisomerization by thermal relaxation occurs surprisingly 4–5 orders of magnitude faster than in solution. A rapid thermal cis–trans relaxation that dominates over the photoinduced processes is also supported by the pronounced increase of the cis fraction in the adlayers with irradiation intensity and the weak dependence of the isomerization time constants on the intensity. In complementary density functional theory calculations of the cis isomer on a Au cluster, no significant electron density depletion of the azo moiety, but strong electronic coupling of the switchable group with the Au substrate, were found. We propose that the latter leads to a spin exchange between conduction electrons in the metal and the azo moiety, enabling a relaxation mechanism that is forbidden for the free molecule.
BibTeX:
@article{Jung2012,
author = {Jung, Ulrich and Schütt, Christian and Filinova, Olena and Kubitschke, Jens and Herges, Rainer and Magnussen, Olaf},
title = {Photoswitching of Azobenzene-Functionalized Molecular Platforms on Au Surfaces},
journal = {The Journal of Physical Chemistry C},
year = {2012},
volume = {116},
pages = {25943-25948},
doi = {https://doi.org/10.1021/jp310451c}
}
Charge Contribution to the Adhesion Performance of Polymeric Microstructures
A. Kovalev and S.N. Gorb, Tribology Letters 2012, 48, 103-109.
Abstract:
Strong attachment of many insects with microstructured attachment pads is due to the Van der Waals interactions or/and the capillary forces between the pads and substrates. To establish initial contact between two surfaces a certain normal force should be applied. The presence of the charges on surfaces could facilitate or impede the initial contact formation. In this study, forces appearing due to the contact electrification of microstructured material mimicking beetle adhesive pads were measured and their influence on the contact formation was discussed. The experiments have clearly demonstrated that static charges contribute to an initial contact establishment in materials with the mushroom-shaped microstructure, whereas Van der Waals interactions or/and capillary forces have the main contribution at pull-off. A simple model was successfully used for data analysis and extraction information about the charge distribution. The effect of the jump-in due to the electrostatic interaction has to be considered during the development of further implementation of biologically inspired microstructured adhesives.
BibTeX:
@article{Kovalev2012,
author = {Kovalev, AlexanderE. and Gorb, Stanislav N.},
title = {Charge Contribution to the Adhesion Performance of Polymeric Microstructures},
journal = {Tribology Letters},
year = {2012},
volume = {48},
pages = {103-109},
doi = {https://doi.org/10.1007/s11249-012-0024-7}
}
Monitoring magnetostriction by a quantum tunnelling strain sensor
A. Kulkarni, B. Henkel, C. Bechtold, V. Zaporojtchenko, T. Strunskus, E. Quandt and F. Faupel, Sensors and Actuators: A. Physical 2012, 183, 28-33.
Abstract:
Hybrid materials offer the unique possibility to combine different functionalities of each component to obtain new classes of actuators or sensors. The hybrid material presented here consists of a macroscopic Terfenol-D crystal and a functional nanocomposite layer attached to its surface. The functional nanocomposite layer is made of polymer and Au nanoparticles in a regime near to the percolation threshold and embedded just below the polymer surface. Magnetically induced strain in the highly magnetostrictive Terfenol-D crystal leads to a change in interparticle distance between the metal nanoparticles and hence a change in quantum tunnelling properties through the two dimensional network of the Au nanoparticles. The electrical resistance of the nanocomposite layer allows direct measurement of the magnetically induced strain with a maximum change of 6% and can thus be used as a feedback sensor for the magnetostrictive actuator.
BibTeX:
@article{Kulkarni2012,
author = {Kulkarni, Amit and Henkel, Bodo and Bechtold, Christoph and Zaporojtchenko, Vladimir and Strunskus, Thomas and Quandt, Eckhard and Faupel, Franz},
title = {Monitoring magnetostriction by a quantum tunnelling strain sensor},
journal = {Sensors and Actuators: A. Physical},
year = {2012},
volume = {183},
pages = {28-33},
doi = {https://doi.org/10.1016/j.sna.2012.06.010}
}
Systematic Investigation of Porous Inorganic-Organic Hybrid Compounds with Photo-Switchable Properties
A. Modrow, M. Feyand, D. Zargarani, R. Herges and N. Stock, Zeitschrift für anorganische und allgemeine Chemie 2012, 638, 2138-2143.
Abstract:
Four new compounds [Co2(NDC)2(AzBIPY)] (1), [Cu2(NDC)2(AzBIPY)] (2), [Zn2(BPDC)2(AzBIPY)] (3) and [Zn2(CCA)2(AzBIPY)] (4) (with H2NDC: 2, 6-naphthalenedicarboxylic acid, AzBIPY: 3-azo-phenyl-4, 4′-bipyridine, H2BPDC: 4, 4′-biphenyl-dicarboxylic acid and H2CCA: 4-carboxy-cinnamic acid) were synthesized and characterized. All compounds have paddle-wheel units and photo switchable linker molecules in common. In all four compounds the azo group of the AzBIPY linker molecule protrudes into the pores. For compound 1 and 2 isomerization can be accomplished upon irradiation with UV light (λ = 365 nm) to switch the thermodynamically stable trans-isomer into the cis-isomer. Back switching can be achieved thermally or by irradiation with visible light (λ = 455 nm).
BibTeX:
@article{Modrow2012,
author = {Modrow, Antje and Feyand, Mark and Zargarani, Dordaneh and Herges, Rainer and Stock, Norbert},
title = {Systematic Investigation of Porous Inorganic-Organic Hybrid Compounds with Photo-Switchable Properties},
journal = {Zeitschrift für anorganische und allgemeine Chemie},
year = {2012},
volume = {638},
pages = {2138-2143},
doi = {https://doi.org/10.1002/zaac.201200048}
}
Introducing a photo-switchable azo-functionality inside Cr-MIL-101-NH2 by covalent post-synthetic modification
A. Modrow, D. Zargarani, R. Herges and N. Stock, Dalton Trans. 2012, 41, 8690-8696.
Abstract:
For the first time an azo functionality was covalently introduced into a MOF by post-synthetic modification. The reaction of Cr-MIL-101-NH2 with p-phenylazobenzoylchloride (1) and 4-(phenylazo)phenylisocyanate (2) as the reactants led to the compounds Cr-MIL-101_amide and Cr-MIL-101_urea, with the azo groups protruding into the mesoporous cages. XRPD and N2 sorption measurements confirm the intactness of the framework and the successful covalent modification was proven by IR- and NMR-spectroscopy. Furthermore, cis/trans isomerisation upon irradiation with light was demonstrated by UV/Vis spectroscopy. More distinct changes in the UV/Vis spectra were observed for Cr-MIL-101_amide compared to Cr-MIL-101_urea, while the degree of functionalization, i.e. the number of reacted NH2-groups, seems to have a less pronounced effect. The variation of the sorption properties due to the cis/trans isomerisation was proven by methane adsorption measurements.
BibTeX:
@article{Modrow2012a,
author = {Modrow, Antje and Zargarani, Dordaneh and Herges, Rainer and Stock, Norbert},
title = {Introducing a photo-switchable azo-functionality inside Cr-MIL-101-NH2 by covalent post-synthetic modification},
journal = {Dalton Trans.},
year = {2012},
volume = {41},
pages = {8690-8696},
doi = {https://doi.org/10.1039/C2DT30672G}
}
Simulating a Molecular Machine in Action
T. Raeker, N.O. Carstensen and B. Hartke, The Journal of Physical Chemistry A 2012, 11241-11248.
Abstract:
Using QM/MM methods, we have simulated the action of a simple molecular machine, a cilium. It consists of a platform for surface mounting, a photochemical motor unit, and a tail-like effector that amplifies the small-scale conformational change of the motor unit into a larger-scale beating motion usable for molecular transport. In this proof-of-principle application, we show that the techniques used here make it possible to perform such simulations within reasonable real time, if the device action is sufficiently fast. Additionally, we show that this molecular device actually works as intended for one isomerization direction. For the other direction, results are inconclusive, possibly because the total propagation times we can afford are too short to capture the complete event.
BibTeX:
@article{Raeker2012,
author = {Raeker, Tim and Carstensen, Niss Ole and Hartke, Bernd},
title = {Simulating a Molecular Machine in Action},
journal = {The Journal of Physical Chemistry A},
year = {2012},
pages = {11241-11248},
doi = {https://doi.org/10.1021/jp305258b}
}
Ultrafast electronic deactivation dynamics of the rare natural nucleobase hypoxanthine
K. Röttger, R. Siewertsen and F. Temps, Chemical Physics Letters 2012, 536, 140-146.
Abstract:
The electronic deactivation of the 6-oxopurine derivative hypoxanthine, its nucleoside inosine and the nucleotide inosine monophosphate have been studied by femtosecond time-resolved spectroscopy after ππ∗ photoexcitation at λ&#xa0;=&#xa0;260&#xa0;nm. The development of a highly sensitive parallel broadband (near-UV/VIS) and single-color (deep-UV) transient absorption setup enabled us to monitor the excited-state decay and the ground-state recovery dynamics in one and the same experiment. The measurements revealed similar relaxation behavior, with time constants of τ1&#xa0;≲&#xa0;0.1&#xa0;ps, τ2&#xa0;≈&#xa0;0.21&#xa0;±&#xa0;0.08&#xa0;ps and τ3&#xa0;≈&#xa0;1.8&#xa0;±&#xa0;0.4&#xa0;ps, for all three investigated molecules. The observed dynamics are assumed to take place through a conical intersection involving an out-of-plane puckering mode of the six-membered ring similar to guanine.
BibTeX:
@article{Roettger2012,
author = {Katharina Röttger and Ron Siewertsen and Friedrich Temps},
title = {Ultrafast electronic deactivation dynamics of the rare natural nucleobase hypoxanthine},
journal = {Chemical Physics Letters},
year = {2012},
volume = {536},
pages = {140-146},
doi = {https://doi.org/10.1016/j.cplett.2012.03.106}
}
Single-Molecule Force-Clamp Experiments Reveal Kinetics of Mechanically Activated Silyl Ester Hydrolysis
S.W. Schmidt, P. Filippov, A. Kersch, M.K. Beyer and H. Clausen-Schaumann, ACS Nano 2012, 6, 1314-1321.
Abstract:
We have investigated the strength of silyl ester bonds formed between carboxymethylated amylose (CMA) molecules and silane-functionalized silicon oxide surfaces using AFM-based single-molecule force spectroscopy in the force-clamp mode. Single tethered CMA molecules were picked up, and bond lifetimes were determined at constant clamp forces of 0.8, 1.0, and 1.2 nN at seven temperatures between 295 and 320 K at pH 2.0. The results reveal biexponential rupture kinetics. To obtain the reaction rate constants for each force and temperature individually, the results were analyzed with a biexponential kinetic model using the maximum likelihood estimation (MLE) method. The force-independent kinetic and structural parameters of the underlying bond rupture mechanisms were extracted by fitting the entire data set with a parallel MLE fit procedure using the Zhurkov/Bell model and, alternatively, an Arrhenius kinetics model combined with a Morse potential as an analytic representation of the binding potential. With activation energies between 37 and 40 kJ mol–1, and with Arrhenius prefactors between 5 × 104 and 2 × 106 s–1, the results point to the hydrolysis of the silyl ester bond.
BibTeX:
@article{Schmidt2012,
author = {Schmidt, Sebastian W. and Filippov, Pavel and Kersch, Alfred and Beyer, Martin K. and Clausen-Schaumann, Hauke},
title = {Single-Molecule Force-Clamp Experiments Reveal Kinetics of Mechanically Activated Silyl Ester Hydrolysis},
journal = {ACS Nano},
year = {2012},
volume = {6},
number = {2},
pages = {1314-1321},
doi = {https://doi.org/10.1021/nn204111w}
}
Light Emission Probing Quantum Shot Noise and Charge Fluctuations at a Biased Molecular Junction
N.L. Schneider, J.T. Lu, M. Brandbyge and R. Berndt, Phys. Rev. Lett. 2012, 109, 186601.
Abstract:
The emission of plasmonic light from a single C60 molecule on Cu(111) is probed in a scanning tunneling microscope from the weak-coupling, tunneling range to strong coupling of the molecule to the electrodes at contact. At positive sample voltage the photon yield decreases owing to shot-noise suppression in an increasingly transparent quantum contact. At reversed bias an unexpected nonlinear increase occurs. First-principles transport calculations reveal that ultrafast charge fluctuations on the molecule give rise to additional noise at optical frequencies beyond the shot noise of the current that is injected to the tip.
BibTeX:
@article{Schneider2012,
author = {Schneider, N. L. and Lu, J. T. and Brandbyge, M. and Berndt, R.},
title = {Light Emission Probing Quantum Shot Noise and Charge Fluctuations at a Biased Molecular Junction},
journal = {Phys. Rev. Lett.},
year = {2012},
volume = {109},
pages = {186601},
doi = {https://doi.org/10.1103/PhysRevLett.109.186601}
}
Photochemical dynamics of E-iPr-furylfulgide
J.B. Schonborn, A. Koslowski, W. Thiel and B. Hartke, Phys. Chem. Chem. Phys. 2012, 14, 12193-12201.
Abstract:
As an important theoretical step towards unraveling the mechanistic details of the photochemical switching processes in molecules of the fulgide type, we carried out a large-scale, full-dimensional computational study of the ring closure reaction of E-iPr-furylfulgide. Simulated static UV spectra and femtosecond transient spectra are in good agreement with their experimental counterparts. Using surface-hopping photodynamics simulations, we identify three major de-excitation pathways and their interplay. The dominant photochemical pathway (70% of the trajectories) allows for ring closure, while the two minor pathways involve E-Z double bond isomerization rather than cyclization. The relative abundance of the pathways is rationalized by arguments linking structure with dynamics. It should be emphasized, however, that the distinction into three pathways is only a simplified interpretational model, since the actual dynamical trajectories do not strictly follow these idealized pathways but often show mixed behaviour, evolving along two or three of them during the course of the simulation.
BibTeX:
@article{Schonborn2012,
author = {Schonborn, Jan Boyke and Koslowski, Axel and Thiel, Walter and Hartke, Bernd},
title = {Photochemical dynamics of E-iPr-furylfulgide},
journal = {Phys. Chem. Chem. Phys.},
year = {2012},
volume = {14},
pages = {12193-12201},
doi = {https://doi.org/10.1039/C2CP41817G}
}
Thermodynamic and kinetic stabilization of divanadate in the monovanadate/divanadate equilibrium using a Zn-cyclene derivative: Towards a simple ATP synthase model
H. Sell, A. Gehl, F.D. Sönnichsen and R. Herges, Beilstein J. Org. Chem 2012, 8, 81-89.
Abstract:
For the condensation of anions such as phosphate and ADP to form ATP and water, nature employs sophisticated supramolecular systems to overcome coulomb repulsion and activation barriers. For an attempt to create a simple, analogous chemical system, the dimerization of vanadate is probably the simplest model. We have investigated Zn-benzylcyclene which favors the dimerization thermodynamically as shown by NMR titration. Moreover, EXSY NMR experiments reveal that the vanadate dimer is also kinetically stabilized with respect to hydrolysis by complexation with Zn-cyclene.
BibTeX:
@article{Sell2012,
author = {Sell, Hanno and Gehl, Anika and Sönnichsen, Frank D. and Herges, Rainer},
title = {Thermodynamic and kinetic stabilization of divanadate in the monovanadate/divanadate equilibrium using a Zn-cyclene derivative: Towards a simple ATP synthase model},
journal = {Beilstein J. Org. Chem},
year = {2012},
volume = {8},
pages = {81-89},
doi = {https://doi.org/10.3762/bjoc.8.8}
}
Bis(4-methoxypyridin-3-yl)diazene
S. Thies, C. Näther and R. Herges, Acta Crystallographica Section E 2012, 68, o1568.
Abstract:
The asymmetric unit of the title compound, C12H12N4O2, consists of one half-molecule, which is located on a center of inversion. The molecule has a step-like shape; the azo group adopting a trans configuration, with the pyridine rings being parallel-displace.
BibTeX:
@article{Thies2012,
author = {Thies, Steffen and Näther, Christian and Herges, Rainer},
title = {Bis(4-methoxypyridin-3-yl)diazene},
journal = {Acta Crystallographica Section E},
year = {2012},
volume = {68},
pages = {o1568},
doi = {https://doi.org/10.1107/S1600536812018326}
}
Light-Driven Coordination-Induced Spin-State Switching: Rational Design of Photodissociable Ligands
S. Thies, H. Sell, C. Bornholdt, C. Schütt, F. Köhler, F. Tuczek and R. Herges, Chemistry – A European Journal 2012, 18, 16358-16368.
Abstract:
The bistability of spin states (e.g., spin crossover) in bulk materials is well investigated and understood. We recently extended spin-state switching to isolated molecules at room temperature (light-driven coordination-induced spin-state switching, or LD-CISSS). Whereas bistability and hysteresis in conventional spin-crossover materials are caused by cooperative effects in the crystal lattice, spin switching in LD-CISSS is achieved by reversibly changing the coordination number of a metal complex by means of a photochromic ligand that binds in one configuration but dissociates in the other form. We present mathematical proof that the maximum efficiency in property switching by such a photodissociable ligand (PDL) is only dependent on the ratio of the association constants of both configurations. Rational design by using DFT calculations was applied to develop a photoswitchable ligand with a high switching efficiency. The starting point was a nickel–porphyrin as the transition-metal complex and 3-phenylazopyridine as the photodissociable ligand. Calculations and experiments were performed in two iterative steps to find a substitution pattern at the phenylazopyridine ligand that provided optimum performance. Following this strategy, we synthesized an improved photodissociable ligand that binds to the Ni–porphyrin with an association constant that is 5.36 times higher in its trans form than in the cis form. The switching efficiency between the diamagnetic and paramagnetic state is efficient as well (72 % paramagnetic Ni–porphyrin after irradiation at 365 nm, 32 % paramagnetic species after irradiation at 440 nm). Potential applications arise from the fact that the LD-CISSS approach for the first time allows reversible switching of the magnetic susceptibility of a homogeneous solution. Photoswitchable contrast agents for magnetic resonance imaging and light-controlled magnetic levitation are conceivable applications.
BibTeX:
@article{Thies2012a,
author = {Thies, Steffen and Sell, Hanno and Bornholdt, Claudia and Schütt, Christian and Köhler, Felix and Tuczek, Felix and Herges, Rainer},
title = {Light-Driven Coordination-Induced Spin-State Switching: Rational Design of Photodissociable Ligands},
journal = {Chemistry – A European Journal},
year = {2012},
volume = {18},
pages = {16358-16368},
doi = {https://doi.org/10.1002/chem.201201698}
}
Structures of phthalocyanine molecules on surfaces studied by STM
Y. Wang, K. Wu, J. Kröger and R. Berndt, AIP Advances 2012, 2, 041402.
Abstract:
This review mainly focuses on progress recently achieved in the growth of phthalocyanine molecules on single-crystal surfaces of sub-monolayer up to few-monolayer thin films studied by scanning tunneling microscopy in our groups. On metallic surfaces such as Au(111), Ag(111) and Cu(111), molecular superstructures are determined by combining directional intermolecular interactions caused by symmetry reduction, molecule-substrate interactions and indirect long-range interactions due to quantum interference of surface state electrons. On semiconducting TiO2 surface, molecular assembling structures are dictated by the strong molecule-substrate interaction. However, on insulating NaCl film, molecule-molecule interaction dominates over the molecule-NaCl coupling, leading to molecular growth behavior. Knowledge obtained from these studies would help people better understand the physicochemical properties of the phthalocyanine molecules at surfaces so that their new applications could be further explored and uncovered in the future.
BibTeX:
@article{wang2012,
author = {Yongfeng Wang and Kai Wu and Jörg Kröger and and Richard Berndt},
title = {Structures of phthalocyanine molecules on surfaces studied by STM},
journal = {AIP Advances},
year = {2012},
volume = {2},
pages = {041402},
doi = {https://doi.org/10.1063/1.4773458}
}
Voltage-dependent conductance states of a single-molecule junction
Y.F. Wang, N. Néel, J. Kröger, H. Vázquez, M. Brandbyge, B. Wang and R. Berndt, Journal of Physics: Condensed Matter 2012, 24, 394012.
Abstract:
Ag–Sn-phthalocyanine–Ag junctions are shown to exhibit three conductance states. While the junctions are conductive at low bias, their impedance drastically increases above a critical bias. Two-level fluctuations occur at intermediate bias. These characteristics may be used to protect a nanoscale circuit. Further experiments along with calculations reveal that the self-limiting conductance of the junctions is due to reversible changes of the junction geometry.
BibTeX:
@article{Wang2012,
author = {Y F Wang and N Néel and J Kröger and H Vázquez and M Brandbyge and B Wang and R Berndt},
title = {Voltage-dependent conductance states of a single-molecule junction},
journal = {Journal of Physics: Condensed Matter},
year = {2012},
volume = {24},
pages = {394012},
doi = {https://doi.org/10.1088/0953-8984/24/39/394012}
}
Dual purpose S-trityl-linkers for glycoarray fabrication on both polystyrene and gold
J.W. Wehner, M.J. Weissenborn, M. Hartmann, C.J. Gray, R. Sardzik, C.E. Eyers, S.L. Flitsch and T.K. Lindhorst, Org. Biomol. Chem. 2012, 10, 8919-8926.
Abstract:
There is a wide range of immobilisation reactions to tether substrates to a variety of surfaces for array-based analysis. Most of these immobilisation strategies are specific for a particular surface and require an additional linker to be attached to the substrate or the surface. Furthermore, the analysis of functionalised surfaces is often restricted to certain analytical techniques and therefore, different immobilisation strategies for different surfaces are desirable. Here we have tested an S-tritylated linker for non-covalent or covalent immobilisation of mannosides to polystyrene or gold surfaces. S-Tritylated mannosides with varying linkers were readily synthesised and used to add to biorepulsive maleimide-terminated preformed SAMs after in situ deprotection of the S-trityl group. In addition, S-tritylated mannosides themselves formed stable glycoarrays on polystyrene microtiter plates. The glycoarrays were successfully analysed by MALDI-ToF mass spectrometry, SPR spectroscopy, and interrogated with GFP-transfected Escherichia coli cells. This work has shown that a dual purpose linker can be used on multiple surfaces to form arrays allowing for different testing as well as analytical approaches.
BibTeX:
@article{Wehner2012,
author = {Wehner, Johannes W. and Weissenborn, Martin J. and Hartmann, Mirja and Gray, Christopher J. and Sardzik, Robert and Eyers, Claire E. and Flitsch, Sabine L. and Lindhorst, Thisbe K.},
title = {Dual purpose S-trityl-linkers for glycoarray fabrication on both polystyrene and gold},
journal = {Org. Biomol. Chem.},
year = {2012},
volume = {10},
pages = {8919-8926},
doi = {https://doi.org/10.1039/C2OB26118A}
}
Photoswitchable Azoheterocycles via Coupling of Lithiated Imidazoles with Benzenediazonium Salts
T. Wendler, C. Schütt, C. Näther and R. Herges, The Journal of Organic Chemistry 2012, 77, 3284-3287.
Abstract:
In contrast to azobenzenes, heterocyclic azo compounds are less well investigated. Phenylazoimidazoles would be versatile as photodissociable ligands (PDLs) because imidazole is an important donor in coordination chemistry. Here, we present the synthesis of 4- and 5-phenylazoimidazoles via a novel azo-coupling method. 1,2-Protected imidazole is lithiated in the 5-position and coupled with benzenediazonium tetrafluoroborate. Several new phenylazoimidazoles were prepared. They exhibit an excellent switching behavior. Upon irradiation of the trans isomers with UV light, >95% of the cis forms are obtained. Upon heating, a complete transformation back to the trans configuration was achieved. Back switching with visible light, however, is incomplete.
BibTeX:
@article{Wendler2012,
author = {Wendler, Thore and Schütt, Christian and Näther, Christian and Herges, Rainer},
title = {Photoswitchable Azoheterocycles via Coupling of Lithiated Imidazoles with Benzenediazonium Salts},
journal = {The Journal of Organic Chemistry},
year = {2012},
volume = {77},
number = {7},
pages = {3284-3287},
doi = {https://doi.org/10.1021/jo202688x}
}
Tetrakis(diisopropyl amide) substituted norbornadiene and quadricyclane are highly barium selective ligands
T. Winkler, M. Bayrhuber, B. Sahlmann and R. Herges, Dalton Trans. 2012, 41, 7037-7040.
Abstract:
Tetrakis(diisopropyl amide) substituted norbornadiene and quadricyclane derivatives were investigated for their extraction and transport capabilities with alkaline earth metal cations. Both amides exhibited a remarkably high preference of Ba2+ over any other alkali metal or alkaline earth cation. The binding geometries were determined by quantum chemical DFT calculations.
BibTeX:
@article{Winkler2012,
author = {Winkler, Torsten and Bayrhuber, Monika and Sahlmann, Benjamin and Herges, Rainer},
title = {Tetrakis(diisopropyl amide) substituted norbornadiene and quadricyclane are highly barium selective ligands},
journal = {Dalton Trans.},
year = {2012},
volume = {41},
pages = {7037-7040},
doi = {https://doi.org/10.1039/C2DT30242J}
}
Plasmon-Mediated Embedding of Nanoparticles in a Polymer Matrix: Nanocomposites Patterning, Writing, and Defect Healing
A.U. Zillohu, R. Abdelaziz, M.K. Hedayati, T. Emmler, S. Homaeigohar and M. Elbahri, The Journal of Physical Chemistry C 2012, 116, 17204-17209.
Abstract:
Plasmonics, as an emerging field, aims to exploit the unique optical properties of metallic nanostructures to enable routing and active manipulation of light on the nanoscale. Plasmonic heating is a phenomenon, which is recently recognized for its potential in photothermal therapy. Here we show the first proof-of-concept experiment based on plasmonic heating for selective and precise embedding of nanoparticles in a polymeric matrix. We demonstrate a unique way for in situ fabrication of nanocomposites in different forms including patterning, writing, and defect healing in a controlled manner along with crystallinity control through light irradiation.
BibTeX:
@article{Zillohu2012,
author = {Zillohu, Ahnaf Usman and Abdelaziz, Ramzy and Hedayati, Mehdi Keshavarz and Emmler, Thomas and Homaeigohar, Shahin and Elbahri, Mady},
title = {Plasmon-Mediated Embedding of Nanoparticles in a Polymer Matrix: Nanocomposites Patterning, Writing, and Defect Healing},
journal = {The Journal of Physical Chemistry C},
year = {2012},
volume = {116},
number = {32},
pages = {17204-17209},
doi = {https://doi.org/10.1021/jp3016358}
}
Surface photovoltage effect at the p-WSe2 :Rb surface: Photoemission experiment and numerical model
J. Buck, J. Iwicki, K. Rossnagel and L. Kipp, Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 075312.
Abstract:
It is shown that a combined experimental and theoretical study of the surface photovoltage (SPV) effect can be utilized for the quantification of a number of material parameters in a semiconductor-adsorbate model system. At the Rb-adsorbed surface of the semiconducting layered transition metal dichalcogenide WSe2 , a large SPV effect of ≈600 meV is observed already at a moderate photon flux. Using valence band PES and an auxiliary tunable light source, the surface potential and the SPV effect are traced as a function of the adsorbate density and absorbed light intensity. We find that a major part of the stationary band back bending as a function of photon flux is constrained to a highly sensitive region, that is, a large fraction (50%–80%) of the total SPV magnitude rises within less than 1 order of magnitude. The effect is reproduced by a numerical model involving semiclassical charge carrier dynamics in the surface space charge layer. Among the parameters determined from the simulation, we find an approximate bulk acceptor density between 0.9 × 1017 and 2 × 1017 cm−3 , a broad distribution of adsorbate donor levels at ≈0.2 eV above the conduction band minimum, and electron and hole carrier mobilities μ= 0.7 cm2 /(V s), μ= 1.5 cm2 /(V s) in the crystallographic c direction.
BibTeX:
@article{Buck2011,
author = {Buck, J. and Iwicki, J. and Rossnagel, K. and Kipp, L.},
title = {Surface photovoltage effect at the p-WSe2 :Rb surface: Photoemission experiment and numerical model},
journal = {Phys. Rev. B: Condens. Matter Mater. Phys.},
year = {2011},
volume = {83},
pages = {075312},
doi = {https://doi.org/10.1103/PhysRevB.83.075312}
}
Omnidirectional Transparent Conducting Metal based Plasmonic Nanocomposite
M. Elbahri, M. Keshavarz Hedayati, V.S.K. Chakravadhanula, M. Jamali, T. Strunkus, V. Zaporojtchenko and F. Faupel, Adv. Materials 2011, 23, 1993-1997.
Abstract:
A transparent conducting metal (TCM) composed of a stack of a gold film and silver /polymer nanocomposite fabricated by sputtering onto a glass substrate are presented. Our plasmonic metamaterial shows an omni directional optical transmission up to 80 % in the visible spectrum (see figure), which is comparable to that of ITO, along with electrical conductivity which is one order of magnitude higher.
BibTeX:
@article{Elbahri2011,
author = {Elbahri, Mady and Keshavarz Hedayati, Mehdi and Chakravadhanula, Venkata Sai Kiran and Jamali, Mohammad and Strunkus, Thomas and Zaporojtchenko, Vladimir and Faupel, Franz},
title = {Omnidirectional Transparent Conducting Metal based Plasmonic Nanocomposite},
journal = {Adv. Materials},
year = {2011},
volume = {23},
pages = {1993-1997},
doi = {https://doi.org/10.1002/adma.201003811}
}
Visualizing the invisible nanoworld: ICT-enhanced reflection of imaging and images of atoms in nanoscience
M. Euler, in: Education in a Technological World: Communicating Current and Emerging Research and Technological Efforts. 2011, 599-606.
Abstract:
New tools for visualizing and manipulating systems down to the level of individual atoms play a decisive role in the advancement of nanoscience and assign a prominent role to images as a means of communication. However, making nanoworld imagery tangible to students or to the public is a challenge, because photo-realistic views interfere with adequate conceptual interpretations. The article focuses on scanning tunneling microscopy (STM). In order to develop a critical epistemology towards STM images, an acoustic analogy is presented using sound waves as probes to map arrays of acoustical resonators. Starting from hands-on experiments, ICT-tools are used to create an augmented reality that transforms sound fields into visual representations. The acoustic near field imaging is fully transparent and classical-quantum analogies establish a correspondence with tunneling spectroscopy. A thorough reflection of the imaging process helps to counteract naive misinterpretations of nano-visualizations. Moreover, the acoustic model stimulates new insights by elucidating the power of near field scanning microscopy to resolve structures much smaller than the wavelength.
BibTeX:
@inbook{Euler2011,
author = {Euler, Manfred},
title = {Visualizing the invisible nanoworld: ICT-enhanced reflection of imaging and images of atoms in nanoscience},
booktitle = {Education in a Technological World: Communicating Current and Emerging Research and Technological Efforts},
publisher = {Formatex Research Center, Badajoz, Spain},
year = {2011},
pages = {599-606},
url = {http://www.formatex.info/ict/book/599-606.pdf}
}
Coverage-Driven Electronic Decoupling of Fe-Phthalocyanine from a Ag(111) Substrate
T.G. Gopakumar, T. Brumme, J. Kröger, C. Toher, G. Cuniberti and R. Berndt, J. Phys. Chem. C 2011, 115, 12173-12179.
Abstract:
Coverage-dependent structural and electronic properties of Fe-phthalocyanine (FePc) molecules adsorbed on Ag(111) have been investigated by scanning tunneling microscopy/spectroscopy and density functional calculations. While spectra of single FePc molecules are dominated by a broad signature of Fe d orbitals, spectra of molecules in an ordered superstructure resolve spectroscopic contributions from individual dz2 and dxz/dyz orbitals. Calculations suggest that an increased molecule surface distance in the superstructure and a change of the Ag(111) surface electronic structure cause the spectral changes, which are consistent with a partial electronic decoupling of the molecules from the substrate. A progressive evolution toward a gap around the Fermi level is observed for molecules on the first and second molecular layer.
BibTeX:
@article{Gopakumar2011,
author = {Gopakumar, T. G. and Brumme, T. and Kröger, J. and Toher, C. and Cuniberti, G. and Berndt, R.},
title = {Coverage-Driven Electronic Decoupling of Fe-Phthalocyanine from a Ag(111) Substrate},
journal = {J. Phys. Chem. C},
year = {2011},
volume = {115},
pages = {12173-12179},
doi = {https://doi.org/10.1021/jp2038619}
}
Free volume changes upon optical switching in azobenzene-PMMA blends studied by a pulsed low-energy positron beam
S. Harms, K. Rätzke, C. Pakula, V. Zaporojtchenko, T. Strunskus, W. Egger, P. Sperr and F. Faupel, Journal of Polymer Science 2011, 49, 404-408.
Abstract:
Polymers including chromophores, which can be switched by light, have been studied extensively during the last years due to a host of potential applications which arise from the marked changes in physical properties on switching. Even though there is clear evidence that the free volume has a significant influence on the isomerization kinetics, the question of free volume changes on switching was only addressed recently. Using a pulsed low-energy positron beam the ortho-positronium lifetime τ3 was taken as a very sensitive free volume probe, and no change in free volume was detected on isomerization in an azobenzene-polymethylmethacrylate (PMMA) copolymer containing about 8 wt % of the azobenzene moiety. Here, we report for the first time on free volume changes in an azobenzene-PMMA blend with an azobenzene moiety concentration as high as 40 wt %. Using the same pulsed low-energy positron beam, small but significant changes of τ3 were observed between the structurally relaxed dark and the UV-illuminated states suggesting a decrease in free volume of the order of 10%.
BibTeX:
@article{Harms2011,
author = {Harms, S. and Rätzke, K. and Pakula, C. and Zaporojtchenko, V. and Strunskus, T. and Egger, W. and Sperr, P. and Faupel, F.},
title = {Free volume changes upon optical switching in azobenzene-PMMA blends studied by a pulsed low-energy positron beam},
journal = {Journal of Polymer Science},
year = {2011},
volume = {49},
pages = {404-408},
doi = {https://doi.org/10.1002/polb.22201}
}
Design of a Perfect Black Absorber at Visible Frequencies Using Plasmonic Metamaterials
M.K. Hedayati, M. Javaherirahim, B. Mozooni, R. Abdelaziz, A. Tavassolizadeh, V.S.K. Chakravadhanula, V. Zaporojtchenko, T. Strunkus, F. Faupel and M. Elbahri, Advanced Materials 2011, 23, 5410-5414.
Abstract:
The design and fabrication of a plasmonic black absorber with almost 100% absorbance spanning a broad range of frequencies from ultraviolet (UV) to the near infrared (NIR) is demonstrated. The perfect plasmonic absorber is achieved by a combination of a metal film with suitable metal/dielectric nanocomposites. Our fabrication technique is simple, versatile, cost-effective, and compatible with current industrial methods for solar absorber production.
BibTeX:
@article{Hedayati2011,
author = {Hedayati, Mehdi Keshavarz and Javaherirahim, Mojtaba and Mozooni, Babak and Abdelaziz, Ramzy and Tavassolizadeh, Ali and Chakravadhanula, Venkata Sai Kiran and Zaporojtchenko, Vladimir and Strunkus, Thomas and Faupel, Franz and Elbahri, Mady},
title = {Design of a Perfect Black Absorber at Visible Frequencies Using Plasmonic Metamaterials},
journal = {Advanced Materials},
year = {2011},
volume = {23},
number = {45},
pages = {5410-5414},
doi = {https://doi.org/10.1002/adma.201102646}
}
Two-Photon Photoemission from Ex-situ Prepared Butanethiol SAMs on Au(111)
N. Heinemann, T. Leissner, J. Grunau, T. Rohwer, O. Andreev and M. Bauer, Chemical Physics 2011, 382, 1-4.
Abstract:
Self-assembled monolayers (SAMs) of butanethiol on a Au(111) single crystalline surface in the p × 3 lying-down phase prepared by deposition from solution were studied with two-photon photoemission (2PPE) spectroscopy. The spectra reveal clear signatures of two unoccupied resonance states at energies E − EF = 3.7 eV and 3.9 eV. The low-energy state is assigned to the characteristic σ∗ -resonance associated with the Au-S bond of the thiolate. The energy of the other resonance state agrees well with an interface state reported before for different alkanethiol SAMs on Au(111) in a standing-up phase. Furthermore the 2PPE data provide indications that the high quality of the ex-situ prepared SAMs support the formation of image potential states.
BibTeX:
@article{Heinemann2011,
author = {Heinemann, N. and Leissner, T. and Grunau, J. and Rohwer, T. and Andreev, O. and Bauer, M.},
title = {Two-Photon Photoemission from Ex-situ Prepared Butanethiol SAMs on Au(111)},
journal = {Chemical Physics},
year = {2011},
volume = {382},
pages = {1-4},
doi = {https://doi.org/10.1016/j.chemphys.2011.03.002}
}
Spinschaltung und intelligente Kontrastmittel in der MRT
R. Herges, Nachrichten aus der Chemie 2011, 59, 817-821.
Abstract:
Isolierte Atome und Moleküle existieren in zwei magnetischen Zuständen: dia- und para magnetisch. Bis vor kurzem war magnetische Bistabilität auf Festkörper beschränkt und Einzelmoleküle ließen sich bei Raumtemperatur nicht zwischen diesen Zuständen hin und her schalten. Die Entwicklung des ligandgetriebenen Spinwechsels erlaubt nun auch das Spinschalten ohne kooperative Effekte. Neue Anwendungen wie schaltbare Kontrastmittel für die Kernspintomographie sind so möglich.
BibTeX:
@article{Herges2011,
author = {Herges, Rainer},
title = {Spinschaltung und intelligente Kontrastmittel in der MRT},
journal = {Nachrichten aus der Chemie},
year = {2011},
volume = {59},
number = {9},
pages = {817-821},
doi = {https://doi.org/10.1002/nadc.201190013}
}
Photoresponsive Transparent Conductive Metal with a Photobleaching Nose
M. Jamali, M. Keshavarz Hedayati, B. Mozooni, M. Javaherirahim, R. Abdelaziz, A. Usman Zillohu and M. Elbahri, Adv. Materials 2011, 23, 4243-4247.
Abstract:
A photoswitchable, transparent, and highly conducting device that functions via nanophotonic interaction of a metal film coated with spirophenanthrooxazine (SPO) molecules embedded in a polymeric matrix and fabricated through spin coating is demonstrated. The device possesses additional novel functionality as a photobleaching gas sensor.
BibTeX:
@article{Jamali2011,
author = {Jamali, Mohammad and Keshavarz Hedayati, Mehdi and Mozooni, Babak and Javaherirahim, Mojtaba and Abdelaziz, Ramzy and Usman Zillohu, Ahnaf and Elbahri, Mady},
title = {Photoresponsive Transparent Conductive Metal with a Photobleaching Nose},
journal = {Adv. Materials},
year = {2011},
volume = {23},
pages = {4243-4247},
doi = {https://doi.org/10.1002/adma.201102353}
}
Azobenzene-Containing Triazatriangulenium Adlayers on Au(111): Structural and Spectroscopic Characterization.
U. Jung, S. Kuhn, U. Cornelissen, F. Tuczek, T. Strunskus, V. Zaporojtchenko, J. Kubitschke, R. Herges and O. Magnussen, Langmuir 2011, 27, 5899-5908.
Abstract:
Adlayers of different azobenzene-functionalized derivs. of the triazatriangulenium (TATA) platform on Au(111) surfaces were studied by scanning tunneling microscopy (STM), x-ray photoelectron scpectroscopy (XPS), gap-mode surface-enhanced Raman spectroscopy (gap-mode SERS), and cyclic voltammetry (CV). The chem. compn. of the adlayers is in good agreement with the mol. structure, i.e., different chem. groups attached to the azobenzene functionality were identified. Also, the presence of the azobenzene moieties in the adlayers was verified by the vibration spectra and electrochem. data. The mols. remain intact upon adsorption with the freestanding functional groups oriented perpendicularly to the TATA platform and thus also to the substrate surface.
BibTeX:
@article{Jung2011,
author = {Jung, Ulrich and Kuhn, Sonja and Cornelissen, Ursula and Tuczek, Felix and Strunskus, Thomas and Zaporojtchenko, Vladimir and Kubitschke, Jens and Herges, Rainer and Magnussen, Olaf.},
title = {Azobenzene-Containing Triazatriangulenium Adlayers on Au(111): Structural and Spectroscopic Characterization.},
journal = {Langmuir},
year = {2011},
volume = {27},
pages = {5899-5908},
doi = {https://doi.org/10.1021/la104654p}
}
Adlayers based on molecular platforms of trioxatriangulenium.
S. Kuhn, U. Jung, S. Ulrich, R. Herges and O. Magnussen, Chem. Commun. 2011, 47, 8880-8882.
Abstract:
The platform approach for prepn. of mol. adlayers with freestanding functional groups was extended to systems from the trioxatriangulenium ion. Self-assembled monolayers of these compds. were prepd. on Au(111) surfaces and characterized by scanning tunneling microscopy, revealing highly-ordered structures.
BibTeX:
@article{Kuhn2011,
author = {Kuhn, Sonja and Jung, Ulrich and Ulrich, Sandra and Herges, Rainer and Magnussen, Olaf.},
title = {Adlayers based on molecular platforms of trioxatriangulenium.},
journal = {Chem. Commun.},
year = {2011},
volume = {47},
pages = {8880-8882},
doi = {https://doi.org/10.1039/C1CC12598B}
}
Morphological and magnetic properties of TiO2 / Fe50Co50 composite films
A. Kulkarni, V. Chakravadhanula, V. Duppel, D. Meyners, V. Zaporojtchenko, T. Strunskus, L. Kienle, E. Quandt and F. Faupel, Journal of Materials Science 2011, 46, 4638-4645.
Abstract:
Nanocomposites of FeCo and TiO2 with wide range of metal volume fractions (MVF) were prepared by co-sputtering. High resolution transmission electron microscopy analysis reveals that the microstructure of the nanocomposites depends on the MVF which determines the particle size and separation. FeCo nanoparticles are amorphous at lower MVF whereas crystallites are present at higher MVF. Likewise, the magnetic characteristics of these films depend on the MVF. At low MVF, composite films exhibit superparamagnetism whereas at high MVF, coalescence of crystalline nanoparticles results in the opening up of hysteresis loop. These composite films show a considerable room temperature tunnel magnetoresistance and being proportional to the square of the normalized magnetization (M/Ms)2.
BibTeX:
@article{Kulkarni2011,
author = {Kulkarni, A. and Chakravadhanula, V.S.K. and Duppel, V. and Meyners, D. and Zaporojtchenko, V. and Strunskus, T. and Kienle, L. and Quandt, E. and Faupel, F.},
title = {Morphological and magnetic properties of TiO2 / Fe50Co50 composite films},
journal = {Journal of Materials Science},
year = {2011},
volume = {46},
pages = {4638-4645},
doi = {https://doi.org/10.1007/s10853-011-5366-2}
}
Electronic decoupling of a cyclophane from a metal surface
F. Matino, G. Schull, F. Köhler, S. Gabutti, M. Mayor and R. Berndt, Proc. Natl. Acad. Sci. 2011, 108, 961-964.
Abstract:
Electronic self-decoupling of an organic chromophore from a metal substrate is achieved using a naphtalenediimide cyclophane to spatially separate one chromophore unit of the cyclophane from the substrate. Observations of vibronic excitations in scanning tunneling spectra demonstrate the success of this approach. These excitations contribute a significant part of the tunneling current and give rise to clear structure in scanning tunneling microscope images. We suggest that this approach may be extended to implement molecular functions at metal surfaces.
BibTeX:
@article{Matino2010a,
author = {Matino, F. and Schull, G. and Köhler, F. and Gabutti, S. and Mayor, M. and Berndt, R.},
title = {Electronic decoupling of a cyclophane from a metal surface},
journal = {Proc. Natl. Acad. Sci.},
year = {2011},
volume = {108},
pages = {961-964},
doi = {https://doi.org/10.1073/pnas.1006661107}
}
The First Porous MOF with Photoswitchable Linker Molecules
A. Modrow, D. Zargarani, R. Herges and N. Stock, J. Chem. Soc. Dalton Trans. 2011, 40, 4217-4222.
Abstract:
We synthesized a porous twofold interpenetrated MOF [Zn2(NDC)2(1)] (coined CAU-5) using 3-azo-phenyl-4,4′-bipyridine (1), 2,6-naphthalenedicarboxylic acid, and Zn(NO3)2·6H2O. The azo-functionality protrudes into the pores, and can be switched, by irradiation with UV light (365 nm), from the thermodynamically stable trans-isomer to the cis-isomer. Back-switching was achieved thermally and with an irradiation wavelength of λmax = 440 nm.
BibTeX:
@article{Modrow2011,
author = {Modrow, Antje and Zargarani, Dordaneh and Herges, Rainer and Stock, Norbert},
title = {The First Porous MOF with Photoswitchable Linker Molecules},
journal = {J. Chem. Soc. Dalton Trans.},
year = {2011},
volume = {40},
pages = {4217-4222},
doi = {https://doi.org/10.1039/C0DT01629B}
}
In situ atomic force microscopy studies of reversible light-induced switching of surface roughness and adhesion in azobenzene-containing PMMA films.
M. Mueller, Y. Gonzalez-Garcia, C. Pakula, V. Zaporojtchenko, T. Strunskus, F. Faupel, R. Herges, D. Zargarani and O.M. Magnussen, Appl. Surf. Sci. 2011, 257, 7719-7726.
Abstract:
Thin films in the range 40-80 nm of a blend of PMMA with an azobenzene deriv. were studied directly during UV and blue light irradn. by at. force microscopy (AFM), revealing highly reversible changes in the surface roughness and the film adhesion. UV light induces an ≈80% increase in surface roughness, whereas illumination by blue light completely reverses these changes. Based on the obsd. surface topog. and transition kinetics a reversible mass flow mechanisms is suggested, where the polarity changes upon switching trigger a wetting-dewetting transition in a surface segregation layer of the chromophore. Similar AFM measurements of the pull-off force indicate a decrease upon UV and an increase after blue light illumination with a complex kinetic behavior: a rapid initial change, attributed to the change in the cis isomer fraction of the azobenzene deriv., and a more gradual change, indicative of slow structural reorganization.
BibTeX:
@article{Mueller2011,
author = {Mueller, M. and Gonzalez-Garcia, Y. and Pakula, C. and Zaporojtchenko, V. and Strunskus, T. and Faupel, F. and Herges, R. and Zargarani, D. and Magnussen, O. M.},
title = {In situ atomic force microscopy studies of reversible light-induced switching of surface roughness and adhesion in azobenzene-containing PMMA films.},
journal = {Appl. Surf. Sci.},
year = {2011},
volume = {257},
pages = {7719-7726},
doi = {https://doi.org/10.1016/j.apsusc.2011.04.016}
}
First observation of light-induced spin change in vacuum deposited thin films of iron spin crossover complexes
H. Naggert, A. Bannwarth, S. Chemnitz, H. van Hofe, E. Quandt and F. Tuczek, J. Chem. Soc. Dalton Trans. 2011, 40, 6364.
Abstract:
Thin films of [Fe(H2Bpz)2(phen)] (1) and [Fe(H2Bpz)2(bipy)] (2) are prepared by vacuum deposition and investigated with respect to their spin crossover behaviour. For the first time light-induced excited spin state trapping (LIESST) is observed in such systems. T1/2 and TLIESST in the films are in agreement with the bulk values.
BibTeX:
@article{Naggert2011,
author = {Naggert, Holger and Bannwarth, Alexander and Chemnitz, S. and van Hofe, H. and Quandt, Eckhard and Tuczek, Felix},
title = {First observation of light-induced spin change in vacuum deposited thin films of iron spin crossover complexes},
journal = {J. Chem. Soc. Dalton Trans.},
year = {2011},
volume = {40},
pages = {6364},
doi = {https://doi.org/10.1039/C1DT10651A}
}
Two-Level Conductance Fluctuations of a Single-Molecule Junction
N. Neel, J. Kroger and R. Berndt, Nano Lett. 2011, 11, 3593-3596.
Abstract:
The conductance of a single-molecule junction in a lowtemperature scanning tunneling microscope has been measured at nanosecond time resolution. In a transition region between tunneling and contact the conductance exhibits rapid two-level fluctuations which are attributed to different geometries of the junction. The voltage dependence of the fluctuations indicates that electrons injected into the lowest unoccupied molecular orbital may efficiently couple to molecular vibrations.
BibTeX:
@article{Neel2011,
author = {Neel, N. and Kroger, J. and Berndt, R.},
title = {Two-Level Conductance Fluctuations of a Single-Molecule Junction},
journal = {Nano Lett.},
year = {2011},
volume = {11},
pages = {3593-3596},
doi = {https://doi.org/10.1021/nl201327c}
}
Optical switching behavior of azobenzene/PMMA blends with high chromophore concentration
C. Pakula, C. Hanisch, V. Zaporojtchenko, T. Strunskus, C. Bornholdt, D. Zargarani, R. Herges and F. Faupel, J. Mater. Sci. 2011, 46, 2488-2494.
Abstract:
In this article, the authors will present a simple way to produce thin solid organic films, with a content of more than 60 wt% photoactive molecules dispersed in a polymeric matrix showing an almost complete and fully reversible photoisomerization. These high filling factors could be achieved by using branched side chains in the molecules, which prevent crystallization. The chromophores were codissolved with the polymer Polymethylmethacrylate (PMMA) of different Mw in toluene in various concentrations and spin casted onto the substrate. The effect of the Mw of PMMA on the switching kinetics and the agglomeration tendency of different molecule configurations were investigated.
BibTeX:
@article{Pakula2010a,
author = {Pakula, Christina and Hanisch, Christian and Zaporojtchenko, Vladimir and Strunskus, Thomas and Bornholdt, Claudia and Zargarani, Dordaneh and Herges, Rainer and Faupel, Franz},
title = {Optical switching behavior of azobenzene/PMMA blends with high chromophore concentration},
journal = {J. Mater. Sci.},
year = {2011},
volume = {46},
pages = {2488-2494},
doi = {https://doi.org/10.1007/s10853-010-5097-9}
}
Mechanically activated rupture of single covalent bonds: evidence of force induced bond hydrolysis
S.W. Schmidt, A. Kersch, M.K. Beyer and H. Clausen-Schaumann, Phys. Chem. Chem. Phys. 2011, 13, 5994-5999.
Abstract:
We have used temperature-dependent single molecule force spectroscopy to stretch covalently anchored carboxymethylated amylose (CMA) polymers attached to an amino-functionalized AFM cantilever. Using an Arrhenius kinetics model based on a Morse potential as a one-dimensional representation of covalent bonds, we have extracted kinetic and structural parameters of the bond rupture process. With 35.5 kJ mol−1, we found a significantly smaller dissociation energy and with 9.0 × 102 s−1 to 3.6 × 103 s−1 also smaller Arrhenius pre-factors than expected for homolytic bond scission. One possible explanation for the severely reduced dissociation energy and Arrhenius pre-factors is the mechanically activated hydrolysis of covalent bonds. Both the carboxylic acid amide and the siloxane bond in the amino-silane surface linker are in principle prone to bond hydrolysis. Scattering, slope and curvature of the scattered data plots indicate that in fact two competing rupture mechanisms are observed.
BibTeX:
@article{Schmidt2011,
author = {Schmidt, Sebastian W. and Kersch, Alfred and Beyer, Martin K. and Clausen-Schaumann, Hauke},
title = {Mechanically activated rupture of single covalent bonds: evidence of force induced bond hydrolysis},
journal = {Phys. Chem. Chem. Phys.},
year = {2011},
volume = {13},
pages = {5994-5999},
doi = {https://doi.org/10.1039/C0CP02827D}
}
Light emission from a double-decker molecule on a metal surface
N.L. Schneider, F. Matino, g. Schull, s. Gabutti, m. Mayor and r. Berndt, Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 84, 153403.
Abstract:
A scanning tunneling microscope is used to induce the emission of light from a monolayer of naphtalenediimide cyclophane, a molecule comprising two separate π-electron systems. Spectra of the emission exhibit clear features related to vibrational molecular states. They are interpreted in terms of the unusual density of unoccupied states of the molecule, which causes a drastic preference of inelastic tunneling to the molecular affinity level.
BibTeX:
@article{Schneider2011,
author = {Schneider, N. L. and Matino, F. and Schull, g. and Gabutti, s. and Mayor, m. and Berndt, r.},
title = {Light emission from a double-decker molecule on a metal surface},
journal = {Phys. Rev. B: Condens. Matter Mater. Phys.},
year = {2011},
volume = {84},
pages = {153403},
doi = {https://doi.org/10.1103/PhysRevB.84.153403}
}
Charge Injection through Single and Double Carbon Bonds
G. Schull, Y.J. Dappe, C. Gonzalez, H. Bulou and R. Berndt, Nano Lett. 2011, 11, 3142-3146.
Abstract:
The contact conductance of oriented C60 molecules is probed with a scanning tunneling microscope as a function of the lateral position of the tip in contact to the molecular cage. Together with first principles calculations, these measurements reveal variations of the efficiency of charge injection to the fullerene molecule with the order of the contacted carbon–carbon bond.
BibTeX:
@article{Schull2011,
author = {Schull, Guillaume and Dappe, Yannick J. and Gonzalez, Cesar and Bulou, Herve and Berndt, Richard},
title = {Charge Injection through Single and Double Carbon Bonds},
journal = {Nano Lett.},
year = {2011},
volume = {11},
pages = {3142-3146},
doi = {https://doi.org/10.1021/nl201185y}
}
Atomic-scale engineering of electrodes for single-molecule contacts
G. Schull, T. Frederiksen, A. Arnau, D. Sánchez-Portal and R. Berndt, Nature Nanotechnology 2011, 6, 23-27.
Abstract:
The transport of charge through a conducting material depends on the intrinsic ability of the material to conduct current and on the charge injection efficiency at the contacts between the conductor and the electrodes carrying current to and from the material1, 2, 3. According to theoretical considerations4, this concept remains valid down to the limit of single-molecule junctions5. Exploring this limit in experiments requires atomic-scale control of the junction geometry. Here we present a method for probing the current through a single C60 molecule while changing, one by one, the number of atoms in the electrode that are in contact with the molecule. We show quantitatively that the contact geometry has a strong influence on the conductance. We also find a crossover from a regime in which the conductance is limited by charge injection at the contact to a regime in which the conductance is limited by scattering at the molecule. Thus, the concepts of ‘good’ and ‘bad’ contacts, commonly used in macro- and mesoscopic physics, can also be applied at the molecular scale.
BibTeX:
@article{Schull2010,
author = {Schull, Guillaume and Frederiksen, Thomas and Arnau, Andrés and Sánchez-Portal, Daniel and Berndt, Richard},
title = {Atomic-scale engineering of electrodes for single-molecule contacts},
journal = {Nature Nanotechnology},
year = {2011},
volume = {6},
pages = {23-27},
doi = {https://doi.org/10.1038/nnano.2010.215}
}
Photodimerisation of glycothymidines in solution and in micelles
K. Schwekendiek, H. Kobarg, L. Daumlechner, F.D. Sonnichsen and T.K. Lindhorst, Chem. Commun. 2011, 47, 9399-9401.
Abstract:
Glycothymidines were designed and synthesized as a new class of functional glycomimetics in which a photochemical [2+2] cycloaddition of the thymine moiety induces structural changes of carbohydrate presentation. To test if photodimerisation of these glycothymidines is feasible within an array of molecules, the photochemical reaction was investigated using NMR and NMR diffusion experiments in solution as well as in the supramolecular context of detergent micelles that mimic cellular membranes.
BibTeX:
@article{Schwekendiek2011,
author = {Schwekendiek, Kirsten and Kobarg, Hauke and Daumlechner, Lena and Sonnichsen, Frank D. and Lindhorst, Thisbe K.},
title = {Photodimerisation of glycothymidines in solution and in micelles},
journal = {Chem. Commun.},
year = {2011},
volume = {47},
pages = {9399-9401},
doi = {https://doi.org/10.1039/C1CC13246F}
}
Superior Z→E and E→Z photoswitching dynamics of dihydrodibenzodiazocine, a bridged azobenzene, by S1(nπ*) excitation at λ = 387 and 490 nm
R. Siewertsen, J.B. Schönborn, B. Hartke, F. Renth and F. Temps, Phys. Chem. Chem. Phys. 2011, 13, 1054-1063.
Abstract:
The ultrafast Z → E and E → Z photoisomerisation dynamics of 5,6-dihydrodibenzo[c,g][1,2]diazocine (1), the parent compound of a class of bridged azobenzene-based photochromic molecular switches with a severely constrained eight-membered heterocyclic ring as central unit, have been studied by femtosecond time-resolved spectroscopy in n-hexane as solvent and by quantum chemical calculations. The diazocine contrasts with azobenzene (AB) in that its Z rather than E isomer is the energetically more stable form. Moreover, it stands out compared to AB for the spectrally well separated S1(nπ*) absorption bands of its two isomers. The Z isomer absorbs at around λ = 404 nm, the E form has its absorption maximum around λ = 490 nm. The observed transient spectra following S1(nπ*) photoexcitation show ultrafast excited-state decays with time constants τ1 = 70 fs for the Z and <50 fs for the E isomer reflecting very fast departures of the excited wave packets from the S1 Franck–Condon regions and τ2 = 270 fs (320 fs) related to the Z → E (resp. E → Z) isomerisations. Slower transient absorption changes on the time scale of τ3 = 5 ps are due to vibrational cooling of the reaction products. The results show that the unique steric constraints in the diazocine do not hinder, but accelerate the molecular isomerisation dynamics and increase the photoswitching efficiencies, contrary to chemical intuition. The observed isomerisation times and quantum yields are rationalised on the basis of CASPT2//CASSCF calculations by a S1/S0 conical intersection seam at a CNNC dihedral angle of ≈96° involving twisting and torsion of the central CNNC moiety. With improved photochromism, high quantum yields, short reaction times and good photostability, diazocine 1 and its derivatives constitute outstanding candidates for photoswitchable molecular tweezers and other applications.
BibTeX:
@article{Siewertsen2011a,
author = {Siewertsen, Ron and Schönborn, Jan Boyke and Hartke, Bernd and Renth, Falk and Temps, Friedrich},
title = {Superior Z→E and E→Z photoswitching dynamics of dihydrodibenzodiazocine, a bridged azobenzene, by S1(nπ*) excitation at λ = 387 and 490 nm},
journal = {Phys. Chem. Chem. Phys.},
year = {2011},
volume = {13},
pages = {1054-1063},
doi = {https://doi.org/10.1039/C0CP01148G}
}
Tuning of switching properties and excited-state dynamics of fulgides by structural modifications
R. Siewertsen, F. Strübe, J. Mattay, F. Renth and F. Temps, Phys. Chem. Chem. Phys. 2011, 13, 3800-3808.
Abstract:
The ultrafast photo-induced dynamics of the E-isomers of four selected photochromic fulgides with distinct structural motifs have been elucidated by femtosecond broadband transient absorption spectroscopy in n-hexane as solvent. E → C and E → Z isomerisations, respectively, with time constants of [similar]0.12 ± 0.02 ps and [similar]0.34 ± 0.03 ps taking place in parallel were found for derivatives with a methyl substituent at the central hexatriene (HT) unit. In contrast, fulgides with increased steric constraints by an iso-propyl substituent or by intramolecular bridging displayed virtually zero E → Z isomerisation, but instead a desired accelerated and more efficient ring closure in a reaction time of only [similar]50 ± 10 fs. Both photoisomerisations appear to follow excited-state pathways with distinctive conical intersections. For the ring closure, direct barrierless pathways with steep downhill gradients are likely. Furthermore, the results indicate conformer-specific reactions, with ring closure exclusively by the Eα conformer and E → Z isomerisation predominantly by the Eβ conformer, because the Eα → Z channel is unfavoured by the faster and kinetically more competitive Eα → C reaction. DFT calculations of the equilibrium structures showed that the sterically demanding groups at the HT unit shift the conformer equilibria towards the Eα conformers. At the same time, they appear to cause a favourable pre-orientation of the furyl unit that accelerates the conrotatory ring closure in the Eα → C reaction. Benzo-annulation of the furyl unit has little effect on the observed dynamics. Overall, the results demonstrate how the excited-state dynamics and thereby the photoswitching properties of fulgides can be successfully tuned and improved by structural modifications at the chromophores.
BibTeX:
@article{Siewertsen2011,
author = {Siewertsen, R. and Strübe, F. and Mattay, J. and Renth, F. and Temps, F.},
title = {Tuning of switching properties and excited-state dynamics of fulgides by structural modifications},
journal = {Phys. Chem. Chem. Phys.},
year = {2011},
volume = {13},
pages = {3800-3808},
doi = {https://doi.org/10.1039/C0PC01890B}
}
Electronic and steric effects on the photo-induced C - E ring-opening of structurally modified furylfulgides
R. Siewertsen, F. Strübe, J. Mattay, F. Renth and F. Temps, Phys. Chem. Chem. Phys. 2011, 13, 15699-15707.
Abstract:
The ultrafast C - E ring-opening reactions of four selectively modified furylfulgides have been studied by means of ultrafast broadband transient absorption spectroscopy after femtosecond laser excitation at l = 500 nm. A large difference in the dynamics was found in the case of benzannulation at the furyl moiety as an example for an electronic effect by extension of the conjugated p-electron system compared to furylfulgides carrying sterically different alkyl substituents at the central cyclohexadiene (CHD) ring. The measured very similar spectro-temporal absorption maps for the furylfulgides with a methyl or isopropyl group at the CHD ring or an intramolecular alkyl bridge from the CHD to the furyl moiety showed two distinctive excited-state absorptions with slightly different decay times. The first time constant (t1 = 0.39–0.57 ps) was assigned to the rapid departure of the excited wavepacket from the Franck–Condon region. The slightly longer second decay time of t2 = 0.66–0.92 ps, depending on the compound, was attributed to the electronic deactivation and ring-opening through a conical intersection to the S0 state. In contrast, the benzannulation at the furyl moiety was found to lead to a bi-phasic excited-state decay with t2 = 4.7 ps and a much slower additional contribution of t3 = 17.4 ps, E25 times longer compared to the normal furylfulgides. The drastic change is attributed to a trapping of excited molecules in a local potential energy minimum en route to the conical intersection.
BibTeX:
@article{Siewertsen2011b,
author = {Siewertsen, Ron and Strübe, Frank and Mattay, Jochen and Renth, Falk and Temps, Friedrich},
title = {Electronic and steric effects on the photo-induced C - E ring-opening of structurally modified furylfulgides},
journal = {Phys. Chem. Chem. Phys.},
year = {2011},
volume = {13},
pages = {15699-15707},
doi = {https://doi.org/10.1039/c1cp21320b}
}
Controlled Metalation of a Single Adsorbed Phthalocyanine
A. Sperl, J. Kröger and R. Berndt, Angew. Chem. 2011, 123, 5406-5409.
highlighted in Nature Chemistry
Abstract:
The controlled metalation of individual phthalocyanine (H2Pc) molecules to form AgPc was observed by low-temperature scanning tunneling microscopy (STM). Stepwise dehydrogenation was followed by Ag+ implantation; tautomerization and hydrogen atom hopping within the H2Pc inner ring were also induced by electron injection from the STM tip.
BibTeX:
@article{Sperl2011a,
author = {Sperl, Alexander and Kröger, Jörg and Berndt, Richard},
title = {Controlled Metalation of a Single Adsorbed Phthalocyanine},
journal = {Angew. Chem.},
year = {2011},
volume = {123},
pages = {5406-5409},
note = {highlighted in Nature Chemistry},
doi = {https://doi.org/10.1002/ange.201100950}
}
Demetalation of a Single Organometallic Complex
A. Sperl, J. Kröger and R. Berndt, J. Am. Chem. Soc. 2011, 133, 11007-11009.
Abstract:
Single lead-phthalocyanine molecules adsorbed to ultrathin lead islands on Ag(111) are demetalized by transferring the lead atom of the inner macrocycle to the tip of a scanning tunneling microscope. Reactants and products are discriminated by their images and spectroscopic fingerprints.
BibTeX:
@article{Sperl2011b,
author = {Sperl, Alexander and Kröger, Jörg and Berndt, Richard},
title = {Demetalation of a Single Organometallic Complex},
journal = {J. Am. Chem. Soc.},
year = {2011},
volume = {133},
pages = {11007-11009},
doi = {https://doi.org/10.1021/ja203199q}
}
Electronic Superstructure of Lead Phthalocyanine on Lead Islands
A. Sperl, J. Kröger and R.B. Berndt, J. Phys. Chem. A 2011, 115, 6973-6978.
Abstract:
Lead phthalocyanine (PbPc) deposited on lead islands on Ag(111) forms two-dimensional crystals of densely packed molecules. For particular orientations, the molecular arrays exhibit an electronic superstructure with an extraordinarily large unit cell. The molecules induce a shift of quantum well states, which are confined to the Pb islands. Patterns formed by PbPc on Ag(111) are drastically different.
BibTeX:
@article{Sperl2011,
author = {Sperl, A. and Kröger, Jörg and Berndt, Richard Berndt},
title = {Electronic Superstructure of Lead Phthalocyanine on Lead Islands},
journal = {J. Phys. Chem. A},
year = {2011},
volume = {115},
pages = {6973-6978},
doi = {https://doi.org/10.1021/jp112169s}
}
Photochromism of Rotation-Hindered Furylfulgides Influenced by Steric Modifications
F. Strübe, R. Siewertsen, F.D. Sönnichsen, F. Renth, F. Temps and J. Mattay, Eur. J. Org. Chem. 2011, 1947-1955.
Abstract:
The syntheses of a bicyclic furylfulgide 14 and a (benzofuryl)fulgide 15 with increased steric constraints are described. Their photochromic behaviors were analyzed by means of UV/Vis spectroscopic measurements, X-ray crystallography, and NMR experiments, and the results were compared to those of the furyl(methyl)fulgide 12 and the furyl(isopropyl)fulgide 13. Compounds 13E and 14E exhibit large quantum yields of 0.57 and 0.53 for the coloration reaction (E) → (C) compared with 12E and 15E (0.23 and 0.17). After irradiation with 350 nm light, 13E and 14E are transformed into the closed (C) forms almost quantitatively, whereas 12E and 15E result in a photostationary state with mixtures of the (E), (Z), and (C) forms. The crystal structures obtained for 13E, 14E, and 15E show that the fulgides adopt cyclizable helical (P)-Eα conformations with no significant differences in atomic distances in the hexatriene unit. 2D- and temperature-dependent NMR experiments showed that the enantio- and diastereotopomerization processes were suppressed in a fulgide for the first time. Compound 14E populates only the Eα conformational state. In contrast, 13E and 15E both exist in the cyclizable Eα and the non-cyclizable Eβ conformations in solution. Due to the annulated benzene ring, 15E exhibits a higher thermodynamic barrier than 13E, so the “belly roll” process was reduced for 15, but the (E) → (Z) isomerization could not be suppressed. The structural modification of 14 successfully suppressed the (E) → (Z) isomerization as well as the belly roll process. The way in which the isomerization reaction is suppressed by steric hindrance could not be fully elucidated by using these methods.
BibTeX:
@article{Struebe2011,
author = {Strübe, Frank and Siewertsen, Ron and Sönnichsen, Frank D. and Renth, Falk and Temps, Friedrich and Mattay, Jochen},
title = {Photochromism of Rotation-Hindered Furylfulgides Influenced by Steric Modifications},
journal = {Eur. J. Org. Chem.},
year = {2011},
pages = {1947-1955},
doi = {https://doi.org/10.1002/ejoc.201001649}
}
5-Chloro-2-(phenyldiazenyl)pyridine
S. Thies, C. Näther and R. Herges, Acta Crystallographica Section E 2011, 67, o3298.
Abstract:
In the title compound, C11H8ClN3, the azo group adopts a trans conformation and the dihedral angle between the six-membered rings is 15.47 (8)°.
BibTeX:
@article{Thies2011a,
author = {Thies, Steffen and Näther, Christian and Herges, Rainer},
title = {5-Chloro-2-(phenyldiazenyl)pyridine},
journal = {Acta Crystallographica Section E},
year = {2011},
volume = {67},
pages = {o3298},
doi = {https://doi.org/10.1107/S1600536811047556}
}
Light-induced Spin-Change by Photodissociable External Ligands: A New Principle for Magnetic Switching of Molecules.
S. Thies, H. Sell, C. Schuett, C. Bornholdt, C. Naether, F. Tuczek and R. Herges, J. Am. Chem. Soc. 2011, 133, 16243-16250.
Abstract:
Magnetic bistability in spin crossover materials generally is a collective phenomenon which arises from the cooperative interaction of a large no. of microscopic magnetic moments within the crystal lattice in the solid state. We now report on individual mols. in homogeneous soln. that are switched between the dia- and paramagnetic state at room temp. by light driven coordination induced spin state switching (LD-CISSS). Switching of the coordination no. (and concurrently of the spin state) is achieved by using Ni-porphyrin as a square planar platform, and azopyridines as photodissociable axial ligands. The square planar Ni-porphyrin is diamagnetic (low spin, S=0), and all complexes with axial ligands are paramagnetic (high spin, S=1). Assocn. consts. are detd. for all conceivable 1:1 and 1:2 porphyrin/azopyridine complexes. The binding consts. of the trans azopyridines are larger than those of the corresponding cis isomers. Thus, upon irradn. with UV light (365 nm, trans → cis), and visible light (455 nm, cis → trans) switching of magnetic properties is achieved. Upon substitution of the azopyridines in 4,4'-position with larger substituents the difference in trans and cis assocn. consts., and thus the switching efficiency is increased. A photoinduced switching between 20 and 68 % paramagnetic Ni species in soln. is achieved with iso-Pr substituents at room temp.
BibTeX:
@article{Thies2011,
author = {Thies, Steffen and Sell, Hanno and Schuett, Christian and Bornholdt, Claudia and Naether, Christian and Tuczek, Felix and Herges, Rainer.},
title = {Light-induced Spin-Change by Photodissociable External Ligands: A New Principle for Magnetic Switching of Molecules.},
journal = {J. Am. Chem. Soc.},
year = {2011},
volume = {133},
pages = {16243-16250},
doi = {https://doi.org/10.1021/ja206812f}
}
Magnetic Bistability of Molecules in Homogeneous Solution at Room Temperature
S. Venkataramani, U. Jana, M. Dommaschk, F.D. Sönnichsen, F. Tuczek and R. Herges, Science 2011, 331, 445-448.
Abstract:
Magnetic bistability, as manifested in the magnetization of ferromagnetic materials or spin crossover in transition metal complexes, has essentially been restricted to either bulk materials or to very low temperatures. We now present a molecular spin switch that is bistable at room temperature in homogeneous solution. Irradiation of a carefully designed nickel complex with blue-green light (500 nanometers) induces coordination of a tethered pyridine ligand and concomitant electronic rearrangement from a diamagnetic to a paramagnetic state in up to 75% of the ensemble. The process is fully reversible on irradiation with violet-blue light (435 nanometers). No fatigue or degradation is observed after several thousand cycles at room temperature under air. Preliminary data show promise for applications in magnetic resonance imaging.
BibTeX:
@article{Venkataramani2011,
author = {Venkataramani, Sugumar and Jana, Umasish and Dommaschk, Marcel and Sönnichsen, Frank D. and Tuczek, Felix and Herges, Rainer},
title = {Magnetic Bistability of Molecules in Homogeneous Solution at Room Temperature},
journal = {Science},
year = {2011},
volume = {331},
pages = {445-448},
doi = {https://doi.org/10.1126/science.1201180}
}
Reversible light-induced capacitance switching of azobenzene ether/PMMA blends
V. Zaporojtchenko, C. Pakula, S. Wahyuni Basuki, T. Strunskus, D. Zargarani, R. Herges and F. Faupel, Appl. Phys. A 2011, 102, 421-427.
Abstract:
Fully reversible light-induced switching of the capacitance with changes larger than 50% has been achieved by using photo-active thin polymer films. The films consist of PMMA polymer blended with high concentrations of branched azobenzene ether dye molecules. Polymer thin sheet capacitors can be easily produced by spin coating and drop casting in various thicknesses ranging from 100 nm to 8 µm, respectively. Reversible capacitance switching is induced by illumination with UV and visible light, respectively. The capacitance change is correlated to the trans to cis isomerization of the azobenzene ether molecules and the alignment of the molecular dipoles in the film. Switching times depend on chromophore concentration, film thickness and light intensity used. The influence of wavelength of the light, of the temperature as well as of an electrical field applied during illumination on the capacitance change is addressed.
BibTeX:
@article{Zaporojtchenko2011,
author = {Zaporojtchenko, Vladimir and Pakula, Christina and Wahyuni Basuki, Sri and Strunskus, Thomas and Zargarani, Dordaneh and Herges, Rainer and Faupel, Franz},
title = {Reversible light-induced capacitance switching of azobenzene ether/PMMA blends},
journal = {Appl. Phys. A},
year = {2011},
volume = {102},
pages = {421-427},
doi = {https://doi.org/10.1007/s00339-010-6139-5}
}
Spatiotemporal control of nano-optical excitations
M. Aeschlimann, M. Bauer, D. Bayer, T. Brixner, S. Cunovic, F. Dimler, A. Fischer, W. Pfeiffer, M. Rohmer, C. Schneider, F. Steeb, C. Strüber and D.V. Voronine, Proceedings of the National Acedemy of Science 2010, 107, 5329-5333.
Abstract:
The most general investigation and exploitation of light-induced processes require simultaneous control over spatial and temporal properties of the electro-magnetic field on a femtosecond time- and nanometer length-scale. Based on the combination of polarization pulse shaping and time-resolved two-photon photoemission electron microscopy we demonstrate such control over nanoscale spatial and ultrafast temporal degrees of freedom of an electromagnetic excitation in the vicinity of a nanostructure. The time-resolved cross-correlation measurement of the local photoemission yield reveals the switching of the nano-localized optical near-field distribution with a lateral resolution well below the diffraction limit and a temporal resolution on the femtosecond time scale. In addition, successful adaptive spatio-temporal control demonstrates the flexibility of the method. This flexible simultaneous control of temporal and spatial properties of nanophotonic excitations opens new possibilities to tailor and optimize the light-mater interaction in spectroscopic methods as well as in nanophotonic applications.
BibTeX:
@article{Aeschlimann2010,
author = {Aeschlimann, Martin and Bauer, Michael and Bayer, Daniela and Brixner, Tobias and Cunovic, Stefan and Dimler, Frank and Fischer, Alexander and Pfeiffer, Walter and Rohmer, Martin and Schneider, Christian and Steeb, Felix and Strüber, Christian and Voronine, Dmitri V.},
title = {Spatiotemporal control of nano-optical excitations},
journal = {Proceedings of the National Acedemy of Science},
year = {2010},
volume = {107},
pages = {5329-5333},
doi = {https://doi.org/10.1073/pnas.0913556107}
}
Artificial single variant martensite in freestanding Fe70Pd30 films obtained by coherent epitaxial growth
C. Bechtold, J. Buschbeck, A. Lotnyk, B. Erkartal, S. Hamann, C. Zamponi, L. Schultz, A. Ludwig, L. Kienle, S. Fähler and E. Quandt, Adv. Materials 2010, 22, 1-4.
Abstract:
The mechanically soft behavior of the magnetic shape-memory material Fe70Pd30 allows huge tetragonal distortions to be stabilized in sputtered thin films by coherent epitaxial growth on various metallic buffers. Furthermore, it is demonstrated that epitaxial films more than 1 µm thick can be grown, which makes possible freestanding films in an artificial single variant state suitable for microactuators and sensors.
BibTeX:
@article{Bechtold2010,
author = {Bechtold, C. and Buschbeck, J. and Lotnyk, A. and Erkartal, B. and Hamann, S. and Zamponi, C. and Schultz, L. and Ludwig, A. and Kienle, L. and Fähler, S. and Quandt, Eckhard},
title = {Artificial single variant martensite in freestanding Fe70Pd30 films obtained by coherent epitaxial growth},
journal = {Adv. Materials},
year = {2010},
volume = {22},
pages = {1-4},
doi = {https://doi.org/10.1002/adma.201000599}
}
Controlled single atom and single molecule contacts
R. Berndt, J. Kröger, N. Néel and G. Schull, Phys. Chem. Chem. Phys. 2010, 12, 1022-1032.
Abstract:
The scanning tunnelling microscope (STM) may be used to prepare contacts to single atoms or molecules on surfaces and to investigate the transport of electrons through these junctions. The imaging capabilities of STM along with spectroscopic modes of measurement enable a rather detailed characterisation of the geometric and electronic properties of the contacts. This perspective presents recent investigations into the quantum transport through magnetic atoms and C60 molecules.
BibTeX:
@article{Berndt2010,
author = {Berndt, Richard and Kröger, Jörg and Néel, Nicolas and Schull, Guillaume},
title = {Controlled single atom and single molecule contacts},
journal = {Phys. Chem. Chem. Phys.},
year = {2010},
volume = {12},
pages = {1022-1032},
doi = {https://doi.org/10.1039/b908672m}
}
Preparation and plasmonic properties of polymer-based composites containing Ag-Au alloy nanoparticles produced by vapor phase co-deposition
H.T. Beyene, V.S.K. Chakravadhanula, C. Hanisch, M. Elbahri, T. Strunskus, V. Zaporojtchenko, L. Kienle and F. Faupel, Journal of Materials Science 2010, 45, 5865-5871.
Abstract:
Nanocomposite (NC) thin films with noble metal nanoparticles (NPs) embedded in a dielectric material show very attractive plasmonic properties due to dielectric and quantum confinement effects. For single component NPs, the plasmon resonance frequency can only be tuned in a narrow range. Much interest aroused in bimetallic NPs, however, many wet chemical approaches often lead to core shell particles, which exhibit multiple plasmon resonances or do not allow large variation of the NPs alloy composition and filling factor. Here, we report a vapor phase co-deposition method to produce polymer-metal NCs with embedded homogeneous Ag-Au alloy particles showing a single plasmon resonance. The method allows production of NPs with controlled alloy composition (x), metal filling (f), and nanostructure in a protecting Teflon AF matrix. The nanostructure size and shape were characterized by transmission electron microscope. Energy dispersive X-ray spectroscopy was used to determine x and f. The optical properties and the position of surface plasmon resonance were studied by UV-Vis spectroscopy. The plasmon resonance can be tuned over a large range of the visible spectrum associated with the change in x, f, and nanostructure. Changes upon annealing at 200 °C are also reported.
BibTeX:
@article{Beyene2010,
author = {Beyene, H. T. and Chakravadhanula, V. S. K. and Hanisch, C. and Elbahri, M. and Strunskus, T. and Zaporojtchenko, V. and Kienle, L. and Faupel, Franz},
title = {Preparation and plasmonic properties of polymer-based composites containing Ag-Au alloy nanoparticles produced by vapor phase co-deposition},
journal = {Journal of Materials Science},
year = {2010},
volume = {45},
pages = {5865-5871},
doi = {https://doi.org/10.1007/s10853-010-4663-5}
}
Design of optimally switchable molecules by genetic algorithms
N. Carstensen, J.M. Dieterich and B. Hartke, Phys. Chem. Chem. Phys. 2010, 12, 2903-2910.
Abstract:
We demonstrate the possibility to design molecules for specific tasks, using a fully automatic global optimization setup employing genetic algorithms. As an example, we tune the two excitation wavelengths of a molecular switch backbone to arbitrarily pre-set values, by an automatic optimization of the substituent pattern.
BibTeX:
@article{Carstensen2010a,
author = {Carstensen, N.O. and Dieterich, J. M. and Hartke, Bernd},
title = {Design of optimally switchable molecules by genetic algorithms},
journal = {Phys. Chem. Chem. Phys.},
year = {2010},
volume = {12},
pages = {2903-2910},
doi = {https://doi.org/10.1039/C0CP01065K}
}
Unusual photochemical dynamics of a bridged azobenzene derivative
O. Carstensen, J. Sielk, J.B. Schönborn, C. Granucci and B. Hartke, J.Chem.Phys. 2010, 124305.
Abstract:
In a large-scale simulation study of ultrafast photochemical dynamics for an azobenzene compound with an additional ethylenic bridge we have found unexpected features: While the dynamics starting from the Z isomer follow a barrierless path with steep gradients, the dynamics starting from the E isomer proceed through a different conical intersection surrounded by a rather flat potential energy landscape and then encounter a sizeable barrier in the electronic ground state that markedly influences the reaction behavior. Direct comparisons with experimental static UV spectra, quantum yields and transient absorption spectra show good agreement and reveal signatures of this unusual behavior.
BibTeX:
@article{Carstensen2010,
author = {Carstensen, O. and Sielk, J. and Schönborn, Jan Boyke and Granucci, C. and Hartke, Bernd},
title = {Unusual photochemical dynamics of a bridged azobenzene derivative},
journal = {J.Chem.Phys.},
year = {2010},
pages = {124305},
doi = {https://doi.org/10.1063/1.3479397}
}
CoPc adsorption on Cu(111): Origin of the C4 to C2 symmetry reduction.
R. Cuadrado, J.I. Cerdá, Y. Wang, G. Xin, R. Berndt and H. Tang, J. Chem. Phys. 2010, 133, 154701.
Abstract:
The adsorption of phthalocyanines (Pc) to various surfaces has recently been reported to lead to a lowering of symmetry from C4 to C2 in scanning tunneling microscope (STM) images. Possible origins of the reduced symmetry involve the electronic structure or geometric deformation of the molecules. Here, the origin of the reduction is clarified from a comprehensive theoretical study of CoPc adsorbed on the Cu(111) surface along with the experimental STM data. Total energy calculations using different schemes for the exchange-correlation energy and STM simulations are compared against experimental data. We find that the symmetry reduction is only reproduced when van der Waals corrections are included into the formalism. It is caused by a deformation along the two perpendicular molecular axes, one of them coming closer to the surface by around 0.2 Å. An electronic structure analysis reveals (i) the relevance of the CoPc interaction with the Cu(111) surface state and (ii) that intramolecular features in dI/dV maps clearly discriminate a Co-derived state from the rest of the Pc states.
BibTeX:
@article{Cuadrado2010,
author = {Cuadrado, R. and Cerdá, J. I. and Wang, Y. and Xin, G. and Berndt, R. and Tang, H.},
title = {CoPc adsorption on Cu(111): Origin of the C4 to C2 symmetry reduction.},
journal = {J. Chem. Phys.},
year = {2010},
volume = {133},
pages = {154701},
doi = {https://doi.org/10.1063/1.3502682}
}
Metal-Polymer Nanocomposites for Functional Applications
F. Faupel, V. Zaporojtchenko, T. Strunskus and M. Elbahri, Advanced Engineering Materials 2010, 12, 1177-1190.
Abstract:
Nanocomposites combine favorable features of the constituents on the nanoscale to obtain new functionalities. The present paper is concerned with the preparation of polymer-based nanocomposites consisting of metal nanoparticles in a polymer matrix and the resulting functional properties. Emphasis is placed on vapor phase deposition which inter alia allows the incorporation of alloy clusters with well defined composition and tailored filling factor profiles. Examples discussed here include optical composites with tuned particle surface plasmon resonances for plasmonic applications, magnetic high frequency materials with cut-off frequencies well above 1 GHz, sensors that are based on the dramatic change in the electronic properties near the percolation threshold, and antibacterial coatings which benefit from the large effective surface of nanoparticles and the increased chemical potential which both strongly enhance ion release.
BibTeX:
@article{Faupel2010,
author = {Faupel, Franz and Zaporojtchenko, Vladimir and Strunskus, T. and Elbahri, M.},
title = {Metal-Polymer Nanocomposites for Functional Applications},
journal = {Advanced Engineering Materials},
year = {2010},
volume = {12},
pages = {1177-1190},
doi = {https://doi.org/10.1002/adem.201000231}
}
Synthesis and properties of di- and trinitrobenzyl substituted pyridine derivates.
A. Frej, C. Goeschen, C. Näther, U. Lüning and R. Herges, J. Phys. Org. Chem. 2010, 23, 1093-1098.
Abstract:
A new method to obtain di- and trinitrobenzyl substituted pyridines is presented. By systematic variation of reaction parameters the reaction conditions were optimized. The novel synthesis circumvents the commonly used nitration of benzyl pyridines, and thus avoids the nitration of the heterocycle which is a common side reaction. Furthermore, the starting materials for the synthesis of a variety of photochromic nitrobenzyl pyridines are easily accessible. The halflifes of the phototautomers of several new di- and trinitrobenzyl-substituted pyridines were determined.
BibTeX:
@article{Frej2010,
author = {Adrian Frej and Catrin Goeschen and Christian Näther and Ulrich Lüning and Rainer Herges},
title = {Synthesis and properties of di- and trinitrobenzyl substituted pyridine derivates.},
journal = {J. Phys. Org. Chem.},
year = {2010},
volume = {23},
pages = {1093-1098},
doi = {https://doi.org/10.1002/poc.1781}
}
Coverage Driven Formation of Homochiral Domains of an Achiral Molecule on Au(111)
T.G. Gopakumar, F. Matino, B. Schwager, A. Bannwarth, F. Tuczek, J. Kroger and R. Berndt, J. Phys. Chem. C 2010, 114, 18247-18251.
Abstract:
Adsorption of achiral Ni-tetramethyl-tetraazaannulene on Au(111) leads to the assembly of chiral trimers, which serve as building blocks for larger chiral patterns. A racemic mixture is observed at low coverages. Beyond a critical coverage, extraordinarily large homochiral domains occur and cover entire substrate terraces. The chiral structures and the formation of homochiral domains are induced by steric interactions.
BibTeX:
@article{Gopakumar2010,
author = {Gopakumar, Thiruvancheril G. and Matino, Francesca and Schwager, Bettina and Bannwarth, Alexander and Tuczek, Felix and Kroger, Jorg and Berndt, Richard},
title = {Coverage Driven Formation of Homochiral Domains of an Achiral Molecule on Au(111)},
journal = {J. Phys. Chem. C},
year = {2010},
volume = {114},
pages = {18247-18251},
doi = {https://doi.org/10.1021/jp106973p}
}
Fast electrical response to volatile organic compounds of 2D Au nanoparticle layers embedded into polymers
C. Hanisch, N. Ni, A. Kulkarni, V. Zaporojtchenko, T. Strunskus and F. Faupel, Journal of Materials Science 2010, 46, 438-445.
Abstract:
The conductivity of polymer–metal nanocomposites close to the percolation threshold is very sensitive to changes in the metal nanoparticle distances. Here the technical feasibility of a novel type of easy to prepare polymer–metal nanocomposite sensor is explored, which shall be able to detect a unique signal for various volatile organic compounds (VOCs) exhibiting a fast and reversible response. The composite consists of a nearly 2-dimensional Au nanoparticle layer near the percolation threshold thermally embedded into a thermoplastic polymer film. The sensoric response is based on the swelling behavior of the polymeric matrix upon exposure to the organic vapor molecules. Different from conventional nanocomposite sensors that require long-range diffusion of the volatile compound into the bulk of the matrix, the electrical response here only requires the penetration of the VOC a few nanometer below the surface thus causing a rapid detection. The degree of swelling depends on the type of polymer and VOC used as well as on the vapor pressure of the VOC leading to a characteristic response of each polymer to a specific VOC. This enables a “fingerprint” detection of different VOCs by an array of different polymer nanocomposite combined into one sensoric device.
BibTeX:
@article{Hanisch2010,
author = {Hanisch, C. and Ni, N. and Kulkarni, A. and Zaporojtchenko, Vladimir and Strunskus, T. and Faupel, Franz},
title = {Fast electrical response to volatile organic compounds of 2D Au nanoparticle layers embedded into polymers},
journal = {Journal of Materials Science},
year = {2010},
volume = {46},
pages = {438-445},
doi = {https://doi.org/10.1007/s10853-010-4887-4}
}
Photoswitching of azobenzene multilayers on a layered semiconductor
J. Iwicki, E. Ludwig, M. Kalläne, J. Buck, F. Köhler, R. Herges, L. Kipp and K. Roßnagel, Applied Physics Letters 2010, 97, 063112.
Abstract:
In situ photoelectron spectroscopy is used to study the adsorption and photoisomerization of azobenzene multilayers on the layered semiconductor HfS2 at liquid nitrogen temperatures. The measured valence band spectra indicate weak molecule–substrate coupling and provide evidence for reversible switching of azobenzene multilayers by light with different wavelengths. The photoswitching manifests itself in spectral shifts due to changes in the electrical surface conductance and in modifications of the electronic structure consistent with the results of outer valence Green’s function calculations. The photoemission results appear to establish azobenzene as an optoelectrical molecular switch.
BibTeX:
@article{Iwicki2010,
author = {Iwicki, Jaroslaw and Ludwig, E. and Kalläne, M. and Buck, J. and Köhler, Felix and Herges, Rainer and Kipp, Lutz and Roßnagel, Kai},
title = {Photoswitching of azobenzene multilayers on a layered semiconductor},
journal = {Applied Physics Letters},
year = {2010},
volume = {97},
pages = {063112},
doi = {https://doi.org/10.1063/1.3479502}
}
Photoswitching Behavior of Azobenzene-Containing Alkanethiol Self-Assembled Monolayers on Au Surfaces
U. Jung, O. Filinova, S. Kuhn, D. Zargarani, C. Bornholdt, R. Herges and O. Magnussen, Langmuir 2010, 26, 13913-13923.
Abstract:
The photoisomerization of self-assembled monolayers of azobenzene-containing alkanethiols, as well as of mixed monolayers of these substances with n-alkanethiol spacer molecules on Au surfaces, was studied by photoelectrochemical measurements and surface plasmon resonance spectroscopy. A strong dependence on the molecular structure of the adsorbates was found, specifically on the linker between the azobenzene moiety and the alkanethiol: while molecules with an amide group were photoinactive, those with an ether group exhibited pronounced, reversible photoisomerization in pure and mixed adlayers. Both trans−cis and cis−trans isomerization followed first-order kinetics with time constants that suggest high quantum efficiencies for these processes.
BibTeX:
@article{Jung2010,
author = {Jung, Ulrich and Filinova, Olena and Kuhn, Sonja and Zargarani, Dordaneh and Bornholdt, Claudia and Herges, Rainer and Magnussen, Olaf},
title = {Photoswitching Behavior of Azobenzene-Containing Alkanethiol Self-Assembled Monolayers on Au Surfaces},
journal = {Langmuir},
year = {2010},
volume = {26},
pages = {13913-13923},
doi = {https://doi.org/10.1021/la1015109}
}
Gap-mode SERS studies of azobenzene-containing self-assembled monolayers on Au(111).
U. Jung, M. Mueller, N. Fujimoto, K. Ikeda, K. Uosaki, U. Cornelissen, F. Tuczek, C. Bornholdt, D. Zargarani, R. Herges and O. Magnussen, J. Colloid Interface Sci. 2010, 341, 366-375.
Abstract:
Self-assembled monolayers of azobenzene-contg. thiols on smooth Au(1 1 1) surfaces were studied by gap-mode surface-enhanced Raman spectroscopy (gap-mode SERS). By adsorption of colloidal Au nanoparticles on top of the org. adlayer highly reproducible spectra with strongly enhanced intensities are obtained. The obsd. bands indicate a trans conformation of the azobenzene moieties and are in agreement with structural data for the mol. layer. A characteristic dependency on the terminal and the spacer groups of the mols. is found. Samples prepd. during illumination with UV light show pronounced spectral differences that can be attributed to azobenzene in cis conformation. [on SciFinder(R)]
BibTeX:
@article{Jung2009,
author = {Jung, Ulrich and Mueller, Mathias and Fujimoto, Norihiro and Ikeda, Katsuyoshi and Uosaki, Kohei and Cornelissen, Ursula and Tuczek, Felix and Bornholdt, Claudia and Zargarani, Dordaneh and Herges, Rainer and Magnussen, Olaf},
title = {Gap-mode SERS studies of azobenzene-containing self-assembled monolayers on Au(111).},
journal = {J. Colloid Interface Sci.},
year = {2010},
volume = {341},
pages = {366-375},
doi = {https://doi.org/10.1016/j.jcis.2009.09.040}
}
Synthesis of Functionalized Triazatriangulenes for Application in Photo-switchable Self-assembled Monolayers
J. Kubitschke, C. Näther and R. Herges, Eur. J. Org. Chem. 2010, 5041-5055.
Abstract:
Various triazatriangulenes are synthesized by nucleophilic attack at the central C atom of triazatriangulenium ions. The molecular functions, especially azobenzenes, are fixed via an ethynyl linker by in situ deprotection of trimethylsilyl alkynes. The structure of two of these molecules is further investigated by X-ray crystallography. The photo-induced trans/cis-isomerization of the azobenzene substituted derivatives is analyzed in solution and shows great promise for the preparation of switchable functionalized monolayers, as the triazatriangulenes are known for their self-assembly on gold surfaces.
BibTeX:
@article{Kubitschke2010,
author = {Kubitschke, Jens and Näther, Christian and Herges, Rainer},
title = {Synthesis of Functionalized Triazatriangulenes for Application in Photo-switchable Self-assembled Monolayers},
journal = {Eur. J. Org. Chem.},
year = {2010},
pages = {5041-5055},
doi = {https://doi.org/10.1002/ejoc.201000650}
}
Self-assembly of triazatriangulenium-based functional adlayers on Au(111) surfaces
S. Kuhn, B. Baisch, U. Jung, T. Johannsen, J. Kubitschke, R. Herges and O. Magnussen, Phys. Chem. Chem. Phys. 2010, 12, 4481-4487.
Abstract:
Detailed scanning tunneling microscopy studies of the attachment of freestanding molecular functions to Au(111) surfaces via self-assembly of functional molecules based on triazatriangulenium platforms are presented. As shown for molecules with side chains of different length and phenyl, azobenzyl, or azobenzyl derivatives with different terminal groups (iodo, cyano, or dimethyl) as functional units, this approach allows the preparation of very stable, hexagonally ordered adlayers. The intermolecular spacings in these adlayers are independent of the attached functions with the latter being orientated perpendicular to the Au surface. Due to their open structure, adlayers of platforms with attached functional groups exhibit a tendency towards bilayer formation, which can be suppressed by derivatization with appropriate terminal groups.
BibTeX:
@article{Kuhn2010,
author = {Kuhn, Sonja and Baisch, Belinda and Jung, Ulrich and Johannsen, Torben and Kubitschke, Jens and Herges, Rainer and Magnussen, Olaf},
title = {Self-assembly of triazatriangulenium-based functional adlayers on Au(111) surfaces},
journal = {Phys. Chem. Chem. Phys.},
year = {2010},
volume = {12},
pages = {4481-4487},
doi = {https://doi.org/10.1039/b922882a}
}
27- to 39-Membered Pyridine Macrocycles
U. Lüning, E. Mak, M. Zindler, B. Hartkopf and R. Herges, Eur. J. Org. Chem. 2010, 4932-4940.
Abstract:
Abstract: A set of 27- to 39-membered pyridine macrocycles 2 and 3 has been synthesized by Williamson ether synthesis or ring closing metathesis. The pyridines are 2,6-disubstituted to allow endo-interactions. In addition to the length, also the nature of an aliphatic chain has been varied: saturated (2) and unsaturated (3).
BibTeX:
@article{Luening2010,
author = {Lüning, Ulrich and Mak, Ellen and Zindler, Melanie and Hartkopf, Britta and Herges, Rainer},
title = {27- to 39-Membered Pyridine Macrocycles},
journal = {Eur. J. Org. Chem.},
year = {2010},
pages = {4932-4940},
doi = {https://doi.org/10.1002/ejoc.201000505}
}
Single azopyridine-substituted porphyrin molecules for configurational and electronic switching
F. Matino, G. Schull, U. Jana, F. Köhler, R. Berndt and R. Herges, Chem. Comm. 2010, 6780-6782.
Abstract:
A new azopyridine functionalized Ni–porphyrin was synthesized as a model compound for deposition and switch on surfaces. Two geometrically and electronically different states of single molecules on Au(111) were found by scanning tunneling microscopy/spectroscopy and analyzed with density functional calculations.
BibTeX:
@article{Matino2010,
author = {Matino, Francesca and Schull, Guillaume and Jana, Umasish and Köhler, Felix and Berndt, Richard and Herges, Rainer},
title = {Single azopyridine-substituted porphyrin molecules for configurational and electronic switching},
journal = {Chem. Comm.},
year = {2010},
pages = {6780-6782},
doi = {https://doi.org/10.1039/C0CC00959H}
}
Reversible light-controlled conductance switching of azobenzene based metal/polymer nanocomposites
C. Pakula, V. Zaporojtchenko, T. Strunskus, D. Zargarani, R. Herges and F. Faupel, Nanotechnology 2010, 21, 465201.
Abstract:
We present a new concept of light-controlled conductance switching based on metal/polymer nanocomposites with dissolved chromophores that do not have intrinsic current switching ability. Photoswitchable metal/PMMA nanocomposites were prepared by physical vapor deposition of Au and Pt clusters, respectively, onto spin-coated thin poly(methylmethacrylate) films doped with azo-dye molecules. High dye concentrations were achieved by functionalizing the azo groups with tails and branches, thus enhancing solubility. The composites show completely reversible optical switching of the absorption bands upon alternating irradiation with UV and blue light. We also demonstrate reversible light-controlled conductance switching. This is attributed to changes in the metal cluster separation upon isomerization based on model experiments where analogous conductance changes were induced by swelling of the composite films in organic vapors and by tensile stress.
BibTeX:
@article{Pakula2010,
author = {Pakula, C. and Zaporojtchenko, V. and Strunskus, T. and Zargarani, D. and Herges, R. and Faupel, F.},
title = {Reversible light-controlled conductance switching of azobenzene based metal/polymer nanocomposites},
journal = {Nanotechnology},
year = {2010},
volume = {21},
pages = {465201},
doi = {https://doi.org/10.1088/0957-4484/21/46/465201}
}
Self-Assembled Monolayers of Benzylmercaptan and p-Cyanobenzylmercaptan on Gold: Surface Infrared Spectroscopic Characterization
K. Rajalingam, L. Hallmann, T. Strunskus, A. Bashir, C. Wöll and F. Tuczek, Phys. Chem. Chem. Phys. 2010, 12, 4390 - 4399.
Abstract:
Self-assembled monolayers (SAMs) on gold substrates were prepared from benzylmercaptan (BM) and para-cyanobenzylmercaptan (pCBM), and the resulting surfaces were investigated using conventional infrared reflection-absorption spectroscopy (IRRAS) as well as polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). IRRAS data are analyzed by comparison with transmission IR spectra and theoretical (DFT) simulations. The spectroscopic results indicate the presence of well-ordered monolayers of BM and pCBM with an orientation perpendicular to the surface. IRRAS and PM-IRRAS data are compared to each other and the respective merits of both methods are discussed.
BibTeX:
@article{Rajalingam2010,
author = {Rajalingam, K. and Hallmann, L. and Strunskus, T. and Bashir, A. and Wöll, C. and Tuczek, F.},
title = {Self-Assembled Monolayers of Benzylmercaptan and p-Cyanobenzylmercaptan on Gold: Surface Infrared Spectroscopic Characterization},
journal = {Phys. Chem. Chem. Phys.},
year = {2010},
volume = {12},
pages = {4390 - 4399},
doi = {https://doi.org/10.1039/b923628g}
}
Pump-Probe Spectroscopy of Ultrafast Vibronic Dynamics in Organic Chromophores
F. Renth, N.K. Schwalb, R. Siewertsen and F. Temps, in Conical Intersections II, Domcke, W. and Köppel, H. and Yarkony, D. (Eds.), World Scientific 2010, in press.
BibTeX:
@article{Renth2010,
author = {Renth, Falk and Schwalb, Nina K. and Siewertsen, Ron and Temps, Friedrich},
title = {Pump-Probe Spectroscopy of Ultrafast Vibronic Dynamics in Organic Chromophores},
journal = {in Conical Intersections II, Domcke, W. and Köppel, H. and Yarkony, D. (Eds.), World Scientific},
year = {2010},
pages = {in press}
}
Simple Coupling Chemistry Linking Carboxyl-Containing Organic Molecules to Silicon Oxide Surfaces under Acidic Conditions
S.W. Schmidt, T. Christ, C. Glockner, M.K. Beyer and H. Clausen-Schaumann, Langmuir 2010, 26, 15333-15338.
Abstract:
The coupling chemistry of carboxymethylated amylose with organo-silanized silicon oxide surfaces at pH 7.4 and 2.0 was investigated using atomic force microscopy (AFM) based single-molecule force spectroscopy. At close to neutral pH, carbodiimide activation of a carboxylic acid affords formation of an amide bond with an amino surface linker. At pH 2.0, no activation with carbodiimide was required to anchor carboxymethylated amylose between an AFM tip and a glass substrate. At the same time, the mean bond rupture force fr dropped from 1.65 ± 0.37 nN at pH 7.4 to 1.39 ± 0.30 nN at pH 2.0 without carbodiimide, indicating that a different link to the surface can be formed at low pH. The coupling mechanism at pH 2.0 was elucidated by a series of experiments, in which the surface was functionalized with four different organosilanes, each containing characteristic functional groups. The results are rationalized with an acid-catalyzed ester condensation between a carboxyl group and a free, unreacted silanol group in the surface anchor or on the surface.
BibTeX:
@article{Schmidt2010,
author = {Schmidt, Sebastian W. and Christ, Timo and Glockner, Christian and Beyer, Martin K. and Clausen-Schaumann, Hauke},
title = {Simple Coupling Chemistry Linking Carboxyl-Containing Organic Molecules to Silicon Oxide Surfaces under Acidic Conditions},
journal = {Langmuir},
year = {2010},
volume = {26},
pages = {15333-15338},
doi = {https://doi.org/10.1021/la102435f}
}
Photochemical ring opening of cyclohexadiene: Quantum wavepacket dynamics on a global ab initio potential energy surface
J.B. Schönborn, J. Sielk and B. Hartke, J. Phys. Chem. A 2010, 114, 4036-4044.
Abstract:
We have assembled a global CASSCF potential energy surface for the excited 2A state of the cyclohexadiene -- hexatriene system, in two degrees of freedom, with full relaxation in all other degrees of freedom. Quantum wavepacket dynamics on this surface yields simple interpretations of recent experimental data on the ultrafast photochemical ring opening of cyclohexadiene as well as predictions on preferred product configurations. The feasibility of this system as a model for fulgide molecular switches is discussed.
BibTeX:
@article{Schoenborn2010,
author = {Schönborn, Jan Boyke and Sielk, J. and Hartke, Bernd},
title = {Photochemical ring opening of cyclohexadiene: Quantum wavepacket dynamics on a global ab initio potential energy surface},
journal = {J. Phys. Chem. A},
year = {2010},
volume = {114},
pages = {4036-4044},
doi = {https://doi.org/10.1021/jp909362c}
}
Coordination-Induced Spin Crossover (CISCO) through Axial Bonding of Substituted Pyridines to Nickel-Porphyrins: sigma-Donor vs pi-Acceptor Effects
S. Thies, C. Bornholdt, F. Köhler, F.D. Sönnichsen, C. Näther, F. Tuczek and R. Herges, Chem. Eur. J. 2010, 16, 9928-9937.
Abstract:
Ni-porphyrins with their rigid quadratic planar coordination framework provide an excellent model to study the coordination-induced spincrossover (CISCO) effect because bonding of one or two axial ligands to the metal center leads to a spin transition from S = 0 to S = 1. Herein both equilibrium constants K1S and K2, and for the first time also the corresponding thermodynamic parameters ΔH1S, ΔH2, ΔS1S, and ΔS2 are determined for the reaction of a nickel-porphyrin (Ni-tetrakis(pentafluorophenyl)porphyrin) with different 4-substituted pyridines by temperature dependent NMR spectroscopy. The association constants K1S and K2 are correlated with the basicity of the 4-substituted pyridines (R: OMe > H > CO2Et > NO2) whereas the ΔH1S values exhibit a completely different order (OMe < H > CO2Et > NO2). 4-nitropyridine exhibits the largest binding enthalpy which, however, is overcompensated by a large negative binding entropy. We attribute the large association enthalpy of nitropyridine with porphyrin to the back donation of electrons from the Ni dxz and dyz orbitals into the π∗ orbitals of pyridine and the negative association entropy to a decrease in vibrational and internal rotation entropy of the more rigid porphyrin-pyridine complex. Back donation for the nitro- and cyano-pyridine complexes is also confirmed by IR spectroscopy, showing a shift of the N-O and C-N vibrations, respectively, to lower wave numbers. X-ray structures of 2:1 complexes with nitro-, cyano- and dimethylaminopyridine provide further indication of a back donation. A further trend has been observed. The more basic the pyridine the larger is K1S relative to K2. For nitropyridine K2 is 17 times larger than K1S and in case of methoxypyridine K2 and K1S are almost equal.
BibTeX:
@article{Thies2010,
author = {Thies, Steffen and Bornholdt, Claudia and Köhler, Felix and Sönnichsen, Frank D. and Näther, Christian and Tuczek, Felix and Herges, Rainer},
title = {Coordination-Induced Spin Crossover (CISCO) through Axial Bonding of Substituted Pyridines to Nickel-Porphyrins: sigma-Donor vs pi-Acceptor Effects},
journal = {Chem. Eur. J.},
year = {2010},
volume = {16},
pages = {9928-9937},
doi = {https://doi.org/10.1002/chem.201000603}
}
Switching Single Azopyridine Supramolecules in Ordered Arrays on Au(111)
Y. Wang, X. Ge, G. Schull, R. Berndt, H. Tang, C. Bornholdt, F. Koehler and R. Herges, J. Am. Chem. Soc. 2010, 132, 1196-1197.
Abstract:
4,4-Azopyridine trimers and 4-phenylazopyridine dimers have been reversibly switched in ordered arrays on Au(111). During the switching process, single weak C−H...N hydrogen bonds are broken and reformed.
BibTeX:
@article{Wang2010,
author = {Wang, Yongfeng and Ge, Xin. and Schull, Guillaume. and Berndt, Richard and Tang, Hao. and Bornholdt, Claudia and Koehler, Felix and Herges, Rainer},
title = {Switching Single Azopyridine Supramolecules in Ordered Arrays on Au(111)},
journal = {J. Am. Chem. Soc.},
year = {2010},
volume = {132},
pages = {1196-1197},
doi = {https://doi.org/10.1021/ja9080277}
}
Atomic-Scale Control of Electron Transport through Single Molecules
Y. Wang, J. Kröger, R. Berndt, H. Vázquez, M. Brandbyge and M. Paulsson, Phys. Rev. Lett. 2010, 104, 176802.
Abstract:
Tin-phthalocyanine molecules adsorbed on Ag(111) were contacted with the tip of a cryogenic scanning tunneling microscope. Orders-of-magnitude variations of the single-molecule junction conductance were achieved by controllably dehydrogenating the molecule and by modifying the atomic structure of the surface electrode. Nonequilibrium Green’s function calculations reproduce the trend of the conductance and visualize the current flow through the junction, which is guided through molecule-electrode chemical bonds.
BibTeX:
@article{Wang2010a,
author = {Wang, Yongfeng and Kröger, Jörg and Berndt,Richard and Vázquez, Hector and Brandbyge, Mads and Paulsson, M.},
title = {Atomic-Scale Control of Electron Transport through Single Molecules},
journal = {Phys. Rev. Lett.},
year = {2010},
volume = {104},
pages = {176802},
doi = {https://doi.org/10.1103/PhysRevLett.104.176802}
}
Molecular Nanocrystals on Ultrathin NaCl Films on Au(111)
J. Wang, Y.F. and Kröger, R. Berndt and H. Tang, J. Am. Chem. Soc. 2010, 132, 12546-12547.
Abstract:
Direct comparison of SnPc growth on a metal and a nearly insulating surface was achieved by adsorption of SnPc on Au(111) partially covered with NaCl. While on Au(111), SnPc lies flat and grows in a Stranski−Krastanov mode; on NaCl, Volmer−Weber growth of three-dimensional molecular nanocrystals occurs. On NaCl, intermolecular interactions dominate over the molecule−NaCl coupling and result in a tilted adsorption configuration.
BibTeX:
@article{Wang2010b,
author = {Wang, Y. F. and Kröger, J. and Berndt, R. and Tang, H.},
title = {Molecular Nanocrystals on Ultrathin NaCl Films on Au(111)},
journal = {J. Am. Chem. Soc.},
year = {2010},
volume = {132},
pages = {12546-12547},
doi = {https://doi.org/10.1021/ja105110d}
}
Mounting Freestanding Molecular Functions onto Surfaces: The Platform Approach.
B. Baisch, D. Raffa, U. Jung, O. Magnussen, C. Nicolas, J. Lacour, J. Kubitschke and R. Herges, J. Am. Chem. Soc. 2009, 131, 442-443.
Abstract:
A modular system has been developed to mount mols. upright onto metal surfaces in a well controlled geometry. The approach is based on a reactive platform (triazatriangulenium salt) with an electrophilic center. Functional mols. are attached via C-C bond formation. The distance from the surface can be varied by a spacer, and the distance of the functional units from each other by the size of the platform. Self-assembly of the parent triazaangulenium salt as well as the functionalized platforms on Au(111) surfaces results in stable, hexagonally ordered adlayers.
BibTeX:
@article{Baisch2009,
author = {Baisch, Belinda and Raffa, Diego and Jung, Ulrich and Magnussen, Olaf and Nicolas, Cyril and Lacour, Jerome and Kubitschke, Jens and Herges, Rainer.},
title = {Mounting Freestanding Molecular Functions onto Surfaces: The Platform Approach.},
journal = {J. Am. Chem. Soc.},
year = {2009},
volume = {131},
pages = {442-443},
doi = {https://doi.org/10.1021/ja807923f}
}
Controlled Formation of an Axially Bonded Co-Phthalocyanine Dimer
X. Ge, C. Manzano, R. Berndt, L. Anger, F. Koehler and R. Herges, J. Am. Chem. Soc. 2009, 131, 6096-6098.
Abstract:
Isolated Co-phthalocyanine (CoPc) molecules were moved on a monolayer of CoPc on Cu(111) using an STM tip. If placed almost on top of another, the CoPc molecule in the second layer locks in place and the STM image at negative bias changes substantially. Density functional theory calculations explain the nature of the bonding mode and the change in STM.
BibTeX:
@article{Ge2009,
author = {Ge, Xin and Manzano, Carlos and Berndt, Richard and Anger, Lennart and Koehler, Felix and Herges, Rainer},
title = {Controlled Formation of an Axially Bonded Co-Phthalocyanine Dimer},
journal = {J. Am. Chem. Soc.},
year = {2009},
volume = {131},
pages = {6096-6098},
doi = {https://doi.org/10.1021/ja900484c}
}
2-(2,4-Dinitrobenzyl)pyridine (DNBP): A Potential Light-Activated Proton Shuttle.
C. Goeschen, R. Herges, J. Richter, B. Tokarczyk and J. Wirz, Helv. Chim. Acta 2009, 92, 1909-1922.
Abstract:
The well-known photochromic tautomerism of 2-(2,4-dinitrobenzyl)pyridine (1; CH; Scheme 1) was re-investigated by flash photolysis in aq. soln. in view of its potential application as a light-activated proton pump. Irradn. of 1 yields the enamine tautomer NH (λmax = 520 nm) that rapidly equilibrates with its conjugate base CNO- (λmax = 420 nm). The pH-rate profile for the first-order decay of NH and CNO- provides a direct detn. of the acidity const. of NH, pKa,cNH = 5.94±0.12 (I = 0.1M) and serves to clarify the mechanisms of proton transfer prevailing in aq. solns. The acidity const. of protonated 1 (CHNH+), pKa,cCHNH = 4.18 ± 0.02, was detd. by spectrophotometric titrn. [on SciFinder(R)]
BibTeX:
@article{Goeschen2009,
author = {Goeschen, Catrin and Herges, Rainer and Richter, Josef and Tokarczyk, Bogdan and Wirz, Jakob},
title = {2-(2,4-Dinitrobenzyl)pyridine (DNBP): A Potential Light-Activated Proton Shuttle.},
journal = {Helv. Chim. Acta},
year = {2009},
volume = {92},
pages = {1909-1922},
doi = {https://doi.org/10.1002/hlca.200900191}
}
Spatial modulation of /d/ states in a nanoscale Co island
T.G. Gopakumar, N. Neél, J. Kröger and R. Berndt, Chem. Phys. Lett. 2009, 484, 59-63.
Abstract:
A cryogenic scanning tunnelling microscope was used to probe the electronic properties of a moiré pattern observed from cobalt islands on Ag(1 1 1). Spatially resolved spectroscopy reveals that the moiré lattice gives rise to a periodic electronic pattern of cobalt /d/ states. The arrangement of magnetic molecules on the moiré lattice suggests an electronic template effect.
BibTeX:
@article{Gopakumar2009,
author = {Gopakumar, T. G. and Neél, N. and Kröger, J. and Berndt, R.},
title = {Spatial modulation of /d/ states in a nanoscale Co island},
journal = {Chem. Phys. Lett.},
year = {2009},
volume = {484},
pages = {59-63},
doi = {https://doi.org/10.1016/j.cplett.2009.11.012}
}
Crystal structure of 1,4'''-Dimethoxy-4,1':4',1'':4'',1'''-quaterphenylene
J. Iwicki, C. Näther, M. Schiek, A. Lützen, H.W. Rubahn, W. Krüger, K. Roßnagel and L. Kipp, Mat. Lett. 2009, 63, 2399-2401.
Abstract:
1,4triple prime-Dimethoxy-4,1′:4′,1″:4″,1triple prime-quaterphenylene crystallizes in space group Pbca with a = 7.4989(5) Å, b = 6.1544(3) Å, c = 40.359(2) Å, V = 1862.6(2) Å3, and Z = 4. In the crystal structure the molecules are arranged in layers, which are stacked in the direction of the crystallographic c-axis. The torsion between the molecules in a layer amounts to 69.06° resulting in a herringbone structure. The phenyl rings of the molecule are approximately planar with a torsion angle of 4.64° between the outer and the center rings. UV/Vis transmission measurements of the colorless crystal reveal a band gap of   3.2 eV.
BibTeX:
@article{Iwicki2009,
author = {Iwicki, Jaroslaw and Näther, Christian and Schiek, M. and Lützen, A. and Rubahn, H. W. and Krüger, W. and Roßnagel, Kai and Kipp, Lutz},
title = {Crystal structure of 1,4'''-Dimethoxy-4,1':4',1'':4'',1'''-quaterphenylene},
journal = {Mat. Lett.},
year = {2009},
volume = {63},
pages = {2399-2401},
doi = {https://doi.org/10.1016/j.matlet.2009.07.054}
}
Brownian molecular rotors: Theoretical design principles and predicted realizations
J.B. Schoenborn, R. Herges and B. Hartke, J. Chem. Phys. 2009, 130, 234906.
Abstract:
We propose simple design concepts for molecular rotors driven by Brownian motion and external photochemical switching. Unidirectionality and efficiency of the motion is measured by explicit simulations. Two different molecular scaffolds are shown to yield viable molecular rotors when decorated with suitable substituents.
BibTeX:
@article{Schoenborn2009,
author = {Schoenborn, Jan Boyke and Herges, Rainer and Hartke, Bernd},
title = {Brownian molecular rotors: Theoretical design principles and predicted realizations},
journal = {J. Chem. Phys.},
year = {2009},
volume = {130},
pages = {234906},
doi = {https://doi.org/10.1063/1.3148223}
}
Passing Current through Touching Molecules
G. Schull, T. Frederiksen, M. Brandbyge and R. Berndt, Phys. Rev. Lett. 2009, 103, 206803.
Abstract:
The charge flow from a single C60 molecule to another one has been probed. The conformation and electronic states of both molecules on the contacting electrodes have been characterized using a cryogenic scanning tunneling microscope. While the contact conductance of a single molecule between two Cu electrodes can vary up to a factor of 3 depending on electrode geometry, the conductance of the C60-C60 contact is consistently lower by 2 orders of magnitude. First-principles transport calculations reproduce the experimental results, allow a determination of the actual C60-C60 distances, and identify the essential role of the intermolecular link in bi- and trimolecular chains.
BibTeX:
@article{Schull2009,
author = {Schull, Guillaume and Frederiksen, Thomas and Brandbyge, Mads and Berndt, Richard},
title = {Passing Current through Touching Molecules},
journal = {Phys. Rev. Lett.},
year = {2009},
volume = {103},
pages = {206803},
doi = {https://doi.org/10.1103/PhysRevLett.103.206803}
}
Ultrashort Fluorescence Lifetimes of Hydrogen-Bonded Base Pairs of Guanosine and Cytidine in Solution
N.K. Schwalb, T. Michalak and F. Temps, J. Phys. Chem. B 2009, 113, 16365-16376.
Abstract:
The optically excited electronic states of hydrogen-bonded homo- and heterodimers of guanosine (G) and deoxycytidine (C) were investigated by femtosecond fluorescence up-conversion spectroscopy. The base pairs were prepared in CHCl3 solution by employing tert-butyldimethylsilyl (TBDMS) groups at the OH positions of the ribose (G) or deoxyribose (C) moieties to enhance the solubilities of the nucleosides in organic solvents. The H-bonded complexes that were obtained were characterized by FTIR spectroscopy. Fluorescence lifetime measurements were performed following electronic excitation at a series of UV wavelengths from λpump = 294 nm, close to the electronic origins of the bases, to λpump = 262 nm, where significant excess vibronic energy is deposited in the molecules, at nucleoside concentrations of c0 = 0.1 and 1.0 mM. The experimental results revealed the existence of an ultrafast deactivation pathway for the optically prepared electronically excited state(s) of the G·C Watson−Crick base pair, which was found to have a lifetime of τGC = 0.30(3) ps (with 2σ error limits) irrespective of the pump wavelength. A similar short decay time, τGG = 0.32(2) ps, was observed for the respective excited G·G homodimer. In contrast, the excited G monomer displayed a significantly longer-lived and wavelength-dependent deactivation, requiring three time constants, between 0.43(6) ps ≤ τG,1 ≤ 1.2(1) ps, 4.2(8) ps ≤ τG,2 ≤ 8(1) ps, and τG,3 = 195(32) ps. Self-complexation of C, on the other hand, led to a longer-lived excited state with a lifetime estimated between 1 ps ≤ τCC ≤ 10 ps, compared to the dominant initial subpicosecond decay time of the C monomer of τC,1 = 0.80(4) ps.
BibTeX:
@article{Schwalb2009,
author = {Schwalb, Nina K. and Michalak, Thomas and Temps, Friedrich},
title = {Ultrashort Fluorescence Lifetimes of Hydrogen-Bonded Base Pairs of Guanosine and Cytidine in Solution},
journal = {J. Phys. Chem. B},
year = {2009},
volume = {113},
pages = {16365-16376},
doi = {https://doi.org/10.1021/jp904883n}
}
Quantum-mechanical wavepacket propagation in a sparse, adaptive basis of interpolating Gaussians with collocation
J. Sielk, H. von Horsten, F. Krueger, R. Schneider and B. Hartke, Phys. Chem. Chem. Phys. 2009, 11, 463-475.
Abstract:
We present an extension of our earlier work on adaptive quantum wavepacket dynamics [Phys. Chem. Chem. Phys. 8 (2006) 3627]. In this dynamically pruned basis representation the wavepacket is only stored at places where it has non-negligible contributions. Here we enhance the former 1D proof-of-principle implementation to higher dimensions and optimize it by a new basis set, interpolating Gaussians with collocation. As a further improvement the Tnum approach from Lauvergnat et al. was implemented, which in combination with our adaptive representation offers the possibility to calculate the whole Hamiltonian on the fly. For a two-dimensional artifical benchmark and a three-dimensional real-life test case, we show that a sparse matrix implementation of this approach saves memory compared to traditional basis representations and comes even close to the efficiency of the fast Fourier transform method. Thus we arrive at a quantum wavepacket dynamics implementation featuring several important black-box characteristics: It can treat arbitrary systems without code changes, it calculates the kinetic and potential part of the Hamiltonian on the fly, and it employs a basis that is automatically optimized for the ongoing wavepacket dynamics.
BibTeX:
@article{Sielk2009,
author = {Sielk, J. and von Horsten, H.F. and Krueger, F. and Schneider, R. and Hartke, Bernd},
title = {Quantum-mechanical wavepacket propagation in a sparse, adaptive basis of interpolating Gaussians with collocation},
journal = {Phys. Chem. Chem. Phys.},
year = {2009},
volume = {11},
pages = {463-475},
doi = {https://doi.org/10.1039/b814315c}
}
Highly Efficient Reversible Z−E Photoisomerization of a Bridged Azobenzene with Visible Light through Resolved S1(nπ*) Absorption Bands
R. Siewertsen, H. Neumann, B. Buchheim-Stehn, R. Herges, C. Naether, F. Renth and F. Temps, J. Am. Chem. Soc. 2009, 131, 15594 - 15595.
Abstract:
The reversible Z−E photoswitching properties of the (Z) and (E) isomers of the severely constrained bridged azobenzene derivative 5,6-dihydrodibenzo[c,g][1,2]diazocine (1) were investigated quantitatively by UV/vis absorption spectroscopy in solution in n-hexane. In contrast to normal azobenzene (AB), 1 has well separated S1(nπ*) absorption bands, peaking at λZ = 404 nm and λE = 490 nm. Using light at λ = 385 nm, it was found that 1Z can be switched to 1E with very high efficiency, Γ = 92 ± 3%. Conversely, 1E can be switched back to 1Z using light at λ = 520 nm with 100% yield. The measured quantum yields are ΦZ→E = 72 ± 4% and ΦE→Z = 50 ± 10%. The thermal lifetime of the (E) isomer is 4.5 ± 0.1 h at 28.5 °C. The observed photochromic and photoswitching properties of 1 are much more favorable than those for normal AB, making our title compound a promising candidate for interesting applications as a molecular photoswitch especially at low temperatures. The severe constraints by the ethylenic bridge apparently do not hinder but favor the Z−E photoisomerization reactions.
BibTeX:
@article{Siewertsen2009,
author = {Siewertsen, Ron and Neumann, Hendrikje and Buchheim-Stehn, Bengt and Herges, Rainer and Naether, Christian and Renth, Falk and Temps, Friedrich},
title = {Highly Efficient Reversible Z−E Photoisomerization of a Bridged Azobenzene with Visible Light through Resolved S1(nπ*) Absorption Bands},
journal = {J. Am. Chem. Soc.},
year = {2009},
volume = {131},
pages = {15594 - 15595},
doi = {https://doi.org/10.1021/ja906547d}
}
Parallel ultrafast E-C Ring closure and E-Z isomerization in a photochromic furylfulgide studied by femtosecond time-resolved spectroscopy
R. Siewertsen, F. Renth, F. Temps and F. Soennichsen, Phys. Chem. Chem. Phys. 2009, 11, 5952-5961.
Abstract:
The photo-induced parallel E - C ring closure and E - Z isomerisation reactions of the (E) isomer of the photochromic furylfulgide 2-[1-(2,5-dimethyl-3-furyl)-ethylidene]-3-isopropylidene succinic anhydride (1) in n-hexane have been studied using femtosecond time-resolved spectroscopy. Broadband transient absorption data after femtosecond laser excitation at lpump = 335 nm provide time constants of 100 fs and 250 fs that belong to the formation of the (C) and the (Z) isomers, respectively, to yield a (C):(Z) product ratio of about 2:1. The results are consistent with a conformer-specific photoreaction of the (E)-isomer of 1, where one conformer (alpha) undergoes predominantly E - C ring closure and the other (beta) E - Z isomerisation, or alternatively with an ultrafast branching of the excited wavepacket of the alpha-conformer within Delta t < 250 fs after the pump pulse. The observed isomerisation times suggest that the ensuing transformations proceed via distinctive conical intersections between the respective potential energy hypersurfaces. Oscillations of the transient absorption with frequencies of approx. 64 and 114 cm-1 are found and interpreted as excited-state vibrations induced during the E - Z isomerisation reaction. Slower spectral dynamics at delay times up to approx. 10 ps reflect the cooling of the vibrationally hot reactant and product molecules after their return to their electronic ground states. Time-dependent DFT calculations were performed to shed light on the reaction coordinates involved. The emerging picture for the dynamics of 1 obtained in this work is of interest in the broader context for our understanding of conformer-specific photochemistry and competing ultrafast reactions in polyatomic molecules.
BibTeX:
@article{Siewertsen2009a,
author = {Siewertsen, Ron and Renth, Falk and Temps, Friedrich and Soennichsen, Frank},
title = {Parallel ultrafast E-C Ring closure and E-Z isomerization in a photochromic furylfulgide studied by femtosecond time-resolved spectroscopy},
journal = {Phys. Chem. Chem. Phys.},
year = {2009},
volume = {11},
pages = {5952-5961},
doi = {https://doi.org/10.1039/b821344e}
}
Supramolecular Patterns controlled by Electron Interference and Direct Intermolecular Interactions
Y. Wang, X. Ge, C. Manzano, J. Kröger, R. Berndt, W. Hofer, H. Tang and J. Cerda, J. Am. Chem. Soc. 2009, 131, 10400-10402.
Abstract:
Whereas all 230 three-dimensional space groups occur in organic crystals, out of only 17 plane groups some highly symmetric ones such as p31m have not yet been observed in two-dimensional (2D) crystals of organic molecules. Here a kagome network with p31m symmetry is reported for cobalt phthalocyanine on Cu(111). This unusual structure results from substrate-induced reduction of molecular symmetry and substrate-mediated interaction via quantum interference of surface electrons. These interactions provide additional control over the symmetry of 2D crystals of phthalocyanines and lead to a variety of other symmetries in self-assembled arrays.
BibTeX:
@article{Wang2009b,
author = {Wang, Y. and Ge, X. and Manzano, C. and Kröger, Jörg and Berndt, Richard and Hofer, W. and Tang, H. and Cerda, J.},
title = {Supramolecular Patterns controlled by Electron Interference and Direct Intermolecular Interactions},
journal = {J. Am. Chem. Soc.},
year = {2009},
volume = {131},
pages = {10400-10402},
doi = {https://doi.org/10.1021/ja903506s}
}
Pushing and Pulling a Sn Ion through an Adsorbed Phthalocyanine Molecule
Y. Wang, J. Kröger, R. Berndt and W. Hofer, J. Am. Chem. Soc. 2009, 131, 3639-3643.
Abstract:
Molecule-based functional devices on surfaces may take advantage of bistable molecular switches. The conformational dynamics and efficiency of switches are radically different on surfaces compared to liquid phase. We present a design of molecular layers, which enables bistable switching on a surface, and, for the first time, demonstrate control of a single switch in a dense and ordered array at the spatial limit. Up and down motion of a central Sn ion through the frame of a phthalocyanine molecule is achieved via resonant electron or hole injection into molecular orbitals.
BibTeX:
@article{Wang2009,
author = {Wang, Yongfeng and Kröger, Joerg and Berndt, Richard and Hofer, Werner},
title = {Pushing and Pulling a Sn Ion through an Adsorbed Phthalocyanine Molecule},
journal = {J. Am. Chem. Soc.},
year = {2009},
volume = {131},
pages = {3639-3643},
doi = {https://doi.org/10.1021/ja807876c}
}
Structural and Electronic Properties of Ultrathin Tin-Phthalocyanine Films on Ag(111) at the Single-Molecule Level
Y. Wang, J. Kröger, R. Berndt and W. Hofer, Angew. Chem. 2009, 121, 1287-1291.
Abstract:
Organic electronic and optoelectronic devices such as light-emitting diodes, field-effect transistors and photovoltaic devices have received considerable attention recently because organic materials can be cheap, light and flexible. The device performance is intimately coupled to charge transfer at inorganic-organic as well as at organic-organic interfaces. Understanding the structural and electronic properties of organic thin films supported on surfaces is thus of fundamental interest. In this context, phthalocyanines are molecules with unique optical and electrical properties. They have been investigated by low-energy electron and X-ray diffraction, scanning electron microscopy, and photoelectron spectroscopy. Using scanning tunnelling microscopy (STM) with its unique subnanometer resolution, the geometric arrangement and electronic properties may be studied at the single molecule level. However, stable imaging is often hampered by an enhanced mobility of the molecules. Up to now, STM investigations mainly focussed on molecule aggregates with coverages around a single molecular layer.
BibTeX:
@article{Wang2009a,
author = {Wang, Yongfeng and Kröger, Joerg and Berndt, Richard and Hofer, Werner},
title = {Structural and Electronic Properties of Ultrathin Tin-Phthalocyanine Films on Ag(111) at the Single-Molecule Level},
journal = {Angew. Chem.},
year = {2009},
volume = {121},
pages = {1287-1291},
doi = {https://doi.org/10.1002/ange.200803305}
}
Local density of states from constant-current tunneling spectra
M. Ziegler, N. Néel, A. Sperl, J. Kröger and R. Berndt, Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 80, 125402.
Abstract:
Scanning tunneling spectroscopy of the differential conductance is performed at constant current and at constant distance. These modes of operation significantly affect peak positions and line shapes in spectra as well as patterns in spatial maps of the differential conductance. A normalization procedure for constant-current data, which relies on experimental current-distance data, is shown to yield spectral information on the local density of states.
BibTeX:
@article{Ziegler2009,
author = {Ziegler, M. and Néel, N. and Sperl, A. and Kröger, J. and Berndt, R.},
title = {Local density of states from constant-current tunneling spectra},
journal = {Phys. Rev. B: Condens. Matter Mater. Phys.},
year = {2009},
volume = {80},
pages = {125402},
doi = {https://doi.org/10.1103/PhysRevB.80.125402}
}
Magnetoelastic hysteresis in 5 M NiMnGa single crystals
C. Bechtold, A. Gerber, M. Wuttig and E. Quandt, Scripta Materialia 2008, 58, 1022-1024.
Abstract:
The magnetic field induced strain (MFIS) in a five-layered NiMnGa single crystal was investigated. Without compressive load, a maximum strain of 5.5% was measured. The hysteresis of the magnetoelastic strain was further characterized by biased minor loops at decreasing magnetic field amplitudes. In contrast to Joule magnetostrictors, the hysteresis widths were found to be independent of the field amplitude which results in a threshold field identical to the hysteresis width for any MFIS.
BibTeX:
@article{Bechtold2008,
author = {Bechtold, C. and Gerber, A. and Wuttig, M. and Quandt, Eckhard},
title = {Magnetoelastic hysteresis in 5 M NiMnGa single crystals},
journal = {Scripta Materialia},
year = {2008},
volume = {58},
pages = {1022-1024},
doi = {https://doi.org/10.1016/j.scriptamat.2008.01.035}
}
Equal intensity double plasmon resonance (EIDPR) of bimetallic quasi-nanocomposites based on sandwich geometry.
V.S.K. Chakravadhanula, M. Elbahri, U. Schürmann, H. Takele, H. Greve, V. Zaporojtchenko and F. Faupel, Nanotechnology 2008, 19, 225302.
Abstract:
We report a strategy to achieve a material showing equal intensity double plasmon resonance (EIDPR) based on sandwich geometry. We studied the interaction between localized plasmon resonances associated with different metal clusters (Au/Ag) on Teflon AF (TAF) in sandwich geometry. Engineering the EIDPR was done by tailoring the amount of Au/Ag and changing the TAF thickness. The samples were investigated by transmission electron microscopy (TEM) and UV–visible spectroscopy. Interestingly, and in agreement with the dipole–surface interaction, the critical barrier thickness for an optimum EIDPR was observed at 3.3 nm. The results clearly show a plasmon sequence effect and visualize the role of plasmon decay.
BibTeX:
@article{Chakravadhanula2008,
author = {Chakravadhanula, V. S. K. and Elbahri, M. and Schürmann, U. and Takele, H. and Greve, H. and Zaporojtchenko, V. and Faupel, Franz},
title = {Equal intensity double plasmon resonance (EIDPR) of bimetallic quasi-nanocomposites based on sandwich geometry.},
journal = {Nanotechnology},
year = {2008},
volume = {19},
pages = {225302},
doi = {https://doi.org/10.1088/0957-4484/19/22/225302}
}
Polymer-metal nanocomposites with 2-dimensional Au nanoparticle arrays for sensoric applications
C. Hanisch, A. Kulkarni, V. Zaporojtchenko and F. Faupel, Journal of Physics: Conference Series 2008, 100, 052043.
Abstract:
Sensors for volatile organic compounds (VOC) are of increasing interest for various applications ever since. Here we present a novel method to achieve a fast and reversible response by employing a polymer-metal nanocomposite film with 2-dimensional Au nanoparticle arrays. Our sensors are made out of spin-coated polymer substrates on which we deposit gold clusters with a cluster density near the percolation threshold via thermal evaporation. The sensor operates on the principle of swelling of polymers in the presence of VOC. This leads to a change in the interparticle distance and therefore the conductivity of the composites. The method is fast, easy, precisely to control and the sensor fabrication process produces only a minimum amount of waste (like organic solvents). The degree of swelling primarily depends on the type of polymer and the organic solvent, i.e. solubility parameters of the polymer and the vapor. Therefore, the pattern leads to fingerprints of particular polymers towards different vapors. These fingerprints can be employed as a parameter for detecting different VOCs.
BibTeX:
@article{Hanisch2008,
author = {Hanisch, C. and Kulkarni, A. and Zaporojtchenko, V. and Faupel, Franz},
title = {Polymer-metal nanocomposites with 2-dimensional Au nanoparticle arrays for sensoric applications},
journal = {Journal of Physics: Conference Series},
year = {2008},
volume = {100},
pages = {052043},
doi = {https://doi.org/10.1088/1742-6596/100/5/052043}
}
Structure and redox behavior of azobenzene-containing monolayers on Au(111): A combined STM, X-ray reflectivity, and voltammetry study
U. Jung, B. Baisch, D. Kaminski, K. Krug, A. Elsen, T. Weineisen, D. Raffa, J. Stettner, C. Bornholdt, R. Herges and O. Magnussen, Journal of Electroanalytical Chemistry 2008, 619-620, 152-158.
Abstract:
A combined structural and electrochemical study of self-assembled monolayers of the azobenzene-containing alkane thiol N-(2-mercaptoethyl)-4-phenylazobenzamide on Au(1 1 1) by scanning tunneling microscopy, synchrotron X-ray reflectivity, and cyclic voltammetry is presented. Densely packed monolayers are observed, in which the molecules are arranged in chains forming an ordered View the MathML source structure with a coverage of 2/7 ML. The molecules are tilted by 40° relative to the surface normal, resulting in a monolayer thickness of 13.7 Å. A total charge of 65.2 ± 4.3 μC/cm2 corresponding to 1e- per molecule and apparent electron transfer coefficients of ca.0.5 are found.
BibTeX:
@article{Jung2008,
author = {Jung, Ulrich and Baisch, Belinda and Kaminski, Daniel and Krug, Klaus and Elsen, Annika and Weineisen, Tobias and Raffa, Diego and Stettner, Jochim and Bornholdt, Claudia and Herges, Rainer and Magnussen, Olaf},
title = {Structure and redox behavior of azobenzene-containing monolayers on Au(111): A combined STM, X-ray reflectivity, and voltammetry study},
journal = {Journal of Electroanalytical Chemistry},
year = {2008},
volume = {619-620},
pages = {152-158},
doi = {https://doi.org/10.1016/j.jelechem.2008.04.002}
}
Nonadiabatic effects on surfaces: Kohn anomaly, electronic damping of adsorbate vibrations, and local heating of single molecules
J. Kröger, J. Phys. Condens. Matter 2008, 20, 224015.
Abstract:
Three aspects of electron–phonon coupling at metal surfaces are reviewed. One aspect is the Kohn effect, which describes an anomalous dispersion relation of surface phonons due to quasi-one-dimensional nesting of Fermi surface contours. The combination of electron energy loss spectroscopy and angle-resolved photoelectron spectroscopy allows us to unambiguously characterize Kohn anomaly systems. A second aspect is the nonadiabatic damping of adsorbate vibrations. Characteristic spectroscopic line shapes of vibrational modes allow us to estimate the amount of energy transfer between the vibrational mode and electron–hole pairs. Case studies of a Kohn anomaly and nonadiabatic damping are provided by the hydrogen- and deuterium-covered Mo(110) surface. As a third aspect of interaction between electrons and phonons, local heating of a C60 molecule adsorbed on Cu(100) and in contact with the tip of a scanning tunnelling microscope is covered.
BibTeX:
@article{Kroeger2008a,
author = {Kröger, Jörg},
title = {Nonadiabatic effects on surfaces: Kohn anomaly, electronic damping of adsorbate vibrations, and local heating of single molecules},
journal = {J. Phys. Condens. Matter},
year = {2008},
volume = {20},
pages = {224015},
doi = {https://doi.org/10.1088/0953-8984/20/22/224015}
}
Contact to single atoms and molecules with the tip of a scanning tunnelling microscope.
J. Kröger, N. Neel and L. Limot, J. Phys.: Condens. Matter 2008, 20, 223001/1-223001/16.
Abstract:
A review. Expts. using the tip of a scanning tunnelling microscope to contact atoms and mols. adsorbed on surfaces are reviewed. Conductance quantization upon forming or breaking a contact between the tip and surfaces as well as between the tip and specifically chosen atoms and MOs is addressed. Imaging the contact area prior to and after contact measurements allows one to monitor the status of the contacted object as well as that of the contacting electrodes. Spectroscopy with the tip in contact with individual atoms or mols. reveals the reproducibility of and control over such expts. today.
BibTeX:
@article{Kroeger2008,
author = {Kröger, J. and Neel, N. and Limot, L.},
title = {Contact to single atoms and molecules with the tip of a scanning tunnelling microscope.},
journal = {J. Phys.: Condens. Matter},
year = {2008},
volume = {20},
pages = {223001/1-223001/16},
doi = {https://doi.org/10.1088/0953-8984/20/22/223001}
}
Conductance of Oriented C60 Molecules.
N. Neel, J. Kröger, L. Limot and R. Berndt, Nano Lett. 2008, 8, 1291-1295.
Abstract:
C60 mols. adsorbed to Cu(100) are contacted with the tip of a cryogenic scanning tunneling microscope. Images with submol. resoln. reveal distinct orientations of the mols. We find that the orientation significantly affects the conductance of the contact despite the high symmetry of C60.
BibTeX:
@article{Neel2008,
author = {Neel, Nicolas and Kröger, Joerg and Limot, Laurent and Berndt, Richard.},
title = {Conductance of Oriented C60 Molecules.},
journal = {Nano Lett.},
year = {2008},
volume = {8},
pages = {1291-1295},
doi = {https://doi.org/10.1021/nl073074i}
}
Probing the Conductance of Single Atoms and Molecules
N. Neel, J. Kröger, L. Limot and R. Berndt, J. Scann. Probe Microsc. 2008, 3, 9-12.
Abstract:
Contact between the tip of a low-temperature scanning tunnelling microscope and single atoms and molecules is investigated. In a controlled and reproducible way clean Ag(111) surfaces, individual silver atoms on Ag(111) as well as individual Co atoms and C60 molecules adsorbed on Cu(100) are contacted. Upon contact the conductance changes discontinuously in the case of the tip-surface junction while the tip-atom and tip-molecule junctions exhibit a continuous transition from the tunnelling to the contact regime. Spectroscopy in the contact regime on Co atoms on Cu(100) shows significant change of the Kondo temperature. Conductance curves of C60 molecules indicate fluctuations induced by heating of the junction.
BibTeX:
@article{Neel2008a,
author = {Neel, N. and Kröger, Jörg and Limot, L. and Berndt, Richard},
title = {Probing the Conductance of Single Atoms and Molecules},
journal = {J. Scann. Probe Microsc.},
year = {2008},
volume = {3},
pages = {9-12},
doi = {https://doi.org/10.1166/jspm.2008.006}
}
Rotation of C60 in a single-molecule contact.
N. Neel, L. Limot, J. Kröger and R. Berndt, Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 77, 125431/1-125431/5.
Abstract:
The tip of a low-temp. scanning tunneling microscope is moved vertically into contact with single C60 mols. on Cu(100), while monitoring the current. Three of five obsd. mol. orientations on the copper surface display rotations of their adsorption configuration when approaching the tip beyond a threshold value. Possible mechanisms for the tip-induced rotation are discussed.
BibTeX:
@article{Neel2008b,
author = {Neel, N. and Limot, L. and Kröger, J. and Berndt, R.},
title = {Rotation of C60 in a single-molecule contact.},
journal = {Phys. Rev. B: Condens. Matter Mater. Phys.},
year = {2008},
volume = {77},
pages = {125431/1-125431/5},
doi = {https://doi.org/10.1103/PhysRevB.77.125431}
}
Azo Supramolecules on Au(111) with Controlled Size and Shape.
Y. Wang, X. Ge, G. Schull, R. Berndt, C. Bornholdt, F. Koehler and R. Herges, J. Am. Chem. Soc. 2008, 130, 4218-4219.
Abstract:
Using a subtle balance between weak intermol. C-H...N hydrogen bonds and mol.-surface interactions, supramols. of azobenzene-related mols. on Au surfaces were prepd. For anal., modeling based on 1st-principles calcns. was performed.
BibTeX:
@article{Wang2008,
author = {Wang, Yongfeng and Ge, Xin and Schull, Guillaume and Berndt, Richard and Bornholdt, Claudia and Koehler, Felix and Herges, Rainer.},
title = {Azo Supramolecules on Au(111) with Controlled Size and Shape.},
journal = {J. Am. Chem. Soc.},
year = {2008},
volume = {130},
pages = {4218-4219},
doi = {https://doi.org/10.1021/ja710414b}
}
Functional Polymer Nanocomposites
V. Zaporojtchenko, T. Strunskus, H. Greve, U. Schürmann, H. Takele, C. Hanisch, V.S.K. Chakravadhanula, N. Ni, A. Gerber, E. Quandt, R. Podschun and F. Faupel, Polymers & Polymer Composites 2008, 16, 471-481.
Abstract:
While extensive research has been carried out in the field of structural polymer-based nanocomposites much less investigations have been concerned with polymer nanocomposites for functional applications. Among the functional nanomaterials, nanocomposites consisting of metal nanoparticles dispersed in a dielectric matrix are of particular interest due to their novel functional properties offering hosts of new applications. Here, polymers are attractive as matrix, and several approaches have been reported to incorporate metal nanoparticles into polymers. The present review is concerned with the preparation of polymer-based nanocomposites by vapor phase co-and tandem deposition and the resulting functional properties. The techniques involve evaporation and sputtering, respectively, of metallic and organic components and inter alia allow the preparation of composites which contain alloy clusters of well defined composition. Emphasis is placed on soft-magnetic high frequency materials with cut-off frequencies well above 1 GHz and on optical composites with tuned plasmon resonances suitable for ultra thin color filters, Bragg reflectors, and other devices. In addition, antibacterial coatings and sensors for organic vapors are addressed. The latter take advantage of the steep drop of the electrical resistivity at the percolation threshold. First results are also reported on the incorporation of photo-switchable molecules into nanocomposites near the percolation threshold. Moreover, a novel approach to produce magnetic nanorods is presented.
BibTeX:
@article{Zaporojtchenko2008,
author = {Zaporojtchenko, Vladimir and Strunskus, Thomas and Greve, Henry and Schürmann, Ulrich and Takele, Haile and Hanisch, Christian and Chakravadhanula, Venkata Sai Kiran and Ni, Na and Gerber, Andreas and Quandt, Eckhard and Podschun, Rainer and Faupel, Franz},
title = {Functional Polymer Nanocomposites},
journal = {Polymers & Polymer Composites},
year = {2008},
volume = {16},
pages = {471-481}
}
Links between potential energy structures and quantum cumulative reaction probabilities of double proton transfer reactions.
H.F. von Horsten and B. Hartke, Chem. Phys. 2007, 338, 160-167.
Abstract:
Double proton transfer reactions of pyrazole-guanidine species exhibit unusual energy profiles of a plateau form, different from the std. single and double barrier shapes. We have demonstrated earlier that this leads to a characteristically different quantum dynamical behavior of plateau reactions, when measured appropriately. Here we show that these differences also carry over to traditional measures of reaction probability.
BibTeX:
@article{Horsten2007,
author = {von Horsten, H. F. and Hartke, B..},
title = {Links between potential energy structures and quantum cumulative reaction probabilities of double proton transfer reactions.},
journal = {Chem. Phys.},
year = {2007},
volume = {338},
pages = {160-167},
doi = {https://doi.org/10.1016/j.chemphys.2007.03.011}
}
Orientationally Ordered (7 * 7) Superstructure of C60 on Au(111).
G. Schull and R. Berndt, Phys. Rev. Lett. 2007, 99, 226105/1-226105/4.
Abstract:
Long range orientational order within C60 monolayers on Au(111) is obsd. with low-temp. scanning tunneling microscopy. A unit cell comprised of 49 mols. which adopt 11 different orientations is found. It can be divided in a faulted and an unfaulted half similar to the (7 * 7) reconstruction of Si(111). A model is proposed which shows how, through a Moire-like effect, the substrate induces minute changes in the orientation of the C60 mols. Intermol. interactions play a major role in stabilizing the superlattice.
BibTeX:
@article{Schull2007,
author = {Schull, G. and Berndt, R.},
title = {Orientationally Ordered (7 * 7) Superstructure of C60 on Au(111).},
journal = {Phys. Rev. Lett.},
year = {2007},
volume = {99},
pages = {226105/1-226105/4},
doi = {https://doi.org/10.1103/PhysRevLett.99.226105}
}
Ultrafast Electronic Relaxation in Guanosine is Promoted by Hydrogen Bonding with Cytidine.
N.K. Schwalb and F. Temps, J. Am. Chem. Soc. 2007, 129, 9272-9273.
Abstract:
The excited electronic state lifetime of the guanosine-cytidine (G...C) Watson-Crick (WC) base pair has been directly measured in comparison to free G and C. Measurements have been carried out in soln. in chloroform, where the formation of H-bonded base pairs is strongly favored, using the technique of femtosecond fluorescence up-conversion spectroscopy. The results show that the formation of the H-bonded WC pair leads to steep acceleration of the ultrafast nonradiative electronic deactivation compared to the free nucleosides, esp. G, which can be explained by an intermol. G-to-C electron-induced proton-transfer mechanism in the excited state. The results are of vital interest for bridging the huge gap between the well-known electronic properties of the isolated nucleobases and the strikingly different dynamics of DNA mols.
BibTeX:
@article{Schwalb2007,
author = {Schwalb, Nina K. and Temps, Friedrich.},
title = {Ultrafast Electronic Relaxation in Guanosine is Promoted by Hydrogen Bonding with Cytidine.},
journal = {J. Am. Chem. Soc.},
year = {2007},
volume = {129},
pages = {9272-9273},
doi = {https://doi.org/10.1021/ja073448+}
}
Ultrafast transient absorption spectroscopy of the photoinduced Z-E isomerization of a photochromic furylfulgide.
F. Renth, M. Foca, A. Petter and F. Temps, Chem. Phys. Lett. 2006, 428, 62-67.
Abstract:
The photoinduced Z-E isomerization of a photochromic furylfulgide following excitation at 387 nm was studied using time-resolved transient absorption spectroscopy with probing from 410 to 690 nm in ethanol as solvent. The excited-state absorption decayed dominantly on a time scale of 220 fs. An oscillatory behavior was interpreted as vibrational coherence involving a low-frequency torsional motion. A slow component with a decay time of 4.1 ps was assigned to hot ground state absorption. At 25 ps, the transient absorption resembled the stationary E-Z difference spectrum. The results indicate that the Z-E photoisomerization proceeds on a sub-ps time scale.
BibTeX:
@article{Renth2006,
author = {Renth, F. and Foca, M. and Petter, A. and Temps, F..},
title = {Ultrafast transient absorption spectroscopy of the photoinduced Z-E isomerization of a photochromic furylfulgide.},
journal = {Chem. Phys. Lett.},
year = {2006},
volume = {428},
pages = {62-67},
doi = {https://doi.org/10.1016/j.cplett.2006.07.036}
}
Femtosecond fluorescence up-conversion spectroscopy of a rotation-restricted azobenzene after excitation to the S1 state.
T. Pancur, F. Renth, F. Temps, B. Harbaum, A. Krueger, R. Herges and C. Naether, Phys. Chem. Chem. Phys. 2005, 7, 1985-1989.
Abstract:
Femtosecond time-resolved fluorescence up-conversion spectroscopy has been used in a study of the photo-induced isomerization reactions of a rotation-restricted trans-azobenzene (trans-AB) deriv. capped by a crown ether (I), a chem. similar open deriv. (II), and unsubstituted trans-AB (3) after excitation to the S1 (npi*) state at l = 475 nm in dioxane soln. The obsd. biexponential temporal fluorescence profiles for I and II were almost indistinguishable within exptl. error. The fitted fast fluorescence decay times (+-2s) for the two compds. were t1 (I) = (0.79 +- 0.20) and t1 (II) = (1.05 +- 0.20) ps, compared to t1 (3) = (0.37 +- 0.06) ps. The second decay components could be described with t2 (I) = (20.3 +- 9.5) resp. t2 (II) = (19.0 +- 6.0) ps, vs. t2 (3) = (3.26 +- 0.85) ps. The very similar lifetimes strongly suggest that trans-cis isomerization of I and II after S1 excitation is governed by the same mechanism. Since I cannot isomerize by a simple large-amplitude rotation of one of the Ph rings about the central NN bond, the isomerization dynamics of both ABs should be better described as "inversion" at the N atom(s) rather than large-amplitude "rotation".
BibTeX:
@article{Pancur2005,
author = {Pancur, T. and Renth, F. and Temps, F. and Harbaum, B. and Krueger, A. and Herges, R. and Naether, Chr.},
title = {Femtosecond fluorescence up-conversion spectroscopy of a rotation-restricted azobenzene after excitation to the S1 state.},
journal = {Phys. Chem. Chem. Phys.},
year = {2005},
volume = {7},
pages = {1985-1989},
doi = {https://doi.org/10.1039/b419236b}
}

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