We will present recent results concerning ultrafast intramolecular relaxation processes in metal-based molecular complexes, involving changes of spin and structure. Using a broad range of ultrafast optical and X-ray tools we present studies of the ultrafast electronic/vibrational relaxation at sub-vibrational time scales, ultrafast intersystem crossing processes and ultrafast structure changes. We will stress the points that allow a rationale to be developed, that describes these processes. The systems we investigate consist of Fe, Ru, Re, Pt and Cu complexes in solutions.

The development of rational design strategies for optimized photochromic molecular switches requires detailed knowledge about the dynamics of the ensuing ultrafast photo-induced chemical transformations and the competing radiationless electronic deactivation processes that determine the switching efficiencies and the quantum yields. Moreover, the application potential of the photoswitches as tiny light-driven switches, manipulators, actuators or memories depends critically on how the surrounding matrix affects the photo-induced transformations. In order to elucidate these topics, we have investigated the influences of severe intramolecular or intermolecular constraints on the dynamics of selected photoswitches in solution and in polymeric micronetworks. For a diazocine (an azobenzene derivative with an eight-membered ring) and for a set of furylfulgides, we observed strongly accelerated photoreactions in only ≈ 50 fs by intramolecular constraints leading to directed movement on the excited-state potential energy hypersurfaces to the conical intersection regions that control the molecular transformations. Strong intermolecular mechanical forces, on the other hand, acting on a cross-linked trans-azobenzene switch in the main-chain of a polybutyl­meth­acrylate matrix were found to impede the photoreaction (τ ≈ 180 ps). In multi-azobenzene compounds, we have observed strong chromophore-chromophore interactions and electronic coupling between two resp. three addressable azobenzene units connected by a central nitrogen atom. The talk will give an overview over recent results obtained in the SFB.

The 2D coordination network [Fe(bbtr)₃](ClO₄)₂ (bbtr = 1,4-di(1,2,3-triazol-1-yl)butane) is known for its abrupt high-spin (HS) ⇔ low-spin (LS) transition at around 100 K and a thermal hysteresis of 13 K due to an accompanying crystallographic phase transition. [1] In the corresponding dilute mixed system [Zn_1-xFe_x(bbtr)₃](ClO₄)2 (x = 0.02), the iron(II) centres stay essentially in the HS state down to 10 K. For increasing values of x, the LS fraction at 10 K increases. We report the HS⇔LS relaxation dynamics over a wide temperature range using wavelength selective excitation for the light-induced population of the LS state through irradiation in the near IR. Thus for instance for x = 0.02, the LS→HS relaxation rate constant increases by 14 orders of magnitude, [2,3] that is, from less than 5x10^-7 s^-1 (τ = 25 days) below 40 K to 3x10⁷ s^-1 (τ = 30 ns) at 220 K.

On the other hand, the neat BF4 - analogue stays in the HS state down to 10 K (see Fig. 1). It can, however, be quantitatively converted to the LS state by irradiating into the near-IR spin allowed 5 dd band and back again by irradiating into the visible 1 dd band. Depending upon the initial light-induced LS/HS ratio the system either returns to the HS state or goes fully to the LS state. In the latter case it only returns to the HS state above 100 K. Therefore, it shows true light induced bistability below 100K, [4] thus having the potential for persistent bidirectional optical switching at elevated temperatures. This behaviour is attributed to strong cooperative effects of elastic origin.

The variation of elastic interactions and the study of the dynamics in [Zn1-xFex(bbtr)₃](ClO₄)₂ mixed crystals as well as in the BF₄ - derivative using LIESST and reverse-LIESST could thus help to design highly cooperative systems for memory devices.

Figure 1: The HS fraction as function of temperature: on cooling from room temperature down to 10 K at a rate of 0.2 K/min (black dots), after irradiation at 12050 cm^-1 at 10 K to the steady state high-spin fraction of 15% and subsequent warming to 120 K at a rate of 0.2 K/min (red dots) or stopping at 60 K and recooling to 10 K (yellow dots), after a short irradiation time at 12050 cm^-1 and10 K resulting in an initial high-spin fraction of 85% and subsequent warming to 120 K at a rate of 0.2 K/min (green dots)

[1] I. Krivokapic, C. Enachescu, R. Bronisz, and A. Hauser, Chem. Phys. Lett. 2008, 455, 192.
[2] I. Krivokapic, P. Chakraborty, C. Enachescu, R. Bronisz and A. Hauser, Angew. Chem. Int. Ed. 2010, 49, 8509.
[3] I. Krivokapic, P. Chakraborty, C. Enachescu, R. Bronisz and A. Hauser, Inorg. Chem. 2011, 50, 1856.
[4] P. Chakraborty, R. Bronisz, C. Besnard, L. Guénée, P. Pattison, A. Hauser, J. Am. Chem. Soc. 134 (2012) 4049.

Electron transport through single molecule contacts is the basis of designing molecular electronics and is capable of inducing switching processes. To understand the geometry of the junction that underlies its transport properties, the forces arising during conductance measurements in such contacts are important. We use low-temperature scanning tunneling and atomic force microscopy to simultaneously measure the force and conductance in single molecule contacts and show that the detailed electrode geometry and molecular structure strongly affect the conductance.

Magnetic properties such as magnetic bistability (e.g. magnetization in ferromagnetic materials) are solid state properties. Numerous attempts notwithstanding, (mainly with miniaturization of magnetic storage media in mind) switchable magnetic systems are either restricted to very low temperatures (~4K) or to solid state materials. We present the first system which is bistable as an isolated molecule at room temperature. The operating principle is based on the fact that some transition metals are either dia- or paramagnetic depending on their coordination number. We designed and synthesized a molecular machine-like transition metal complex whose coordination number, and hence whose magnetic state can be reversibly switched by irradiation with green and blue light. Potential applications are smart contrast agents for magnetic resonance imaging (MRI), switchable spin labelling for NMR, and light-controlled magnetic levitation.

1. 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.
2. 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.

Changes in color, magnetic moment, electrical conductivity or occupied volume are only a view of the fascinating properties of switchable molecules. These properties inspire to transfer them into applications with macroscopically visible effects. Often, this is a challenge for the used materials and requires new developments of material solutions that allow the integration of switchable molecules. Mainly on the example of the development of a bioinspired light switchable dry adhesive material the challenges and novel material solutions will be introduced. These include novel concepts to join mostly unjoinable polymers like PDMS (Silicone) and PTFE (Teflon) and ultralightweight materials like the recently developed Aerographite which is currently the least dense material.

Merging the concepts of molecular electronics with spintronics opens one of the most exciting avenue in designing and building future nanoelectronic devices. The ability to reliably describe the electronic properties of molecules adsorbed on magnetic surfaces is essential to understand and design the functionality of hybrid organic molecular devices. This strongly depends on the accuracy of the state-of-theart theoretical methods used to assess the interaction between a molecule or a molecular layer and a substrate of choice. Our theoretical studies [1-6] show that, with its predictive power, the density functional theory (DFT) provides a framework where a realistic description of these hybrid systems can be expected and can be further used to tune both the electronic and magnetic properties at hybrid organometallic interfaces. Besides this, our studies demonstrate the decisive role played by the van der Waals forces in correctly describing the interaction between aromatic molecules and metallic surfaces.

I will present conceptual studies performed to understand how to tailor the magnetic properties at a hybrid organic-ferromagnetic interface by adsorbing organic molecules containing π-electrons onto a magnetic substrate. For such hybrid systems, the magnetic properties like molecular magnetic moments and their spatial orientation can be specifically tuned by an appropriate choice of the chemical substituents. Our ab initio calculations demonstrate that, by employing an appropriate chemical functionalization of organic molecules adsorbed on a ferromagnetic surface, a fine tuning of the spin-unbalanced electronic structure can be achieved. For example, by using molecular substituents with different electronegativities attached to π- conjugated systems adsorbed on a ferromagnetic surface, the electrons with a specific spin [i.e. up (↑) and down (↓)] can selectively be injected at the molecular site from the same ferromagnetic substrate. Even more important, we show that there is direct correspondence between the substituent’s electronegativity and the size of the induced molecular magnetic moment. As regarding the stability of the magnetization direction of the hybrid organic-ferromagnetic system, we demonstrate that the adsorbed hydrogenated molecules destabilize more the out-of-plane magnetization of the ferromagnetic surface as compared to molecules containing more electronegative atoms as Cl and F which could also enhance it. Ultimately, this allows us to precisely engineer the magnetic properties of the hybrid organic-ferromagnetic interfaces which can be further exploited to design more efficient spintronic devices based on organic molecules.

References:
[1] N. Atodiresei, P. H. Dederichs, Y. Mokrousov, L. Bergqvist, G. Bihlmayer, S. Blügel, Phys. Rev. Lett. 100, 117207 (2008)
[2] N. Atodiresei, V. Caciuc, P. Lazic, S. Blügel, Phys. Rev. Lett. 102, 136809 (2009)
[3] N. Atodiresei, J. Brede, P. Lazic, V. Caciuc, G. Hoffmann, R. Wiesendanger, S. Blügel, Phys. Rev. Lett. 105, 066601 (2010)
[4] J. Brede, N. Atodiresei, S. Kuck, P. Lazic, V. Caciuc, Y. Morikawa, G. Hoffmann, S. Blügel, R. Wiesendanger, Phys. Rev. Lett. 105, 047204 (2010)
[5] C. Busse, P. Lazic, R. Djemour, J. Coraux, T. Gerber, N. Atodiresei, V. Caciuc, R. Brako, A. T. N'Diaye, S. Blügel, J. Zegenhagen, T. Michely, Phys. Rev. Lett. 107, 036101 (2011)
[6] N. Atodiresei, V. Caciuc, P. Lazic, S. Blügel, Phys. Rev. B 84, 172402 (2011)

The π-electrons of the cobalt-phthalocyanine molecule hybridize strong with the d-electrons of a magnetic metal and, as a consequence, a complex energy dependent magnetic structure is formed. Therefore, near the Fermi level, at the molecular site an inversion of the spin-polarization with respect to the ferromagnetic surface occurs. Our studies demonstrate that electrons of different spin [i.e. up (↑) and down (↓)] can selectively be injected from the same ferromagnetic surface by locally controlling the inversion of the spinpolarization.

For use as motor units in any conceivable application, photochemically switching molecules have to show very specific properties. A rational design process of these properties requires a detailed unterstanding of the underlying ultrafast dynamical processes. This can only be achieved by close co-operation of experimental and theoretical investigations. Therefore, the Hartke group complements the state-of-the-art experimental work in SFB677 with high-end theoretical investigations. These include highly accurate multi-referential ab-initio electronic structure methods combined with direct dynamics simulations of the molecules of interest.

This talk will highlight examples of recent work in our group: Furylfulgides can act as molecular switches via interconversion between their E- and C-forms, by photochemically induced electrocyclic ring opening/closure at the central system of 6 pi-electrons. This interconversion is perturbed by the ability of the E-form to also interconvert to the Z-form. Additionally, all of these photochemical steps can either successfully form their respec- tive products or lead back to the reactants. In experiments, a strong sensitivity of this photochemical reaction network to seemingly minor substituent changes was found. Our theoretical investigations uncovered an intricate balance between the desired ”concerted” reaction of all 6 pi-electrons as a single chromophor and ”individual” photochemical steps of only 2 pi-electrons acting as in an ethylenic chromophor [1]. This balance is changed substantially by small alterations in the substituent pattern. Additionally, this picture is complicated further by the Z-form exhibiting electronic characteristics that differ from that of the E- and C-forms. Again, evidence for this may be visible in the experimental findings.

Current work focuses on coupled multi-chromophoric azobenzene-based systems. Simu- lations of static UV-spectra are in good agreement with experiment. Initial studies of a detailed balance between the individual chromophors acting on their own or as a strongly coupled, larger chromophor, will be presented in the talk.

References
[1] J. B. Sch ̈ onborn, A. Koslowski, W. Thiel, and B. Hartke. Phys. Chem. Chem. Phys., 2012. in press.

Smart materials that react to a stimulus or their environment to produce a dynamic and reversible change in decisive properties are drawn the attention recently. Photochromic molecule is one of those materials which can turn any composite system into smart materials provided the host matrix is soft enough (e.g. polymer) to let the molecule rotate upon illumination. The exclusive properties of these molecules can be even more advantageous once it is integrated onto the devices whose optical properties are the matter of interest (e.g. plasmonic devices) and make them smart.

Here we highlight our recent works on optoelectronic devices that explore the interaction of plasmon resonance of the metals and dipoles, i.e. nanoparticles, molecules [1-4]. As specific highlight we introduce the first photoswitchable transparent conducting metal composed of Spirophenanthrooxazine (SPO) molecules and metallic film [5].

1. M. Elbahri, M.K. Hedayati, F. Faupel, T. Strunkus, V. Zaporojtchenko, V.S.K. Chakravanadhanula, “Metall-Komposit-Beschichtung mit hoher optischer Transmissivität im visuellen Spektrumpatent,” DE 102010050110.7 (Patent pending).
2. M. Elbahri, M.K. Hedayati, V.S.K. Chakravanadhanula, M. Jamali, T. Strunkus, V. Zaporojtchenko, F. Faupel, Adv. Mater., Vol. 23, 1993-1997, 2011.
3. M. Elbahri, M.K. Hedayati, F. Faupel, T. Strunkus, V. Zaporojtchenko, “Absorberschicht für den VIS- und/oder NIR-Spektralbereich, ” DE 10 2011 113 571.9 (Patent pending).
4. M. K. Hedayati, M. Javaherirahim, B. Mozooni, R. Abdelaziz, A. Tavassolizadeh, V. S. K. Chakravadhanula, V. Zaporojtchenko, T. Strunkus, F. Faupel, M. Elbahri, Adv. Mater. 23, 5410–5414 (2011).
5. M. Jamali, M.K. Hedayati, B. Mozooni, M. Javaherirahim, R. Abdelaziz, A.U. Zillohu, M. Elbahri, Adv. Mater., Vol. 23, 4243-4247, 2011.

Julia Bahrenburg
Ultrafast Dynamics of Molecular Photoswitches by Femtosecond Spectroscopy
show abstract

Vijayanand Chandrasekaran
Switchable cell adhesion by azobenzene glycosides
show abstract

Marcel Dommaschk
Switchable cell adhesion by azobenzene glycosides
show abstract

Lars Heepe
Microscopic detachment behavior of mushroom-shaped adhesive microstructure at 180000 fps
show abstract

Gernot Heitmann
Intramolecular LD-CISSS in azoimidazole-functionalized Nickel(II)porphyrins for development of photoswitchable MRI contrast agents
show abstract

Michelle Holz
Photoswitchable Monolayers: A Dynamic Control over Cell Adhesion
show abstract

Hanne Jacob, Sven Olaf Schmidt
Iron-complexes for spin switching in solution, fixation on gold and in thin films
show abstract

Laith Kadem
Nanostructured surfaces as platforms for photoswitchable cell adhesion
show abstract

Emre Kizilkan
Underwater Adhesion of Mushroom Shaped Adhesive Microstructure: An Air-Entrapment Effect
show abstract

Hauke Kobarg, Anne Müller
Photoswitchable Antifreeze Proteins
show abstract

Isabel Köhl
Molecular switches for AFM measurements
show abstract

Anja Köhntopp
Photoswitching Properties of Azobenzene-Functionalized Gold Nanoparticles
show abstract

Sonja Kuhn
In situ STM Investigations of Platform Adlayers on Au(111) Surfaces
show abstract

Matthias Müller
Photoisomerization of Azobenzene-Functionalized Alkanethiols and Platform Adlayers on Au
show abstract

Lina Sophie Noll, Bettina Schwager
Iron-complexes as a switchable MRI-contrast-agent
show abstract

Julia Reverey
Investigation and biomimicry of target cell killing by Acanthamoeba
show abstract

Saira Riaz
Studying the Morphology of Azobenzene Containing Mixed Monolayers on Gold by VSFG Spectroscopy
show abstract

Benjamin Sahlmann
Synthesis of Photoswitchable Ligands for Metal Ions Based on the Norbornadiene-Quadricyclane-System
show abstract

Christian Schütt
Light-Driven-Coordination Induced Spin-State Switch: Rational Design of Photodissociable Ligands using Density Functional Theory Methods
show abstract

Doreen Schütze
Single molecule force-clamp spectroscopy on azobenzene monomers linking PEG spacers
show abstract

Stefan Schwarzer
Subject matter education support of the SFB 677
show abstract

Jan Strüben, Xin Jin
Tetrapodal ZnO Microparticles as Powerful Linkers Between Low Surface Energy Polymers
show abstract

Photochromic molecules are able to translate an incoming light stimulus into property changes of a given material, thereby allowing to control and even power its function in a specific process. The exquisite spatio-temporal control provided by the light input has sparked a considerable interest in such photoswitchable systems with potential application ranging from ”smart” surfaces and polymers[1] over remote-controlled catalysts[2] to light-driven actuators.[3] The interface between the light stimulus and the material is provided by a photosensitive gate – the photochromic unit. While a lot of effort recently has been devoted towards incorporating such photoswitchable gates into macro- and supramolecules and organic-inorganic hybrid materials as well as decorating surfaces, fundamental research to develop and improve photochromic systems remains important. In this lecture, the most recent progress by our group as well as others on improving the switching performance of azobenzene as well as diarylethene photochromes will be described.

References
[1] M.-M. Russew, S. Hecht, Adv. Mater. 2010, 22, 22, 3348-3360.
[2] R. S. Stoll, S. Hecht, Angew. Chem. Int. Ed. 2010, 49, 5054-5075.
[3] D. Bléger, Z. Yu, S. Hecht, Chem. Commun. 2011, 47, 12260-12266.

Transmembrane receptors allow a cell to communicate with its environment in response to a variety of input signals. These can be changes in the concentration of ligands (e.g. hormones or neurotransmitters), temperature, pressure (e.g. via acoustic waves or touch), transmembrane potential, or light intensity. Many important receptors have now been characterized in atomic detail and our understanding of their functional properties has markedly increased in recent years. As a consequence, these sophisticated molecular machines can be reprogrammed to respond to unnatural input signals. Arguably, the most useful of these signals is light. I will show how ligand-gated ion channels, G-protein coupled receptors, as well as voltage-gated ion channels, can be manipulated with synthetic photoswitches to become light-sensitive. The resulting hybrid photoreceptors can be used to optically control neurons with very high precision. They have been used to dissect neural networks and might find applications in the restoration of vision and the control of other sensations (such as pain). This combination of synthetic photoswitches and receptor proteins augments the field of Optogenetics and adds a new functional dimension to Chemical Genetics. As such, we propose to call it “Optochemical Genetics”.

The fabrication of high performance integrated circuits provides examples of the most sophisticated manufacturing methods, as well as the most high performance materials, used in an area of modern technology. The advanced functional systems they provide are ones that are generally characterized by a massive integration of circuit elements within compact, rigid and essentially planar form factor devices. New means of fabrication and enabling materials are beginning to provide a set of means through which it is possible to lift some of these latter constraints—doing so in ways that both retain capacities for high performance while enabling new, low cost opportunities for use in technology. Our collaborative research here at the University of Illinois is providing form factors for devices with interesting but what had been to date difficult to realize features. Examples include: light weight, large area, high performance electronics, optics, and photonics; electro optical systems with curvilinear shapes and capacities for accommodating demanding forms of mechanical flexure; and hybrid systems for lighting, energy storage, and photovoltaic energy conversion that might provide potentially transformational approaches to supplant current technologies with high performance, low cost alternatives. In this lecture I will explore examples of energy technologies enabled by new form factors for devices and the highly functional surfaces used for their construction.

The extent to which effects emerging at the nanoscale can be exploited is crucially dependent on both the precision at which structures can be controlled and dimensional gaps be bridged. Driven by the limitations of established lithography based approaches, a range of alternative routes is explored to address these issues with concepts involving templating and self-assembly on surfaces playing an important role. The vitually unlimited flexibility in the design of organic molecules in combination with simple processing at the liquid/solid interface make two complementary self-assembly strategies, namely self-assembled monolayers (SAMs) and supramolecular networks (SMNs), appealing components of a toolbox for the nanoscale. SAMs provide unique opportunities for the functionalisation of surfaces and control of interfacial energy but, as part of a top-down approach, their patterning is limited in resolution by the applied lithographic techniques. In contrast, SMNs as prototypical systems for the bottom-up approach provide access to ultraprecise structures on the sub-5 nm scale but are less amenable to chemical functionalisation. Thus, merging both assembly concepts [1] has an obvious potential for the control of interfacial structure and properties on a length scale ultimately down to the level of individual molecules. The scope of SAMs and SMNs is further augmented if combined with electrochemistry as another powerful tool for the nanoscale due to the precise thermodynamic and kinetic control of processes. The talk will discuss various approaches where SAMs and SMNs serve as templates on a length scale ranging from micrometres to the bottom end of the nanoscale. Emphasis will be put on the generation of metal structures by SAM controlled electrodeposition [2] and the use of SMNs as ultraprecise matrix [3].

References:
[1] R. Madueno, M. T. Raisanen, C. Silien, M. Buck, Nature 454, 618 (2008), Functionalizing hydrogen-bonded surface networks with self-assembled monolayers.
[2] Z. She, A. DiFalco, G. Hähner, M. Buck, Beilst. J. Nanotechnol. 3, 101 (2012), Electron-beam patterned self-assembled monolayers as templates for Cu electrodeposition and lift-off. .
[3] M. T. Räisänen, A. G. Slater, N. R. Champness, M. Buck, Chem. Sci. 3, 84 (2012), Effects of pore modification on the templating of guest molecules in a 2D honeycomb network.

Functional surfaces are of particular interest because of future applications (e. g. for data storage devices, lab-on-a-chip, molecular machines, etc.). In many cases, such surfaces are prepared by adsorption and self-organization of appropriate functional molecules from solution on solid substrates. In particular, very often molecules are employed, which bind to a metal via a thiol group. However, such adlayers were typically found to exhibit only a reduced or even completely quenched function, which can be explained by interactions between the substrate and the adsorbate molecules (electronic or excitonic coupling) as well as intermolecular interactions (steric hindrances). Common approaches to overcome these problems employ molecules with additional bulky spacer groups or mixed monolayers with short spacer molecules. Unfortunately, these adlayers often exhibit only a reduced structural order or a tendency to form bilayers. We have introduced a novel concept based on chemically customizable molecular platforms [1,2], which allows to orient molecular functions in a defined manner with respect to the substrate and to precisely control the distance between the surface and the functions as well as the intermolecular distances within the surface plane. In addition, we have extensively characterized adlayers of such compounds on Au(111) surfaces by structure-sensitive (STM) [1,3,4,5], spectroscopy (XPS, SERS, and surface plasmon resonance (SPR) spectroscopy) [4], and electrochemical methods (cyclic voltammetry) [4] and clearly demonstrated that the molecular platforms adsorb intact and form highly-ordered structures.

Here, we discuss the photoswitching of azobenzene-functionalized platform adlayers in detail and compare it to that of conventional adlayers basing on thiols. In particular, we have studied these systems by photoelectrochemical methods (cyclic voltammetry and chronoamperometry) [6,7], (localized) surface plasmon resonance spectroscopy [6,7], and UV-VIS spectroscopy. The trans-cis photoisomerization was identified in all adlayers and follows first-order kinetics with a life time of a few seconds under the experimental conditions. However, distinct differences between platform- and thiol-bound azobenzenes were found in respect of the thermally activated cis-trans backisomerization. Whereas for the latter species the cis isomer is very stable in the adlayers and in solution, the thermal cis-trans isomerization proceeds in the platform adlayers several orders of magnitude faster than in solution. The surprising instability of the cis isomer in the platform adlayers may be explained by a better electronic coupling between the azobenzene functions and the metal substrate.

[1] B. Baisch et al., J. Am. Chem. Soc., 131, 442 (2009)
[2] J. Kubitschke et al., Eur. J. Org. Chem. 5041-5055 (2010)
[3] S. Kuhn et al., PCCP, 12, 4481 (2010)
[4] U. Jung et al., Langmuir, 27, 5899 (2011)
[5] S. Kuhn et al., Chem. Commun., 47, 8880 (2011)
[6] U. Jung et al., Langmuir, 26, 13913 (2010)
[7] U. Jung et al., submitted to Adv. Mat.

In this work photoswitchable molecules are combined with polymer nanocomposites [1] containing metal nanoparticles or carbon nanotubes to achieve different functional properties. This includes a new concept of light-controlled impedance switching. Photoswitchable metal/polymer nanocomposite films and nanosheet capacitors were prepared by physical vapor deposition of Au and Pt nanoparticles onto spin-coated polymer/chromophore blends with a thickness around 200 nm, followed by embedding of nanoparticles into the polymer. These blends consist of poly(methylmethacrylate) films doped with azo dyes molecules. A second type of nanocomposite films were made from these blends mixed with carboxyl functionalized multiwall carbon nanotubes (MWCNT-COOH). High dye concentrations were achieved by functionalizing the azo molecules with tails and branches thus enhancing solubility. The composites show completely reversible light controlled impedance switching with capacitance changes > 50 % upon alternating irradiation with UV and blue light, respectively. [2]. Reversible light controlled conductance switching is shown for metal/polymer and MWCNT/nanocomposite films near the percolation threshold. For the metal nanoparticle containing composites this is attributed to changes in the metal nanoparticle separations 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 [3]. In contrast, the behavior of the MWCNT/nanocomposite films arrears to be dominated by electronic effects.

[1] F. Faupel, V. Zaporojtchenko, T. Strunskus, M. Elbahri, Adv. Eng. Mat. 12, 1177 (2010)
[2] V. Zaporojtchenko. C. Pakula, S. W. Basuki, T. Strunskus, D. Zargarani, R. Herges, F. Faupel, Appl. Phys. A. 102, 421 (2011).
[3] C. Pakula, V. Zaporojtchenko, T. Strunskus, D. Zargarani, R. Herges, F. Faupel, Nanotechnol. 21, 465201 (2010).

Antifreeze proteins (AFPs) prevent some organisms from freezing and help others to tolerate freezing. These highly diverse proteins are freely soluble in water and yet irreversibly bind to water in its solid state to inhibit ice crystal growth. The ice-binding site (IBS) of an antifreeze protein is typically flat, extensive, and relatively hydrophobic compared to other surfaces of the protein. There is increasing evidence for a binding mechanism where the IBS organizes surface waters around hydrophobic groups into a clathrate structure that is anchored to the protein by hydrogen bonding. These ice-like surface waters match those of the quasi-liquid layer next to ice and the two ordered layers merge and turn to ice. Thus the AFP helps form the ligand to which it binds. The activity of AFPs can be increased by joining them to other proteins, where the size of the fusion protein is proportional to the increase in activity. Even greater activity is attained by increasing the surface area of the IBS. Ice nucleating proteins (INPs) have the opposite effect to AFPs by promoting freezing at high sub-zero temperatures. Modeling has shown that INPs look like much larger versions of some AFPs. By extension, the mechanism of ice nucleation is thought to be similar to ice binding and involves the INPs ordering sufficient ice-like water molecules on their surface to form a homogeneous ice nucleus that initiates freezing.

Supported by CIHR

Our approach to engineer cellular environments is based on self-organizing spatial positioning of single signaling molecules attached to synthetic extracellular matrices, which offers the highest spatial resolution with respect to the position of single signaling molecules. This approach allows tuning tissue with respect to its most relevant properties, i.e., viscoelasticity, peptide composition, nanotopography and spatial nanopatterning of signaling molecule. Such materials are defined as “nano-digital materials” since they enable the counting of individual signaling molecules, separated by a biologically inert background. Within these materials, the regulation of cellular responses is based on a biologically inert background which does not initiate any cell activation, which is then patterned with specific signaling molecules such as peptide ligands in well defined nanoscopic geometries. This approach is very powerful, since it enables the testing of cellular responses to individual, specific signaling molecules and their spatial ordering. Detailed consideration is also given to the fact that protein clusters such as those found at focal adhesion sites represent, to a large extent, hierarchically-organized cooperativity among various proteins. We found that integrin cluster have a functional packing density which is defined by an integrin-integrin spacing of approximately 68 nanometers. Such critical spacing values vary as matter of transmembrane receptor choice of interest. We have also developed methods which allows the light initiated activation of adhesion processes by switching the chemical composition of the extracellular matrix. This enabled us to identify the frequency of leader cell formation in collective cell migration as a matter of initial cell cluster pattern size and geometry. Moreover, “nano-digital supports” such as those described herein are clearly capable of involvement in such dynamic cellular processes as protein ordering at the cell’s periphery which in turn leads to programming cell responses.

The most frequently used method to attach functional molecules to gold surfaces is using thiols as anchor groups and alkyl chains as spacers. Disadvantages are the lack of free volume for molecular isomerization/switching in densely packed monolayers, and the fact that in sub-monolayers these fluffy molecules tend to lie flat on the surface. We avoid these problems by using molecular platforms as anchor groups, and stiff ethynyl or phenyl units as spacers. Functional molecules (switches) are placed in well-organized monolayers upright like lanterns on pedestals. Based on the “platform approach” a number of functional surfaces have been prepared. Currently, azimuthal rotors (a)), and a molecular muscle (b)) are investigated. Platform design also includes the development of volatile molecules for vacuum deposition or suitable substituted platforms for ESI deposition and STM investigation.

Figure. Model calculations: a) Zn-porphyrin mounted on a platform via an ethynyl pivot joint, and b) azobenzene connecting two phenylethynyl posts each mounted on a platform (molecular muscle).

[1] B. Baisch, D. Raffa, U. Jung, O. Magnussen, C. Nicolas, J. Lacour, J. Kubitschke, R. Herges, J. Am. Chem. Soc. 2009, 131, 442-443.
[2] J. Kubitschke, C. Näther, R. Herges, Eur. J. Org. Chem. 2010, 5041-5055.
[3] 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.
[4] S. Kuhn, U. Jung, S. Ulrich, R. Herges and O. Magnussen, Chem. Commun. 2011 , 47, 8880-8882.
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Ultrathin insulating films on metal substrates facilitate the use of the scanning tunneling microscope (STM) to study the electronic transport properties of single molecules in the weak coupling limit. The ionic relaxations in a polar insulator lead to a charge bi-stability in some adsorbed atoms and molecules. It is shown that control over the charge-state of individual molecules in such systems can be obtained by choosing a substrate system with an appropriate work function. We study the spatial distribution of the additional charge by suitable subtraction of low-voltage STM images of the adsorbates in their different charge states. These difference images show marked intra-molecular contrast [1]. In addition, we investigated C20S2H12 molecules adsorbed on ultrathin layers of NaCl in our combined STM/AFM setup. These non-planar molecules exist in two stable conformations. By means of excitations from inelastic tunneling electrons we can switch between both conformations. We present atomic force microscopy (AFM) measurements with submolecular resolution directly revealing the conformational changes [2]. From AFM data and taking the chirality of the molecules into account, we could unambiguously determine the pathway of the conformational change. Hence, the AFM channel reveals additional information that is truly complementary to the STM data set.

References:
[1] I. Swart, T. Sonnleitner, and J. Repp, Nano Letters 11, 1580 (2011).
[2] N. Pavliček, B. Fleury, M. Neu, J. Niedenführ, C. Herranz-Lancho, M. Ruben, and J. Repp, Phys. Rev. Lett. 108, 086101 (2012).

Molecules with switchable magnetic and electronic properties are promising building blocks for spintronics. The magnetic and electronic property of organo-metallic molecules may be manipulated via controlling the ligand field on the metal ion. An electron induced spin switching in a spin cross-over molecule and controlled de-coordination/coordination of ligand from/to the metal center of Fe-pophyrin will be discussed.