Realizing molecular “Designer Solids” by programmed assembly of building units taken form libraries is a very appealing objective. Recently, metal-organic frameworks (MOFs) have attracted a huge interest in this context. Here, we will focus on the integration of molecular switches into MOFs, as well as on several applications based on these highly versatile crystalline materials. For numerous MOF-based applications the conventional solvothermal synthesis yielding powders is not well suited, e.g. in optics the powder particles cause strong scattering which makes a reliable determination of photophysical parameters difficult. To overcome these problems, we have developed a layer-by-layer (lbl) deposition method to produce well-defined, highly oriented and monolithic MOF thin films on a number of different substrates. The resulting films are referred to as SURMOFs [1,2]. The fabrication of hetero-multilayers (see Fig. 1) is rather straightforward with this lbl method. In this talk, we will describe the principles of SURMOF fabrication as well as the results of systematic investigations of electrical and photophysical properties exhibited by empty MOFs and after loading their pores with functional guests. Subsequently we will focus on the implementation of molecular switches into SURMOFs, and the application for a variety of purposes.

References:
[1] J. Liu, Ch. Wöll, Chem. Soc. Rev. 46, 5730-5770 (2017)
[2] L. Heinke, Ch. Wöll, Advanced Materials 31 (26), 1970184 (2019)

abstract not yet available

abstract not yet available

Photoresponsive smart materials transform light energy into sophisticated functions.[1] They find increasing biomedical applications in light-induced drug release and photopharmacology, as they can locally provide the desired therapeutic effect due to precise spatiotemporal dosage control. However, the majority of reported studies rely on cytotoxic UV light that poorly penetrates tissues.[2] We have introduced a first photochromic low-MW supramolecular hydrogel that releases drugs under visible light irradiation.[3] This was achieved by coupling a previously developed low-molecular-weight hydrogelator with a fluorinated azobenzene motif switchable with green light.[4] The resulting hydrogels can encapsulate structurally unmodified drugs, as well as proteins. The cargo is efficiently released upon exposure on visible light. We demonstrated green-light-induced release of structurally unmodified antibiotic, anticancer, and anti-inflammatory drugs under physiological conditions. Using the antibiotic-loaded gel, we selectively inhibited bacterial growth with green light.

Upon investigation of potential guests for the hydrogel system, we have discovered peptoids of light-dependent cytotoxicity.[5] Our recent progress in the area of visible light-triggered hydrogels and photopharmacology will be presented.

References:
[1] Z. Pianowski Chem. Eur. J. 2019, 25, 5128-5144.
[2] I. Tomatsu, L. Peng, A. Kross. Adv. Drug Delivery Rev. 2011, 63, 1257.
[3] J. Karcher, Z. Pianowski, Chem. Eur. J. 2018, 24, 11605-11610
[4] D. Bleger, et al. J. Am. Chem. Soc. 2012, 134, 20597.
[5] Z. Pianowski et al. “Diketopiperazine mit licht-aktivierter Zytotoxizität” Patent application (DPMA) priority date 12.07.2019

Photochromic molecular switches based on excited-state intramolecular proton transfer (ESIPT) belong to the fastest chemical processes known. Hence, competing side reactions are virtually impossible and exceptional photostabilities can be reached. Based on quasi-static theoretical calculations, Sobolewski et al. [Phys. Chem. Chem. Phys.2008, 10, 1243] proposed a new combination of ESIPT processes with intermediate, torsional motion of a“crane” group. The net result of the desired ESIPT-crane-ESIPT steps is a medium-range transport of the proton along the molecular scaffold:

In Project A7, we investigate the photo-induced molecular mechanisms and dynamics of such prototypical photochromic switches that combine ESIPT and crane features, by joining forces from Physical Chemistry (femtosecond spectroscopy), Organic Chemistry (synthesis), and Theoretical Chemistry (quantum-chemical molecular dynamics calculations).

A rational molecular design of such systems calls for a variety of cranes and of proton donor and acceptor groups, and for ensuring solubility in solvents that do not interfere with ESIPT and with infrared (IR) spectroscopy. Accordingly, we successfully synthesized a broad palette of such variations. Theoretical simulations initially focused on smaller model systems to verify the employed methods and to investigate the basic mechanistic steps. Using a well-established direct dynamics approach with semiempirical configuration-interaction, however, we could also demonstrate already that the full ESIPT-crane-ESIPT sequence shown above is in fact happening in this very system. Using femtosecond UV-vis transient electronic absorption spectroscopy (TEAS), clear indications for ultrafast processes in several of these new ESIPT/crane systems could be obtained.

Beyond the above hydroxyquinoline-derived systems with different proton donor, acceptor and crane stations, we successfully established sequential excited-state proton transfer mechanisms in N-(3-pyridinyl)-2-pyridine-carboxamide (N3PPCA) and N-(2-pyridinyl)-2-pyridine-carboxamide (N2PPCA) by means of transient vibrational absorption spectroscopy (TVAS). Compared to the usually broad and structureless electronic absorption bands seen by TEAS, TVAS offers the advantage of chemical specificity. The observed vibrational features are usually assignable with help from quantum chemical calculations. N3PPCA showcases a fifth and a sixth proton transfer stationcompared to N2PPCA. Last but not least, new TVAS results have shown intermolecular excited-state proton and double-proton transfer in H-bonded 2-aminopurine-thymine base pairsin Watson-Crick-and Hoogsteen conformations.

All cells are covered by a sweet molecular layer of particular complexity, dimension and biological significance. This extracellular compartment is called a cell’s glycocalyx. Molecular recognition of glycocalyx constituents such as glycoconjugates and their interaction with specialized proteins are fundamental to cell biology. An important part in the orchestration of carbohydrate recognition on the cell surface is apparently played by relative orientation of sugar epitopes. In order to investigate the relevance of sugar orientation, we have started a program involving sugars & light, to switch carbohydrate orientation on surfaces, such as for the control of bacterial adhesion. We have additionally commenced a project dedicated to the synthesis and testing of “pseudoenantiomeric glycoclusters” to investigate the significance of carbohydrate orientation in carbohydrate recognition. For the biological evaluation we are employing the mannose-specific adhesion of type 1-fimbriated Escherichia coli.

Visible light is a fascinating reagent: It provides energy for chemical trans­formations, can be selectively delivered to a specific molecule and leaves no trace even if applied in large excess. The three typically classes of photo­chromic molecules in decreasing order of their use are azobenzenes,1 dithienylethenes and fulgides. Different photoswitches have specific advantages and disadvantages for applications in photopharmacology. We discuss their properties with recent examples from our laboratory aiming at photochromic enzyme inhibitors,2 ligands of G-protein coupled receptors,3 redox mediators4 and ion channel modulators.

Figure 1. Typical photoswitches in photopharmacology

References
1. Simeth, N. A.; Crespi, S.; Fagnoni, M.; König, B. J. Am. Chem. Soc. 2018, 140, 2940.
2. Reisinger, B.; Kuzmanovic, N.; Löffler, P.; Merkl, R.; König, B.; Sterner, R. Angew. Chem. Int. Ed. 2014, 53, 595.
3. Lachmann, D.; Studte, C.; Männel, B.; Hübner, H.; Gmeiner, P.; König, B. Chem. Eur. J. 2017, 23, 13423.
4. Simeth, N. A.; Kneuttinger, A. C.; Sterner, R.; König, B. Chem. Sci. 2017, 8, 6474.
Acknowledgements
We acknowledge financial support of the Deutsche Forschungsgemeinschaft (GRK 1910) and the EraNet project Modulightor.

Molecules composed of a tripodal sulfur-anchored stand in combination with a functional group allow to firmly anchor the molecule in a defined adsorption geometry on Au(111) surfaces lifting the functional group from the surface into the vacuum for observation with the tip of a scanning tunneling molecule. We will summarize our activities on this concept including: (i) molecular cantilevers with functional groups containing electric dipole moments for the realization of molecular switches driven by the electric field in the tunneling junction [1], (ii) molecular motors, in which a freely rotatable functional group can be switched between several states by the action of the tunneling electrons [2], and (iii) preliminary results on electroluminescence from chromophores in the functional group to insulate them from the substrate and to decrease the non-radiative recombination rate. We will discuss advantages and problems of this approach as well as a perspective.

[1] Lukas Gerhard et al., Nature Comm. 8, 14672 (2016).
[2] Jan Homberg et al., Nanoscale 11, 9015 (2019).

abstract not yet available

abstract not yet available

The electric current traversing the junction of a scanning tunneling microscope (STM) may generate a local emission of light. During the last years, we have used this method to study the intrinsic luminescence properties of individual molecules. This work has progressed in two directions. On one side we have used the ability of the STM to manipulate matter with atomic-scale precision to form single-molecule light emitting devices whose color, intensity and bandwidth can be controlled with high precision [1,2,3].

On the other side, we used the STM to generate sub-molecularly resolved fluorescence maps of molecules separated from a metallic surface by a thin insulating layers. Combined with spectral selection and time-correlated measurements, this hyper-resolved fluorescence microscopy approach allowed us to scrutinize the vibronic structure of individual molecule [4], to characterize the photonics properties of charged species [5] and to track the motion of hydrogen atoms within free-based phthalocyanine molecules [6].

Together with other recent reports [7,8], this result constitutes an important step towards photonic measurements with atoms-scale resolution.

Artistic view of a single ZnPc molecule excited with STM

[1] G. Reecht et al., Phys. Rev. Lett. 112, 047403 (2014)
[2] M.C. Chong et al., Phys. Rev. Lett. 116, 036802 (2016)
[3] M.C. Chong et al., Nanoletters 16, 6480 (2016)
[4] B. Doppagne et al., Phys. Rev. Lett. 118, 127401 (2017)
[5] B. Doppagne et al. Science, 361, 251 (2018)
[6] B. Doppagne et al. unpublished
[7] Y. Zhang et al. Nature 531, 623 (2016)
[8] H. Imada et al., Nature 538, 364 (2016)

The surface chemistry of solid state materials plays a crucial role for their electronic properties. For carbon materials the surface chemistry is very rich and can be used to control the properties in a very broad range, i.e. the electron affinity of the surface[1] or the control of charge states of lattice defects[2].

The change from electron withdrawing to donating surface groups influences the charge state of lattice defects close to the surface. Additionally, the band structure of the material is strongly depending on the surface termination. Therefore, the homogeneous and stable surface functionalization with suitable atoms or groups is key for the fabrication of diamond based devices for e.g. photocatalytic or quantum applications.

Here we report on the efficient surface termination of diamond different surface groups. These treatments lead to highly functionalised surfaces that enable the stabilisation of negative charge states of lattice defects as well as the control of the electron affinity of the surface.

Characterisation using e.g. solid-state NMR techniques and Boehm titration have been used to analyse the functionalised materials qualitatively and quantitatively.

This research has received funding from the European Union?s Horizon 2020 Programme (Grant Agreement no. 665085, DIACAT, www.diacat.eu) and Deutsche Forschungsgemeinschaft under grant KR3316/6-2.

References
[1] D. Zhu, J. A. Bandy, S. Li, R. J. Hamers, Surf. Sci. 650, 295 (2016)
[2] S. Cui, E. L. Hu, Appl. Phys. Lett. 103, 051603 (2013)

In the past years, we designed a series of BODIPY-DAE compounds with carboxylic acid anchoring groups,for reversible light modulation of electron-and energy transfer processes on titanium dioxide surfaces.1-3 My talk will present almost pure two-state (OF and CF) investigations, because of nearly quantitative photoisomerization of the new fluorophore-DAE compounds, under UV-and visible light illumination,2,3 opposite to previously studied compoundsfrom our groupwithother DAE substitution patterns and linker designs.3

1. F. Schweighoefer et al., Ultrafast dynamics of differently aligned COOH-DTE-BODIPY conjugates linked to the surface of titanium dioxide, J. Phys.: Condens. Matter, 2018, 30, 054001 (7pp).
2. N. Ziebart, et al., Synthesis and characterization of non-symmetrical photoswitchable DTE(OMe) sensitizers, Tetrahedron, 2018, 74, 5561-5566.
3. N. Ziebart, et al., A photochromic benzothiadiazole‐diarylethene system with tunable On/Off fluorescence modulation, ChemPhotoChem, 2019, 3, 396-402.

To go beyond the binary operationsoffered by photochromic compounds, building multiphotochromes, that is molecules encompassing several photochromic units, is an appealing strategy. Thoughnumerousmultiphotochromes have been synthesized during the last decade, most aresubject to drastic limitations [1]. For instance, in multi-diarylethenes, it is a common outcome that only one of the photochromes is experimentally active [1,2]. As a consequence, conceiving efficient and useful multiphotochromes remains an important challenge, and theoretical tools might be useful to tackle this challenge.In this talk, I will show why multiphotochromes tend to be less reactive than their constitutive parts using a curve-crossing model that is displayed in Figure 1. Indeed, extra crossing points, not present in isolated photochromes, appear in multiphotochromes, hampering the reactivity [3]. I will discuss strategies that can be used to circumvent this limitation [3,4]. Next, using selected examples, I will show that several criteria (structures, energies, topologies of the orbitals and crossing points, etc.) may play a role in thereactivity of multidiarylethenes. Finally, I will show that surface can be used to break the symmetry of the systems and improve or not performances [5-7].

Figure1. Curvecrossing model for a diarylethene dimer.

1. Fihey, A.; Perrier, A.; Browne, W.R.; Jacquemin, D. Chem. Soc. Rev.2015, 44, 3719.
2. Perrier, A.; Maurel, F.; Jacquemin, D. Acc. Chem. Res. 2012, 45, 1173.
3. Lasorne, F.; Fihey, A.; Mendive-Tapida, D.; Jacquemin, D. Chem. Sci. 2015, 6, 5695.
4. Fihey, A.; Jacquemin, D. Chem. Sci. 2015, 6, 3495.
5. Chen, K.J.; Boucher, F.; Jacquemin, D. J. Phys. Chem. C2015, 119, 16860.
6. Belhboub, A.;Boucher, F.; Jacquemin, D. J. Phys. Chem. C2016, 120, 18281.
7.Belhboub, A.;Boucher, F.; Jacquemin, D. J. Mater. Chem. C2017, 5, 1624.

Protein kinases are enzymes that mediate signal transduction in intracellular signal pathways and regulate cell growth and differentiation. Overactivated kinases, however, can lead to uncontrolled cell proliferation and play a crucial role in tumor progression and inflammatory diseases. Therefore, kinases are important drug targets and the development of small molecule kinase inhibitors has become a major field in pharmaceutical research.[1]

In this project, we have developed photoswitchable small molecule kinase inhibitors that can be switched between a bio-active and a bio-inactive configuration by light.

Figure 1. (Left): Superposition of (Z)-diazocine-axitinib (green tube representation) with the ATP binding pocket of VEGFR2 (pdb code 4AG8).[2] In the Z-configuration the diazocine moiety clashes with the protein surface (gray). No binding mode can be found by molecular modeling. (Middle): E/Z-isomerization of diazocine-axitinib. (Right): Calculated binding mode of (E)-diazocine-axitinib with VEGFR2.

As a start, we investigated the photo-induced E/Z-isomerization of the approved kinase inhibitor axitinib that possesses a stilbene-like moiety by chance. We could demonstrate that (E)-axitinib can be activated in vitro almost quantitatively by irradiation with light of 385 nm. However, photoswitching of axitinib in aqueous solutions is irreversible due to a competing [2+2]-cycloaddition.[3]

To obtain reversibly switchable inhibitors, we have synthesized a suite of diazocine-functionalized axitinib derivatives (Figure 1). In the thermodynamically stable Z‑configuration these compounds do not show ac­tivity in an in vitro VEGFR2 kinase assay (IC50 > 10000 nM). However, by irradiation with light (405 nm) the activity can be significantly increased resulting in an IC50 value of 215 nM. The E-isomer can be switched back to the bio-inactive Z-isomer either with visible light (520 nm) or thermally (t1/2 ≈ 6.6 h at 37 °C).

We also applied the photoswitchable inhibitor approach to other classes of kinases including CK1δ and BRAFV600E.[4,5] As photoswitches we used both, classical azobenzenes as well as diazocines.

Reference
1. J. Zhang, P. L. Yang, N. S. Gray, Nat. Rev. Cancer 2009, 9, 28-39.
2. M. McTigue et al., Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 18281-18289.
3. D. Schmidt, T. Rodat et al., ChemMedChem 2018, 13, 2349-2463.
4. M. Schehr, Photochem. Photobiol. Sci. 2019, 18, 1398-1407.
5. M. Hoorens, Eur. J. Med. Chem. 2019, 179, 133-146.

In project A1, experimental ultrafast spectroscopy and theoretical chemistry collaborate to investigate fundamental photo-induced processes of molecular switches, ranging from isolated switchable molecules and molecular assemblies of several chromophores all the way to molecular photoswitches acting in complex environments. The numerous highlights of this project include the following:

Optimized diazocine switches: In the 1st phase of CRC 677, diazocine was recognized as an improved variant of the frequently used azobenzene. Our theoretical photodynamics simulations indicated that flexibilizing the additional C-C bridge in diazocine, e.g., by inserting an oxygen atom into it, would lead to further improvements. The superior photophysical properties of a new oxa-diazocine switch and the pivotal role of a second, chair-like ground-state conformer were confirmed experimentally and serve as successful example for the rational improvement of photoswitchable systems.

Excited-state energy transfer (EET) in photoswitchable systems: The feasibility of sensitized photoswitching by photo-induced EET was studied in a model dyad consisting of a benzimidazole donor fluorophore linked to a photoswitchable naphtopyran acceptor. Our results indicated a fast (2.9 ps), practically quantitative EET from the donor-excited to the acceptor-excited state, which could be modeled successfully by Förster resonance energy transfer (FRET) and resulted in the desired ring opening of the naphtopyran. The obtained insight should aid in the development of devices utilizing FRET for sensitized photoswitching. In another line of research, the UV-initiated ultrafast photodynamics of a photoswitchable spin-crossover iron(II) complex with a photoisomerizable ligand was studied. Here, the desired photoisomerisation of the ligand turned out to be quenched due to a competing ultrafast EET to a metal-to-ligand charge-transfer (MLCT) state. To create magnetically bistable systems via this approach, photochromic ligands switchable at wavelengths to the red of the MLCT bands, or metal-ligand systems without MLCT transitions in the UV/Vis region should be used.

Photoswitching in poly(azobenzene-trisiloxane): The ultrafast photo-induced processes of a poly(azobenzene-trisiloxane) with azobenzenes as photoswitchable units in the main chain connected by trisiloxane linkers were studied in detail. The results suggest that the isomerisation of the main-chain azobenzene units occurs essentially unhindered via reaction pathways conforming to the accepted scenario for azobenzene in solution. This explains the observed unusually efficient and reversible photoisomerisation of the main-chain poly(azobenzene-trisiloxane), and emphasizes its potential as a new photo-responsive material with high switching amplitude.

Transport by photoswitchable molecular cilia: From the inception of CRC 677, a guiding vision was to create artificial cilia with photoswitchable molecular motors, attached to a surface via TATA platforms (project B9), and to use them as drivers of particle transport at the nanoscale. With our theoretical simulations, we could contribute to understanding how TATA platforms form regular adlayers on surfaces and we could demonstrate actual transport, with QM/MM simulations of a full cilium setup (TATA platform, diazocine motor, tail, transport target).

Organic light emitting diodes (OLEDs) based on electroluminescent conjugated polymers are considered as a promising alternative for display and lighting applications, mainly due to their better compatibility with low-cost production techniques and large substrates. A challenge is multiple-layer deposition to improve the efficiency of the devices and, as a result, their lifetime.

This lecture introduces recent trends in the field of OLED with an emphasis on solution-processed devices. We have in the past developed photochemically crosslinkable semiconductors for fabrication of complex multilayer OLED [1] with a potential for eventually becoming organic lasers [2] and RGB-pixelation. [3,4] Recently, we also introduced organic memories (OMEM) with multi-bit storage capacity.[5,6]

[1] C.D. Müller, A. Falcou, N. Reckefuss, M. Rojahn, V. Wiederhirn, P. Rudati, H. Frohne, O. Nuyken, H. Becker, K. Meerholz, Nature421, 829 (2003).
[2] B.H. Wallikewitz, M. de la Rosa, J.H.W.M. Kremer, D. Hertel, K. Meerholz, Adv. Mat., 22, 531 (2010).
[3] M.C. Gather, A. Köhnen, A. Falcou, H. Becker, Klaus Meerholz, Adv. Funct. Mat. 17, 191 (2007).
[4] F. Ventsch, M.C. Gather, K. Meerholz, Org. Electronics 11, 57 (2010).
[5] P. Zacharias, M. C. Gather, A. Köhnen, N. Rehmann, K. Meerholz, Angew. Chem. Int Ed. 48, 4038 (2009).
[6] R.C. Shallcross, P.O. Körner, E. Maibach, A. Köhnen, K. Meerholz, Adv. Mat. 34, 4807 (2013).

The association of ligands with nucleic acids is an important process in biology and in medicine, because it usually induces a significant change of the DNA structure. As a result, the formation of ligand-DNA complexes may have a fundamental influence on the physiological function of the nucleic acid, so that DNA binders are traditionally considered as potential lead structures in anti-cancer approaches.1 In this context, it is desirable to accomplish spatial and temporal control of the ligand-DNA interaction in order to increase the selectivity and efficiency. For that purpose, the application of light to trigger the DNA-binding event offers several distinct advantages, because lightis non-invasive, traceless, and easy to apply. Indeed, specifically modified photochromic ligands have been reported that bind to DNA with only one of the components of the photochromic equilibrium, so that the association with DNA may be controlled by light.2 In our efforts to assess the structural parameters that govern the association of cationic azoniahetarenes with nucleic acids3 we also examined concepts to accomplish a photo-induced complexation of photoactive substrates.4 Specifically, we applied electrocyclization reactions of spirooxazines, chromenes and styrylpyridines as well as reversible photocycloaddition reactions of styrylquinolizinium and benzo[b]quinolizinium derivatives to generate DNA ligands upon irradiation. In this contribution, the main results of these studies will be presented and discussed with a special emphasis on the trade-off between appropriate photochromic properties and sufficient affinity of the ligand unit toward DNA.

1. S. Neidle, D. E. Thurston, Nat. Rev. Cancer 2005, 5, 285.
2. Representative examples. Spiropyrans: a) J. Andersson, S. Li,P. Lincoln, J. Andréasson, J. Am. Chem. Soc.2008, 130, 11836; b) C. Brieke, A. Heckel, Chem. Eur. J.2013, 19, 15726. Stilbenes: C. G. Fortuna, U. Mazzucato, G. Musumarra, D. Pannacci, A. J. Spalletti, Photochem. Photobiol. A2010, 216, 66. Azobenzenes: a) C. Dohno, S.-N. Uno, K. Nakatani, J. Am. Chem. Soc.2007, 129, 11898. b.) A. Basak, D. Mitra, M. Kar, K. Biradha, Chem. Commun. 2008, 3067. c) X. Wang, J. Huang, Y. Zhou, S. Yan, X. Weng, X. Wu, M. Deng, X. Zhou, Angew. Chem.2010, 122, 5433. Dithienylethenes:A. Mammana, G. T. Carroll, J. Areephong, B. L. Feringa, J. Phys. Chem. B2011, 115, 11581.
3. A. Granzhan, H. Ihmels,Synlett 2016, 27, 1775.
4. a) S. V. Paramonov, V. Lokshin, H. Ihmels, O. A. Fedorova, Photochem. Photobiol. Sci. 2011, 10, 1279. b) H. Ihmels, J. Mattay, F. May, L. Thomas, Org. Biomol. Chem. 2013, 11, 5184. c) D. V. Berdnikova, T. M. Aliyeu, T. Paululat, Y. V. Fedorov, O. A. Fedorova, H. Ihmels, Chem. Commun. 2015, 51, 4906. d) A. Bergen, S. Rudiuk, M. Morel,T. Le Saux, H. Ihmels, D. Baigl, ACS Nanolett. 2016, 16, 773

Inspired by the process of photosynthesis, we are aiming at the design, synthesis and investigation of a model system of molecular assemblers.

In preliminary work in our research group a light-switchable ditopic receptor was synthesized, which is able to drive the condensation of 4 molecules of monovanadate to a cyclic tetravanadate.[1] This receptor contains two zinc-cyclene units as binding sites for oxoanions and a photoswitchable azobenzene unit.

In order to improve the binding of tetravanadate, two of these receptor molecules are connected via spacer units to form a cage-like structure. Suitable spacers are determined by quantum mechanical calculations. Two diethyl ether linkers for example permit an energetically favorable complexation.

Another class of receptor molecules includes diazocines as photoswitches to achieve a pincer-like motion, reduce the degrees of freedom and improve the force transmission. Moreover diazocines exhibit superior photoswitching properties compared to azobenzene.[2] Furthermore the coordination units for oxoanions are varied.

References
[1] H. Sell, A. Gehl, D. Plaul, F. D. Sönnichsen, C. Schütt, F. Köhler, K. Steinborn, R. Herges, Commun. Chem. 2019, 2, 1-6.
[2] R. Siewertsen, H. Neumann, B. Buchheim-Stehn, R. Herges, C. Näther, F. Renth, R. Temps, J. Am. Chem. Soc. 2009, 131, 43, 15594-15595.

Oligothiophenes represent an important class of compounds in the field of organic semiconductors and or­ga­nic electronics. On the basis of thiophenes, we are currently synthesizing and investigating novel conjugated architectures and shapes, such as linear, macrocyclic, dendritic, or fused.

In particular, we have recently developed series of novel S,N-heteroacenes up to a 13-mer which com­bine the sta­bility of oligothiophenes and the planar extended -system of (phen)acenes.1 Con­ju­gated materials with highly interesting opto­elec­­tro­nic properties,2 small bond length alternation, pla­na­rity, and good charge transport properties qualify them for application in hig­hly efficient organic3 and perovskite solar cells.4 This class of compounds has now been extended to corresponding sele­no­­phene and silole-containing heteroacenes.

Opposite to the flat heteroacenic structures, we started to develop and synthesize three-dimen­sio­nal and sterically crow­ded thienylene-phenylene structures.

1. C. Wetzel, E. Brier, A. Vogt, A. Mishra, E. Mena-Osteritz, P. Bäuerle, Angew. Chem. Int. Ed. 2015, 54, 12334;
2. C. Wetzel, A. Vogt, A. Rudnick, E. Mena-Osteritz, A. Köhler, P. Bäuerle, Org. Chem. Front. 2017, 4, 1629-1635;
3. T. Leitner, A. Vogt, D. Popović, E. Mena-Osteritz, K. Walzer, M. Pfeiffer, P. Bäuerle, Mater. Chem. Front., 2018, 2, 959-968;
4. D. Bi, A. Mishra, P. Gao, M. Franckevicius, C. Steck, S. M. Zakeeruddin, M. K. Nazeeruddin, P. Bäuerle, M. Grätzel, A. Hagfeldt, ChemSusChem, 2016, 9, 433-438.

abstract not yet available

Indigoid chormophores are a class of emerging photoswitches with many advantages for applications. However, despite their high potential as versatile and efficient molecular triggering unit, they have been largely overlooked by material sciences as well as supramolecular and biological chemistry. In the recent years, we have explored the interesting photophysical properties of indigoid photoswitches in depth and developed a thorough mechanistic understanding of their light induced motions and behavior in the excited state. We use this fundamental knowledge to build next generation molecular machines and responsive supramolecular systems with unprecedented properties. Our main goal is to develop smart molecular entities, which can conveniently be implemented into more complex architectures to manipulate matter at the molecular scale with the highest possible precision.

Controlled attachment of various molecular machines (motors, rotors, and switches) to flat surfaces is an attractive and promising route towards new generation of highly ordered 2‑D materials. Organization of individual molecules into regular arrays (Figure 1) should among others amplify their function and lead to the new types of smart materials with potential application for example in nanoelectronics. Several approaches leading to such systems built on solid-gas1,2 and liquid-gas3,4 interphases will be discussed.

Figure 1: Regular array of molecular motors (left) and rotors (right).

[1] Kaleta, J.; Dron, P. I.; Zhao, K.; Shen, Y.; Císařová, I.; Rogers, C. T.; Michl, J. J. Org. Chem. 2015, 80, 6173-6192.
[2] Kaleta, J.; Chen, J.; Bastien, G.; Dračínský, M.; Mašát, M.; Rogers, C. T.; Feringa, B. L.; Michl, J. J. Am. Chem. Soc. 2017, 139, 10486-10498.
[3] Kaleta, J.; Kaletová, E.; Císařová, I.; Teat, S. J.; Michl, J. J. Org. Chem. 2015, 80, 10134-10150.
[4] Kaleta, J.; Wen, J.; Magnera, T. F.; Dron, P. I.; Zhu, C.; Michl, J. PNAS 2018, 115, 9373-9378.

abstract not yet available

Molecular electronics aims at utilizing functional molecules as building blocks of electronic components. In that respect, molecules adsorbed on a surface exhibitingaspin switching functionality are particularly interesting. Molecules possessing different properties were deposited on metallic surfaces using two different techniques: sublimation for the most robust molecules and electrospray depositionfor the more fragile molecules. The adsorption, along with the electronic and magnetic properties of the deposited molecules, were investigated using low-temperature scanning tunneling microscopyandspectroscopyalong with x-ray absorption spectroscopy. The molecules were switched usingdifferent triggers, e.g.,electrons, coordinationofaxialligands, contact with the STM tip.This resultsin various changes of the molecular properties such as theiradsorption properties [1] and theirelectronicand magneticproperties [2-4]. A strong emphasis will be given on the investigation of so-called hairclip complexes, a new class of molecules where coordination and spin switchingare interlocked [5]. Furthermore, it will be shown that magnetism can be induced and controlled in non-magnetic molecule through controlled supramolecular manipulations[6].

References:
[1] A surface ciseffect: Influence of an axial ligand on molecular self-assembly.
Th. Knaak, T. G. Gopakumar, B. Schwager, F. Tuczek, R. Robles, N. Lorente, R. Berndt, J.Am. Chem. Soc. 2016, 138, 7544 –7550.
[2] Deposition of a cationic Fe(III) spin-crossover complex on Au(111): Impact of thecounter ion.
T. Jasper-Tönnies, M. Gruber, S. Karan, H. Jacob, F. Tuczek, R. Berndt, J. Phys. Chem. Lett. 2017, 8, 1569 –1573.
[3] Robust and selective switching of a Fe(III) spin-crossovercompound on Cu2N/Cu(100) with memristance behavior.
T. Jasper-Tönnies, M. Gruber, S. Karan, H. Jacob, F. Tuczek, R. Berndt, Nano Lett. 2017, 17, 6613 –6619.
[4] Spin control induced by molecular charging in a transport junction.
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The mechanical and dynamic properties of phospholipid membranes are of importance for biological functions, such as switching of embedded proteins and cell transport. In order to investigate these properties we study model systems in which amphiphilic photoswitchable molecules are integrated into Langmuir films of phospholipids. We have modified glycolipids to contain an azobenzene photoswitch between the chain and the head groupand successfully embedded those in a monolayer of dipalmitoylphosphatidylcholine (DPPC)[1]. This allows us to reversibly change the azobenzene-glycolipid orientation between trans-and cis-conformation by illumination with UV and blue light. We investigated the switching behavior with Langmuir isotherms and observed an additional phase transition compared to DPPC monolayer. Additionally we have followed the structural changes in this model membrane and the switching kinetics of the system with in situ X-ray reflectivity and Gracing Incident Diffraction at the LISA diffractometer P08, PETRA III[2]. Strong changes in membrane conformation upon switching have been observed.

[1] F. Reise et al., Chem. Eur. J. 17497-17505 (2018)
[2] B. M. Murphy et al., J. Syn. Rad. 45-56 (2014) 21

abstract not yet available

Ni(II)porphyrins can be switched between a diamagnetic and paramagnetic state at room temperature by light-driven coordination-induced spin state switch (LD-CISSS). Switching of the coordination number and subsequently of the spin state is achieved by using Ni(II)porphyrin as a square planar platform and azopyridine or azoimidazole as a photoswitchable axial ligand that is bonded covalently at one meso position of the porphyrin. The square planar Ni(II)porphyrin of the so called record player molecule is diamagnetic (low-spin, S = 0) while the square pyramidal complex is paramagnetic (high-spin, S = 1). The switching process can be controlled by irradiation with light of different wavelengths. The photoswitchable azopyridine only binds in the cis configuration and dissociates in the trans form. This LD-CISSS is a novel approach for the design of light responsive MRI contrast agents (scheme 1).[1-5]

In the last funding period we were focused on solving a number of problems prior to applications in vivo:
1. introducing water solubility, switching in water and human serum[5,6]
2. shifting the wavelengths of the switching process to the bio optical window (650- 850 nm)[6,7]
3. synthesis of smart contrast agents that are sensitive to physiological parameters (temperature, pH)[6,8,9]
4.developing MR sequences for determination of relaxation times as well as the measurement of switching kinetics with high temporal and spatial resolution[10]

Literature:
[1] S. Thies et al., J. Am. Chem. Soc. 2011, 133, 16243-16250;
[2] S. Venkataramani et al., Science 2011, 331, 445-448;
[3] S. Thies et al., Chem. Eur. J. 2012, 18, 16358-16368.;
[4] M. Dommaschk et al., J. Am. Chem. Soc. 2015, 137, 7552-7555;
[5] M. Dommaschk Dissertation, CAUKiel 2016;
[6] V. Wellm, current work, CAUKiel 2019;
[7] M. Dommaschk, V. Thoms et al., Inorg. Chem. 2015, 54, 9390-9392;
[8] G. Heitmann, unpublished results, CAU Kiel 2016;
[9] J. Ludwig, current work, CAU Kiel 2019;
[10] J. Groebner, current work, CAU Kiel 2019.

Scanning tunneling microscopy (STM) is a key experimental technique to address individual molecules on surfaces and to probe their structural, electronic, and magnetic properties. It is even possible to switch a molecular state by applying current pulses, electric fields, or by direct interaction with the STM tip. The forces between molecule and tip can be measured by atomic force microscopy (AFM). Microscopes which combine both STM and AFM allow to measure conductance and force curves simultaneously. With magnetic tips this technique can be made spin sensitive allowing to measure both spin-polarized currents and exchange forces as recently demonstrated [1]. However, the interpretation of such experiments is often non-trivial and first-principles calculations based on density functional theory (DFT) have become an indispensable theoretical tool.

Here, I will show how we can understand the tip-molecule interaction and the conductance in STM/AFM measurements on SnPc molecules on a Ag(111) surface [2] based on DFT. The conductance as a function of tip-molecule separation exhibits an exponential dependence with similar decay length for the two possible configurations. However, the short-range forces between tip and molecule display a non-trivial distance dependence distinctively different from those of single-atom contacts as shown by DFT. Therefore, molecule deformations occur which lead to the unexpected force curves. Quantitative spin-sensitive STM/AFM measurements have recently been performed for a Mn monolayer on W(110) [3] which exhibits a cycloidal spin spiral. This surface is ideally suited to study single magnetic atoms or molecules as their spin quantization axis can be rotated quasi continuously by exchange coupling to the spin spiral [4-6]. Our DFT calculations reveal that the measured atomic-scale variations in the exchange force on Mn/W(110) originate from different contributions of direct and indirect exchange mechanisms depending on the chemical tip termination [3].

[1] N. Hauptmann, J. Gerritsen, D. Wegner, and A. A. Khajetoorians, Nano Lett. 17, 5660 (2017).
[2] N.M. Caffrey, K. Buchmann, N. Hauptmann, C. Lazo, P. Ferriani, S. Heinze and R. Berndt, Nano Lett. 15, 5156 (2015).
[3] N. Hauptmann, S. Haldar, T.-C. Hung, W. Jolie, M. Gutzeit, D. Wegner, S. Heinze, and A. A. Khajetoorians, in preparation.
[4] D. Serrate, P. Ferriani, Y. Yoshida, S.-W. Hla, M. Menzel, K. von Bergmann, S. Heinze, A. Kubetzka, and R. Wiesendanger, Nat. Nanotechnol. 5, 350 (2010).
[5] N. M. Caffrey, P. Ferriani, S. Marocchi, and S. Heinze, Phys. Rev. B 88, 155403 (2013).
[6] S. Haldar and S. Heinze, Phys. Rev. B 98, 220401 (R) (2018).

Whether or not an object has a superimposable mirror image is formally a binary issue. However, it is the extent to which chirality is expressed on the space surrounding a molecular structure that is generally important for the effective transmission of asymmetry. This work reports rotaxane organocatalysts whose chiral expression is controlled by shuttling of the macrocycle. The process can be exploited to enhance the effective asymmetry and to change the apparent handedness of the environment around a catalytic site. It is the first example for the dynamic control of the facial bias in organocatalysis using a rotaxane.