Molecular Switches: Elementary Processes and …4 Salzau-Meeting: "Molecular Switches: Elementary...

Joint meeting of Sfb 677 and Sfb 658

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Molecular Switches:

Elementary Processes and Applications

27. Mai – 29. Mai 2009

Kulturzentrum Schloss Salzau

Book of Abstracts

2 Salzau-Meeting: "Molecular Switches: Elementary Processes and Applications”

Salzau-Meeting: "Molecular Switches: Elementary Processes and Applications” 3

Salzau-Meeting on: "Molecular Switches: Elementary Processes

and Applications"

27. 5. – 29. 5. 2009, Kulturzentrum Schloss Salzau

Scientific program

Tuesday, May 26 17:00 – 19:00 Arrival and registration

18:30 – 20:30 Dinner

Wednesday, May 27 7:00 – 8:30 Breakfast

9:00 – 9:30 Arrival and registration

9:30 – 9:40 Rainer Herges (CAU, Kiel)

Welcome and general information

Session: Solids and Materials I (Chair: O. Magnussen)

9:40 – 10:15 Michael Grunze (Univ. Heidelberg)

Chemical and physical cues for bioactive surfaces

10:15 – 10:25 Discussion

10:25 – 11:00 Christof Wöll (Univ. Bochum)

Interfacial Systems Chemistry: Fundamental Studies on Organic Surfaces Using Well-defined Model Systems


11:10 – 11:50 Coffee break

Session: Solids and Materials II (chair: E. Quandt)

11:50 – 12:15 Franz Faupel (CAU Kiel)

Sensors and switches based on polymer-metal nanocomposites near the percolation threshold


12:25 – 13:50 Wolfgang Bensch (CAU Kiel)

Functionalization of SBA-15 with a photoswitchable azobenzene 12:50 – 13:00 Discussion


13:00 – 14:30 Lunch

Session: Supramolecular Chemistry I (Chair: S. Hecht)

14:30 – 15:05 Frank Würthner (Univ. Würzburg)

Dye Assemblies for Supramolecular Electronics and Photovoltaics


15:15 – 15:50 Milko van der Boom (Weizmann Institute)

Sensing and Molecular Boolean Logic with Surface-Confined Metal Complexes



Session: Supramolecular Chemistry II (Chair: F. Tuczek)

16:45 – 17.10 Stefan Hecht (FU Berlin)

Designing Surface-Confined Switches


17:20 – 17:35 Ulrich Lüning (CAU Kiel)

Towards a light driven proton pump


17:55 – 18:30 Leonhard Grill (FU Berlin)

Spatial periodicity in molecular switching: Azobenzene derivatives studied by STM


18:40 – 20:00 Dinner

20:00 Poster Session


Thursday, May 28 7:00 – 8:30 Breakfast

Session: STM and Transport I (Chair: L. Grill)

9:00 – 9:35 Gerhard Meyer (ETH Zürich)

Scanning Probe Microscopy of Adsorbates on Insulating Films: From Manipulation of the Charge State to Imaging of Individual Molecular Orbitals and Bond Formation


9:45 – 10:20 Abraham Nitzan (Univ. Tel Aviv)

Optical Effects in Molecular Conduction



Session: STM and Transport II (Chair: J. Kröger)

11:15 – 11:40 Yongfeng Wang (CAU Kiel)

Molecule Switching Induced by Electrons


11:50 – 12:15 Jose I. Pascual (FU Berlin)

Molecular chemistry at surfaces: Ring opening reaction of Spiropyrane molecules on metal surfaces


12:25 – 14:00 Lunch

Session: Molecular Architectures (Chair: U. Lüning)

14:00 – 14:35 Paolo Samori (Univ. Strasbourg)

Functional supramolecular architectures at surfaces


14:45 – 15:00 Jens Kubitschke (CAU Kiel)

The platform concept: design and synthesis

15:00 - 15:10 Discussion


15:10 – 15:20 Ulrich Jung (CAU Kiel)

The platform concept: surface structure and switching



Session: Ultrafast Dynamics I (Chair: M. Wolf)

16:15 – 16:40 Martin Weinelt (MBI Berlin)

Excitonic coupling in self-assembled monolayers of azobenzene-functionalized alkanethiols

16: 40 – 16:50 Discussion

16:50 – 17:15 Michael Bauer (CAU Kiel)

"Two-photon photoemission and angle-resolved photoemission of switchable molecules on surfaces"

17:15– 17:25 Discussion

17:25 – 18:00 Peter Gilch (LMU München)

One molecule - a lot to see: The various aspects of the photochemistry of o-nitrobenzaldehyde


19:00 Conference Dinner

Friday, May 29 7:00 – 8:30 Breakfast

Session: Ultrafast Dynamics II (Chair: M. Weinelt)

9:00 – 9:25 Falk Renth (CAU Kiel)

Ultrafast Dynamics of Molecular Switches: Conformer-specific Photochemistry and Effects of Intramolecular Constraints


9:35 – 9:100 Bernd Hartke (CAU Kiel)

Ultrafast Dynamics of Molecular Switches: ab-initio quantum chemistry and dynamics




Session : Photochemistry and Theory (Chair: J.I. Pascual)

10:55 – 11:20 Eric Mc Nellis (FHI Berlin)

Molecular Switches at Surfaces: The Role of Dispersive van der Waals interactions


11:30 – 11:55 Felix Leyßner (FU Berlin)

Optically and thermally induced isomerization of a molecular switch in direct contact with a metal surface


12:05 – 12:30 Peter Saalfrank (Univ. Potsdam)

Current-induced versus temperature-induced switching of single cyclo-octadiene molecules chemisorbed on a Si(001) surface


12:40 – 14:10 Lunch

Session: Spin Crossover Compounds (Chair: R. Herges)

14:10 – 14:45 Yann Garcia (Louvain-la-Neuve, Belgien)

Spin Crossover Coordination Networks: from Isolated Molecules to Functional Assemblies


14:55 – 15:20 Felix Tuczek (CAU Kiel)

Spin State Switching in Coordination Compounds


15:30 – 15:55 Andreas Grohmann (TU Berlin) On the nautical qualities of iron(ii) spin crossover compounds 15:55 – 16:05 Discussion 16:05 – 16:10 Closing Remarks


Abstracts

Session: Solids and Materials

Wednesday, May 27

9:40 – 10:15 Michael Grunze (Univ. Heidelberg)

Chemical and physical cues for bioactive surfaces

- abstract not available -

10:25 – 11:00 Christof Wöll (Univ. Bochum)


11:50 – 12:15 Franz Faupel (CAU Kiel)


12:25 – 13:50 Wolfgang Bensch (CAU Kiel)

Functionalization of SBA-15 with a photoswitchable azobenzene



Christof Wöll, Bochum

Functional interfaces play an important role in material science. Whereas more basic applications like corrosion inhibition or lubrication have been crucial for technological advances in past centuries more recently the spectrum of desired interface properties has expanded significantly. In addition to applications e.g. in the field of organic solar cells, where a rather complex, yet static architecture of rather heterogeneous components is employed (Graetzel cell), presently the rendering of dynamics to interfaces is becoming a challenge. In particular it is very attractive to realize interfaces which can be switched between two or more states by electrical signals or by illumination with light.

Many of these approaches require a grafting of suitable molecules to solid substrates; e.g. in case of electrical switching clearly a contact to electrodes is needed.

In this talk we will describe a general strategy to prepare structurally well-defined model systems for organic thin layers supported on solid substrates based on organothiols [1,2]. A number of case studies will be presented, illustrating the general approach to obtain a desired organic surface by first choosing a target molecule, which performs the desired function, and then attaching a thiol anchor group (-SH) to it. The second step consists of simply immersing an Au-substrate in an ethanolic solution of the thiolated target molecule, thus yielding thiolate-based self-assembled monolayers, SAMs.

An important goal of the talk is to demonstrate that this apparently straightforward approach which has in the past decade been adopted by a huge number of groups is prone to problems which are frequently difficult to identify. Often it is tacitly assumed that the grafting of thiol-based anchors to an Au-substrate is a rather trivial process, leading to two-dimensional arrangements of the target molecules exhibiting more or less the same properties already known from bulk studies (either bulk or solution). A few selected case studies will demonstrate that frequently SAMs with unexpected properties are obtained. First, the preparation conditions occasionally require a systematic optimization (see [3] for the case of a larger, aromatic target mode molecule, anthracene). Quite often also other, non-trivial complications can occur. These phenomena include the presence of structures within SAMs different from those predicted assuming the bulk geometry of the target molecules, reactivities which are substantially lower than those in the liquid phase, or packing-induced changes of relative conformational energies. The latter aspect is particularly important for light-induced conformational changes in organic molecules and illustrates that a systemic approach is needed for building sophisticated functional interfaces.

[1] J.C. Love, L.A. Estroff, J.K. Kriebel, R.G. Nuzzo, G.M. Whitesides, Self-assembled monolayers as a form of nanotechnology, Chem. Reviews 105, 1103 (2005)

[2] M. Kind, Ch. Wöll, Dünnstschichten - Maßgeschneiderte Organische Oberflächen, Chemie in unserer Zeit 2, 128-141 (2008)

[3] D. Käfer, G. Witte, P. Cyganik, A. Terfort, Ch. Wöll, A comprehensive study of self-assembled monolayers of anthracenethiol on gold: solvent effects, structure, and stability, J.Am.Chem.Soc. 128, 1723, 2006



Franz Faupel, Kiel

Nanocomposites consisting of metallic nanoparticles in a dielectric polymer matrix exhibit very interesting functional properties with applications ranging from optical filters [1] and high frequency soft magnetic materials [2] to antibacterial coatings [3]. In the present talk, we focus on nanocomposites near the percolation threshold, where the electronic properties change from metallic to insulating, and the electrical conductivity changes by many orders of magnitude [4]. Below percolation, electronic conductivity is governed by thermally activated hopping between neighboring nanoparticles. Since the tunneling probability depends exponentially on the particle separation this regime is very interesting for sensing applications [5]. Moreover, switchable devices can be obtained if suitable switches such as photosensitive molecules are incorporated into the structure [6].

The sensing ability of polymer based metal nanoparticle containing composites is demonstrated by sensors for organic vapors, where the swelling due to vapor sorption increases the nanoparticle separation. Selectivity is achieved via a fingerprinting approach taking advantage of the different vapor solubilities in different polymers. Concerning the switching by chromophores, azobenzene derivate molecules were incorporated in PMMA and other polymers. In order to stabilize the molecules against crystallization and migration branched side groups were attached. Optical switching proved to be fully reversible. The resulting changes in local free volume were also studied by means of positron annihilation lifetime spectroscopy at the positron beam in Munich.

For switching of the electrical resistivity, gold nanoparticles were either incorporated in the chromophore containing polymers or the nanocomposites were applied as a coating. In the ongoing investigations, optical switching of the resistivity was demonstrated, but the effect turned out to be small and to involve a drift which is still under study. In contrast, large and fully reversible effects were seen for optical switching of the capacity. In a separate approach we also explore switching of the resistivity in nanocomposites by a magnetic field using the large hysteresis and large strains in ferromagnetic shape memory alloys [7].

[1] A. Biswas, O. C. Aktas, U. Schürmann, U. Saeed, V. Zaporojtchenko, T. Strunskus and F. Faupel, Appl. Phys. Lett., 84, 2655, (2004).

[2] H. Greve, C. Pochstein, H. Takele, V. Zaporojtchenko, F. Faupel, A. Gerber, M. Frommberger, and E. Quandt, Appl. Phys. Lett. 89, 242501 (2006).

[3] V. Zaporojtchenko, R. Podschun, U. Schürmann, A. Kulkarni and F. Faupel, Nanotechnology, 17, 4904, (2006).

[4.-6] F. Faupel, V. Zaporojtchenko, T. Strunskus H. Greve, U. Schürmann, H. Takele, C. Hanisch, V. S. K. Chakravadhanula, N. Ni, A. Gerber, E. Quandt, and R. Podschun, Polymers & Polymer Composites , 16, 471 (2008).

[7] Bechtold, C.; Gerber, A.; Wuttig, M.; Quandt, E.; Magnetoelastic hysteresis in 5 M NiMnGa single crystals, Scripta Materialia 58 (2008), 1022-1024


Functionalization of SBA-15 with a photoswitchable azobenzene

Wolfgang Bensch, Kiel

Due to the very regular and variable nano-sized pores, SBA-15 is a suitable host material for anchoring photoswitchable molecules (azobenzenes) on the surface of the pores. Light induced trans-cis isomerization of the azobenzene changes the free space in the pores. The final goal of the project is the development of a nanofilter allowing the separation of small molecules. The functionalization of SBA-15 was achieved applying a two-step post-synthesis (grafting) approach. In contrast to a one-step synthesis, the two-step approach offers a good control of the switch density in the pores. In the first step, the hydroxyl groups on the surface of the SBA-15 pores reacted in a condensation reaction with (3-aminopropyl)-triethoxysilane (APTES). In the second step, the amine groups of APTES were reacted with 4 phenylazobenzoylchloride yielding the final azobenzene switch. The results of chemical analysis, X-ray diffraction, nitrogen sorption and solid state NMR evidence covalent bonding between the azobenzene molecules and the silica surface. The more stable trans-form of azobenzene requires more space than the cis-form. By irradiation with UV-light (wave length = 365 nm), isomerization from the trans- to the cis-form is induced. Switching back from the cis- to the trans-form is achieved with light at 440 nm or by heating to 100 Â°C. The trans-form shows a strong absorption at 325 nm, whereas the cis-form exhibits only a weak absorption. Switching from trans to cis, the absorption located at 325 nm significantly decreases. The reversibility of this switching process can be simply monitored by the decrease and increase of this significant absorption. The stability of the switched state is much longer in the solid than in solution.


Session: Supramolecular Chemistry

Wednesday, May 27

14:30 – 15:05 Frank Würthner (Univ. Würzburg)


15:15 – 15:50 Milko van der Boom (Weizmann Institute)


16:45 – 17.10 Stefan Hecht (FU Berlin)


17:20 – 17:35 Ulrich Lüning (CAU Kiel)


17:55 – 18:30 Leonhard Grill (FU Berlin)




Frank Würthner, Würzburg

Research on dye molecules has been continuing to be at the forefront of new developments in Chemistry owing to their versatile functional properties associated with pi-conjugation. On a supramolecular level, appropriately controlled spatial arrangement of dyes enables pivotal functions in nature, the most intriguing examples being provided by the light-harvesting systems of purple and green bacteria which contain a large number of chlorophyll and carotene chromophores organized in cyclic arrays or tubular architectures by non-covalent interactions.

During the last few years, we have intensively investigated the organization of merocyanine, porphyrin, and perylene bisimide dyes by non-covalent forces into desirable nanoscale architectures as well as liquid-crystalline and crystalline solid state materials.

In this lecture, I will provide a brief overview on our achievements in the preparation of defined dye assemblies and their functional properties that originate from proper pi-pi-stacking. Our results reveal efficient energy and charge transport along artificial dye assemblies. Thus, smart electronic and photofunctional materials based on self-assembled synthetic dyes became available that have prospect to be embedded in technical devices or to be applied in biological environments.



Milko van der Boom, Weizmann Institute

Exposing functional compounds to light, heat, metal ions, and/or an electric potential may result in a (reversible) process that transforms the system into another state characterized by different physicochemical properties. Integration of compounds that are selectively responsive to such external triggers in various matrices (e.g., polymers and plastics, polyelectrolytes, and thin films) is of much current interest. These stimuli responsive materials (SRMs) are expected to become important components in organic/polymer-based devices. Possible applications range from targeted drug delivery, sensing materials, artificial muscles, molecular electronics to Boolean logic.

We used surface-bound Os and Ru polypyridyl complexes to demonstrate ppm-level sensing of water, hexavalent chromium, and Boolean logic. These systems are electrochromic and can exist in one of two oxidation states (M2+/3+). Reaction of an oxidizing or reducing agent with the covalently immobilized complexes on glass substrates can convert the metal centers from one oxidation state to the other. The absorption of light is coupled with the oxidation state of the sensors, logic gates and circuits and provides the output for these monolayer-based devices. The set-up is highly robust, accurate, and can be reset. In addition, the formation and electrochromic properties of self-propagating molecular-based assemblies will be discussed.



Stefan Hecht, Berlin

In order to build up miniaturized devices, one of the key challenges is to control molecular function at surfaces. Switches represent a prototype of such functional molecules. In particular, azobenzene undergoing trans-cis isomerization of the N=N double bond has been well investigated in solution as well as in the gas phase. However, molecular switches on active, i.e. metallic, substrates have thus far been poorly explored and for this purpose scanning tunneling microscopy (STM) at low temperature constitutes a powerful tool since it allows imaging of single molecules as well as manipulation of discrete atoms and molecules.

We have recently shown that isomerization of 3,3',5,5'-tetra-tert-butylazobenzene (TBA) on Au(111) can be induced either by the STM-tip via a tunneling mechanism at small distances or via an electric field mediated process at large distances. Thereby, the choice of the substrate turns out to be crucial as TBA cannot be isomerized neither on Cu(111) nor on Au(100). Several other azobenzene derivatives have been prepared to elucidate the role of intrinsic electronic properties as well as the coupling to the substrate.

Furthermore, multiple azobenzene switches have been connected either covalently or non-covalently. Using the latter approach, discrete supramolecular azobenzene assemblies have been prepared and could be successfully manipulated using the STM-tip as well as periodic switching could be accomplished in a self-assembled monolayer of another derivative depending on the commensurability with the substrate. Here, we will discuss our most recent results in these and related areas.



Ulrich Lüning, Kiel

Using a rotaxane as backbone, transport of protons from one end of the rotaxane to the other shall be enabled by irradiation with light. For such a pump, the rotaxane must be equipped (i) with a ring containing a protonable site, (ii) with one photoacidic stopper (iii) with a positive charge in vicinity to the acid and (iv) with two different stations along the axle. One station consists of an amide which will bind the basic site of the ring by a hydrogen bond. Next to this station, an acid will be formed upon irradiation which will then protonate the ring. The positive charge in its vicinity will repulse the protonated ring and it will diffuse to the second station from which the proton can be liberated to the other side of the rotaxane. In total, light will induce an active transport of protons along the rotaxane.



Leonhard Grill, Berlin

We have investigated the switching behaviour of single M-TBA (methoxy-tetra-tert-butylazobenzene) molecules, which are based on an azobenzene core. Upon deposition at room temperature, these molecules, which are very similar to the previously studied TBA molecules [1,2], but exhibit an additional methoxy group, diffuse on the Au(111) surface and form highly ordered islands. In contrast to the TBA molecules, various molecular structures are found. Switching experiments (by applying voltage pulses) reveal that, although all molecules are chemically identical and adsorbed planar on the surface, their isomerization ability depends strongly on the surface structure. While molecules in some structures can be switched efficiently, no isomerization process could be induced in other structures. This shows that the surrounding molecules, i.e. direct atomic-scale environ-ment, of each molecule determines its switching capability.

Furthermore, we could show that not only the lateral environment, but also the substrate underneath plays a fundamental role for the isomerization. After switching many molecules, the cis isomers can form a regular switching lattice. Thus, some molecules are efficiently isomerized (probability > 85%), while others are rarely switched (probability < 6%). Our results show that this unexpected behaviour is due to the commensurability between the surface structure and the molecular layer. Hence, the exact adsorption site of each molecule on the Au(111) surface precisely determines its ability to be switched [3].



Postersession

Wednesday, May 27, 20:00 h - Location: Entrance Hall “Herrenhaus”

1) Light Driven Synthesis A. Gehl, H. Sell and R. Herges, (CAU Kiel) 2) Ultrafast Dynamics of Molecular Switches: Conformer-specific Photochemistry

and Effects of Intramolecular Constraints R. Siewertsen, F. Temps, F.Renth, J. B.Schönborn, B. Hartke, F. Sönnichsen, B.

Stehn-Buchheim, R. Herges (CAU Kiel), F. Strübe, J. Mattay (Uni Bielefeld) 3) Studies of Azobenzene-Containing Triazatriangulenium Adlayers on Au(111) U. Jung, O. Filinova, S. Kuhn, B. Baisch, D. Raffa, J. Kubitschke, R. Herges,

O. Magnussen, (CAU Kiel)

4) Switching molecules on surfaces – a platform approach Jens Kubitschke, (CAU Kiel) 5) Excitation and structural transformation of single adsorbed molecules induced by localized optical fields M. Breusing, S.Kühn and T. Elsässer, (MBI Berlin) 6) STM tip induced conformational changes of an imine-based molecular switch

on a Au(111) surface Ch. Lotze, N. Henningsen, K. Franke, G,Schulze, Y. Luo, R. Haag, and J. I.Pascual,

(FU Berlin) 7) Synthesis of a mechanically driven spiropyran switch for single-molecule force

spectroscopy Christian Glockner, (CAU Kiel) 8) Adsorption and photoisomerization of azobenzene derivatives on the surfaces of

layered compounds studied by photoelectron spectroscopy Eric Benjamin Ludwig, (CAU Kiel) 9) Switchable electro-optical properties of 2D chromophore/polymer/metal

nanocomposites near the percolation threshold Christina Pakula, (CAU Kiel) 10) Switchable, porous inorganic-organic hybrid compounds A. Reher, N. Stock, (CAU Kiel) 11) Photoswitchable Proton Transfer Based on 2-(2,4-Dinitrobenzyl)pyridine and its

Derivatives Catrin Goeschen, (CAU Kiel) 12) Quantum chemical and dynamical calculations for molecular switches J. B. Schönborn, O. Carstensen, J. Sielk, W. Thimm and B. Hartke


Light Driven Synthesis

A. Gehl, H. Sell and R. Herges Otto-Diels-Institute of Organic Chemistry, Christian-Albrechts-University Kiel

A crucial point in the development of artificial functional molecular systems is their energy supply. In our project we are developing a supramolecular system that is capable of converting light energy into chemical energy. Such a system could serve as a fuel source for nano systems. It would indirectly make light energy available independently of the location of the light energy input. The fuel system consists of the chemical equilibrium between inorganic isopolyoxoanions. To put light energy into this chemical subsystem a photoswitchable receptor is used, whose photoisomers exhibit different formation constants of the complexes with the various anions of the fuel system. Once the receptor, the anions and their complexes are at equlilibrium, the system will be disequilibrated by photoisomerizing the receptor and an energy rich polyoxoanion would be released. The stored chemical energy would be delivered at catalytic centres that catalyze the reverse reaction. Due to its high energy storage capacity the monophosphate/pyrophosphate-system would be appropriate as a fuel system. The first goal for the development of this system is to find a receptor whose photo isomers exhibit different affinities to the phosphate species. As a model for the phosphate anions the isomorphous vanadium oxoanios are useful because their condensation takes place at room temperature without a catalyst and the concentration of the different vanadate species can be easily determined by 51V-NMR-spectroscopy. Dinuclear zinc amine complexes are known to be good oxoanion binding units [1,2]. Linked by a photoswichable azobenzene moiety the distance between the zinc centres can be varied by photoisomerization. As a consequence of the geometry change the non-binding receptor cis-1 is converted into the pyrovanadate receptor trans-1.

[1] D.H. Vance, A.W. Czarnik, J.Am.Chem.Soc. 1994, 116, 9397-9398.

[2] D.H. Lee, J.H.Im, S.U.Son, Y.K.Chung, J. I.Hong, J.Am.Chem.Soc. 2003, 125, 7752



R. Siewertsen, F. Temps, F.Renth, J. B.Schönborn, B. Hartke Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel

F. Sönnichsen, B. Stehn-Buchheim, R. Herges Otto-Diels-Institut für Organische Chemie, Christian-Albrechts-Universität zu Kiel,

F. Strübe, J. Mattay Lehrstuhl Organische Chemie 1, Fakultät für Chemie, Universität Bielefeld

The photo-induced reactions of molecular optical switches form the basis of numerous applications including optical data storage or light-driven molecular machines. A detailed knowledge of the underlying molecular ultrafast processes and their affecting factors is required for a rational design of optimized functional optical devices. We have studied prototypical photochromic furylfulgides and severely constrained azobenzene molecular switches by femtosecond time-resolved spectroscopy and by quantum-chemical calculations.

Fulgides and their derivates are thermally irreversible photochromic molecular switches that rely on the reversible E C ring closure, with the parallel E Z isomerisation as competing side reaction. Broadband transient absorption data after excitation of (E)-2-[1-(2,5-dimethyl-3-furyl)-ethylidene]-3-isopropylidene succinic anhydride (1E) gave time constants of 0.1 and 0.25 ps for the E C ring closure and E Z isomerisation, with a 2:1 product yield ratio. The results are consistent with conformer-specific photoreactions of 1E, where the s-cis conformer () forms the (C)-isomer and the s-trans conformer () reacts to the (Z)-isomer, or alternatively, with pathways originating from the photoexcited -conformer that involve an ultrafast branching of the excited-state wave-packet. The isomerisation times and TDDFT calculations suggest that the reactions proceed via distinctive conical intersections and that an optically dark intermediate state may be involved. A similar, sterically more demanding furylfulgide showed E C ring closure also with 0.1 ps, but only negligible E Z isomerisation. This indicates a strong steric effect on the photoreactions, which we are currently investigating further.

The bridged azobenzene (AB) derivative 5,6-dihydrodibenzo[c,g][1,2]diazocine (2) offers unique opportunities to study the Z E and E Z photoisomerizations of AB switches in the presence of restricted conformational freedom and ring strain. The severe intramolecular constraints cause the (Z)-isomer to be thermodynamically stable and a clear separation of the S1 absorption bands of both isomers with maxima at 405 nm (2Z) and 490 nm (2E), i.e., improved photochromic properties as compared to AB. Transient absorption measurements after S1 excitation yielded isomerisation times of 0.28 ps (2Z) and 0.35 ps (2E), suggesting barrierless excited-state reaction pathways via conical intersections. A torsional pathway on a complex isomerisation coordinate involving a conical intersection can be inferred from TDDFT and CASSCF calculations. The improved photochromic properties, high quantum yields and ultrafast time scales of the photoisomerisations make 2 a promising candidate as molecular optical switch especially at low temperatures.


Studies of Azobenzene-Containing Triazatriangulenium Adlayers on Au(111)

U. Jung1, O. Filinova1, S. Kuhn1, B. Baisch1, D. Raffa1, J. Kubitschke2, R. Herges2, O. Magnussen1

1Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Univ. zu Kiel 2Institut für Organische Chemie, Christian-Albrechts-Universität zu Kiel,

The preparation and characterization of molecular adsorbate layers on metallic substrates is an important area of interfacial physics. Self-assembled adsorbate layers of photo- or redoxswitchable compounds are appropriate for a multitude of applications and consequently have attracted huge interest [1, 2]. One of the most frequently studied class of photoswitchable compounds are the derivatives of azobenzene, which can undergo cis-trans isomerization in selective photo- [3] or electrochemical [4] induced processes. However, the isomerization of the azobenzene moieties in self-assembled monolayers can be strongly influenced or even totally quenched by steric effects [5]. Hence, for the preparation of highly-ordered adlayers exhibiting reversible photoswitching, it is necessary that the intermolecular spacings are large enough and well-defined. It is also essential to have a sufficient spacer unit between the switchable functionalities and the surface to avoid quenching effects. Furthermore, for selective photoswitching it is prerequisite to control the orientation of the switchable moieties relative to the surface. In this work, studies of self-assembled adlayers of different azobenzene-containing derivatives of the triazatriangulenium platform [6, 7] on single crystalline Au(111) substrates are presented. These adlayers were characterized by structure-sensitive (STM), spectroscopic (surface plasmon resonance spectroscopy and Raman spectroscopy), as well as electrochemical methods (cyclic voltammetry). It was found that these compounds form hexagonal adlayers with intermolecular distances in the range of 11 – 13 Å, which are controllable by the length of the alkyl side chain. Additionally, the photoswitchablity of these adlayers was studied by means of photoelectrochemical experiments and surface plasmon resonance spectroscopy. For all of these layers trans-cis isomerisation with half lives of a few 10 s were found. In addition, switching from cis to trans isomer by thermal relaxation was observed at a similar time scale.

[1] Ulman, Chem. Rev. (1996), 96, 1533 [2] Schreiber, Prog. Surf. Sci. (2000), 65, 151 [3] Hartley, J. Chem. Soc. (1938), 633 [4] Laviron et al., J. Electroanal. Chem. (1980), 111, 337 [5] Tamada et al., Langmuir (2002), 18, 5239 [6] Laursen et al., Angew. Chem. Int. Ed. (2000), 39, 3432 [7] Baisch et al., J. Am. Chem. Soc. (2009), 131, 442


Switching molecules on surfaces – a platform approach

Jens Kubitschke, Christian-Albrechts-Universität zu Kiel

Molecular switches such as azobenzenes and other photochromic molecules are well investigated in solution. In our project we are developing methods to attach azobenzene derivatives on metals, e.g. Au(111) to obtain functional surfaces. To achieve high switching quantum yields with UV (trans/cis-) and visible light (cis/trans-isomerization) and efficient functionality (e.g. data storage, surface property switching, directed motion) the azobenzene has to be mounted in a well defined orientation and distance with respect to the surface and to each other. To achieve that goal, we attach the azobenzene in an upright position to a molecular platform, the so called TATA (triazatriangulenium) platform.[1] The azobenzene is attached covalently to the central carbon atom and perpendicular to the plane of the platform (like a lantern on a supporting stand). The TATA platform itself as well as the functionalized platform form hexagonally ordered monolayers on Au(111) surfaces by self assembly.[2] By increasing the length of the side chains of the platform the intermolecular distance can be tuned.[2] The cis/trans switching quantum yields of the azobenzene units are by far superior to previously investigated alkane-thiol fixed azobenzenes.[3]

[1] B. W. Laursen, F. C. Krebs, Chem. Eur. J. 2001, 7, 1773-1783 [2] B. Baisch, D. Raffa, U. Jung, O. M. Magnussen, C. Nicolas, J. Lacour, J. Kubitschke,

R. Herges, J. Am. Chem. Soc. 2009, 131, 442-443. [3] S. D. Evans, S. R. Johnson, H. Ringsdorf, L. M. Williams, H. Wolf, Langmuir 1998,

14, 6436-6440.


Excitation and structural transformation of single adsorbed molecules induced by localized optical fields

M. Breusing, S.Kühn and T. Elsässer, Max-Born-Institut, Berlin

Fulgimide photoswitches perform a ring opening/closing isomerization under green/ ultraviolet illumination that lead to decoloration/coloroation. Our goal is to optically investigate and control the behaviour of these switches attached to surfaces down to the smallest number of molecules. For this purpose we apply the technique of scanning probe optical microscopy taking benefit of the optical field enhancement at a nanoscopic, metallic tip. This technique enables the study of optical material properties at the single molecule level. Well defined and reproducible samples are crucial for this systematic study. These are prepared by self-assebley of oriented fulgimide monolayers on silicon substrates in collaboration with C. Rück-Braun at the TU-Berlin.


STM tip induced conformational changes of an imine-based molecular switch on a Au(111) surface

Ch. Lotze1, N. Henningsen1, K. Franke1, G,Schulze1, Y. Luo2, R. Haag2, and J. I.Pascual1

1Inst. f. Experimentalphysik, Freie Universität Berlin 2Inst. f. organische Chemie, Freie Universität Berlin.

Azobenzene-based molecules exhibit a cis-trans configurational photoisomerisation in solution. Recently, the adsorption properties of azobenzene derivatives have been investigated on different metal surfaces in order to explore the possible changes in the film properties induced by external stimuli. In azobenzene, the diazo-bridge is a key group for the isomerization process. Its interaction with a metal surface is dominated through the N lone-pair electrons [1], which reduces the efficiency of the conformational change. In order to reduce the molecule-surface interaction, we explore an alternative molecular architecture by substituting the diazo-bridge (-N=N-) of azobenzene by an imine-group (-N=CH-). We have investigated the iminebased compound para-carboxyl-di-benzene-imine (PCI) adsorbed on a Au(111) surface. The carboxylic terminations mediates the formation of strongly bonded molecular dimers, which align in ordered rows preferentially following the fcc regions of the Au(111) herringbone reconstruction. Low temperature scanning tunneling microscopy was used to induce conformational changes between trans and cis state of individual molecules in a molecular monolayer.

[1] N. Henningsen, R. Rurali, K. J. Franke, I. Fernández-Torrente, and J. I. Pascual, Appl. Phys. A 93, 241 (2008)


Synthesis of a mechanically driven spiropyran switch for single-molecule force spectroscopy

Christian Glockner, Christian-Albrechts-Universität zu Kiel

The synthesis of a spiropyran with two PEG spacers is presented which should be acting as a molecular switch, driven by mechanical force. The molecule should be covalently anchored between a glass surface and an AFM tip. In single-molecule force spectroscopy, the AFM tip is pulled away from the surface leading to stretching of the spacers and the spiropyran, finally leading to the rupture of the weakest bond in the chain. This should be most likely the spiro-C–O bond, which leads to the characteristically colorered merocyanine form. Changing back to the closed spiropyran form is thermally favored and should be possible by turning off the mechanical stimulus or, alternatively, by photon absorption. In first experiments with the new MFP-3D AFM, carboxymethylated amylose, which has got the same reactive groups as the spiropyran, has been used as a model molecule. At pH 2.0, the rupture forces were significantly lower compared to pH 7.4. At the same time, the rupture forces in strongly acidic environment exhibited a stronger load dependence than the ones measured under slightly basic conditions. This behavior is more consistent with a bond hydrolysis than with a homolytic rupture of a covalent bond.


Adsorption and photoisomerization of azobenzene derivatives on the surfaces of layered compounds studied by photoelectron spectroscopy

Eric Benjamin Ludwig, Christian-Albrechts-Universität zu Kiel

Azobenzene and its derivatives Disperse Orange 3 and „Azo-Tata“ were deposited in situ under UHV conditions on the surfaces of the metallic and semiconducting layered crystals TiTe2 and HfS2, respectively. These layered materials show van der Waals coupling between the layers, which presumably leads to a weak molecule-substrate coupling at the sample surface. This qualifies them as excellent substrates for the analysis of the pristine electronic structure of adsorbed molecules and their possible photoswitching behavior. Thin films were prepared by creating a partial pressure of the molecules inside the UHV main chamber and by holding the samples at temperatures below 120K. Coverages from sub-monolayer to several monolayers were realized. Photoelectron spectroscopy experiments were performed using a He discharge lamp and a SPECS Phoibos 150 analyzer. The form of the substrate peaks of azobenzene-adsorbed TiTe2 indicates Stranski-Krastanov-like film growth. When Disperse Orange 3 adsorbs on TiTe2, the substrate peaks exhibit a behavior, which may be accounted for by Stranski-Krastanov or Frank-van der Merwe growth. In addition some molecular orbitals show a small angular dispersion and an extra peak was observed. Calculations relate this peak to an aligned arrangement of the molecules. To photoisomerize the molecules, the samples were illuminated with a LED Power Pen (wavelength 365 nm, 3.5 W/cm2). Photoelectron spectra of pure azobenzene adsorbed on HfS2 suggest that the adsorbed molecules could be partially switched from trans to cis orientation, whilst there were no significant changes in the spectra of azobenzene and Disperse Orange 3 adsorbed on TiTe2. The stronger molecule-substrate coupling on metallic TiTe2 might prevent the switching process, leaving semiconducting HfS2 as a suitable substrate for further experiments.


Switchable electro-optical properties of 2D chromophore/polymer/metal nanocomposites near the percolation threshold

Christina Pakula, Christian-Albrechts-Universität zu Kiel

The trans-cis-isomerization of Azobenzene derivatives offers the possibility to use them in a variety of functional materials. In this project the photoinduced conformational change of azobenzene derivatives is used in combination with 2D clusterfilms of gold or gold-palladium to built light switchable resistors and capacitors. Blends of PMMA and different azobenzene ethers have been prepared by dissolution of chromophore and polymer in a common solvent. Thin chromophore/polymer films were obtained by spin-coating. Metal clusters and contacts were deposited subsequently either by thermal evaporation or via sputtering. Different mixing ratios of PMMA and the two azobenzene ethers and their physical properties have been examined. Also the time dependence of the switching behavior upon exposure to light of different wavelengths ranging from UV to the visible region was examined. Furthermore the stability of the composites was analyzed and investigated. At last the results of the photoswitchable changes in resistance and capacitance of the nanocomposites will be presented.


Switchable, porous inorganic-organic hybrid compounds

A. Reher, N. Stock, Institute of Inorganic Chemistry, Christian-Albrechts-University

Porous compounds, e.g. zeolites or MOFs (Metal-Organic-Frameworks) have been investigated extensively for their use in catalysis, ion exchange materials, gas storage, gas release or as hosts for host-guest-compounds.[1] Besides their highly ordered structures, MOFs exhibit high surface areas due to their big, accessible pores.[2] In our project we incorporate switchable dye molecules, based on azobenzene or azopyridine, into the pores of these hybrid compounds. There are three possibilities to incorporate the dye molecules. They can be adsoped, covalently bound to the organic linker or coordinated to the metal sites. Upon irradiation with light of different wavelengths cis-trans-isomerisation takes place which should change the length, required space, dipole moment and the polarity of the dyes. This should lead to changes in the sorption properties, i. e. the capacity, selectivity and kinetics. Therefore, it would be possible to find applications for our compounds as switchable gas release or gas storage materials.[3] Here we present our latest results on the coordination of the three different dyes (4-phenylazoaniline, 3-phenylazopyridine, 4-phenylazopyridine) to the chromium atom in Cr-MIL-101. The samples were synthesized by wetness-impregnation or under reflux of a solution of the dye in toluene. Using powder diffraction and sorption measurements as well as Raman-spectroscopy and elemental analyses, we were able to confirm the coordination of the chromophores to the Cr-MIL-101 structure. Furthermore, the reversible switching between the cis- and trans-isomer was confirmed by UV-VIS measurements.

[1] U. Mueller, M. Schubert, F. Teich, H. Puetter, K. Schierle-Arndt, J. Pastré, J. Mater. Chem. 2006, 16, 626.

[2] A. Sonnauer, F. Hoffmann, M. Fröba, L. Kienle, V.Duppel, M.Thommes, C. Serre, G. Férey, N. Stock, Angew. Chem. 2009, 121.

[3] A. Reher, Diplomarbeit, Christian-Albrechts-Universität, 2008


Photoswitchable Proton Transfer Based on 2-(2,4-Dinitrobenzyl)pyridine and its Derivatives

Catrin Goeschen, Christian-Albrechts-Universität zu Kiel

The light driven proton transport is one of the most important processes in nature. In the photosynthetic apparatus or in bacteriorhodopsin light energy is used to pump protons across a cell membrane. -DNBP new photo¬switchable acids were designed andBased on -DNBP undergoes an intramolecular proton transfer uponsynthesized. irradiation. Among other physical properties the acidity increases as a result of the light induced proton transfer. A disadvantage of is, beside the low reversibility of the switching process, the relatively short lifetime of the blue tautomer. In order to optimize the properties of the new photoswitchable acids the stabilization of the NH-form was attempted by proper substitution of the parent system. Several new photoswitchable acids were successfully synthesized. To access the new photochromic systems a new reaction had to be developed. Triethylsilyl functionalized methylpyridine derivatives were treated with cesium in the presence of di- and tri-nitrofluoro benzene leading directly to the new photochromic systems.


Quantum chemical and dynamical calculations for molecular switches

J. B. Schönborn, O. Carstensen, J. Sielk, W. Thimm and B. Hartke, Christian-Albrechts-Universität zu Kiel

Using multireference ab-initio methods, an excited-state potential energy surface for cyclohexadiene/hexatriene has been calculated, treating the two most important degrees of freedom explicitly and all others via full relaxation. On this surface, quantum mechanical wavepacket dynamics result in frequencies and deexcitation times in agreement with experimental data. Based on these data, cyclohexadiene can be ruled out as a model for furylfulgide type switches. Therefore, we are rationally designing systems that will serve as improved furylfulgide models and possible new types of molecular switches. In close cooperation with our experimental partners in project A1, we are investigating into the photochemical properties of bridged azobenzene derivatives, combining both high-level ab-initio quantum chemical methods and system-specifically refitted semiempirical surface-hopping direct dynamics


Session: STM and Transport

Thursday, May 28

9:00 – 9:35 Gerhard Meyer (ETH Zürich)


9:45 – 10:20 Abraham Nitzan (Univ. Tel Aviv)


11:15 – 11:40 Yongfeng Wang (CAU Kiel)


11:50 – 12:15 Jose I. Pascual (FU Berlin)




Gerhard Meyer, Zürich

Ultrathin insulating films on metal substrates are unique systems to use the scanning tunneling / atomic force microscope to study the electronic properties of single atoms and molecules, which are electronically decoupled from the metallic substrate.

Individual gold atoms on an ultrathin insulating sodium chloride film supported by a copper surface exhibit two different charge states, which are stabilized by the large ionic polarizability of the film [1]. The charge state and associated physical and chemical properties such as diffusion can be controlled by adding or removing a single electron to or from the adatom with a scanning tunneling microscope tip. The simple physical mechanism behind the charge bistability in this case suggests that this is a common phenomenon for adsorbates on polar insulating films. For example in the particular case of Ag adatoms even three different charge states could be observed [2]. Employing a low temperature tuning fork AFM the different charge states can be observed directly in the force signal.

In the case of molecules on ultrathin NaCl films the electronic decoupling allows the direct imaging of the unperturbed molecular orbitals. This will be shown for individual pentacene molecules [3]. Scanning tunneling spectroscopy of these double-barrier tunneling-junctions reveals strong electron-phonon coupling to NaCl phonons.

Using atomic/molecular manipulation a covalent bond between an individual pentacene molecule and a gold atom can be formed. This bond formation is reversible and different structural isomers can be produced. Direct imaging of the orbital hybridization upon bond formation provides insight into the energetic shifts and occupation of the molecular resonances.

Molecular switches will be an essential part of possible future molecular devices. The bistability in the position of the two hydrogen atoms in the inner cavity of single free-base naphthalocyanine molecules constitutes a two-level system that can be manipulated and probed by low-temperature scanning tunnelling microscopy [4]. When adsorbed on an ultrathin insulating film, the molecules can be switched in a controlled fashion between the two states by excitation induced by the inelastic tunnelling current. The tautomerization reaction can be probed by resonant tunnelling through the molecular orbitals. Coupling of the switching process such that charge injection in one molecule induced tautomerization in an adjacent molecule will be shown.

References: 1. J. Repp, G. Meyer, F.E. Olsson, M. Persson, Controlling the Charge State of Individual Gold Adatoms, Science 305, 493 (2004)

2. F. E. Olsson, S. Paavilainen, M. Persson, J. Repp, G. Meyer, Multiple Charge States of Ag Atoms on Ultrathin NaCl Films, Phys. Rev. Lett. 98, 176803 (2007)

3. J. Repp, G. Meyer, S. M. Stojkovic, A. Gourdon, C. Joachim, Molecules on Insulating Films: Scanning-Tunneling Microscopy Imaging of Individual Molecular Orbitals, Phys. Rev. Lett. 94 026803 (2005)

4. P. Liljeroth, J. Repp, G. Meyer, Current-Induced Hydrogen Tautomerization and Conductance Switching of Naphthalocyanine Molecules, Science 317, 1203 (2007)



Abraham Nitzan, Tel Aviv

Some of the principal issues in molecular conduction junctions are associated with their characterization and control. Presently, the main tool for characterizing such systems is their current response to an external (source drain or gate) voltage. An external voltage is also the principal real time control instrument available at present. In principle, light can also be used for these tasks. Several successful experiments involving light in molecular junctions, including surface enhanced Raman scattering (SERS) from such systems, show the feasibility and potential power of this approach. This is further underscored by recent observations of "giant" (SERS) that were attributed to molecules positioned in narrow gaps between metal particles - another type of nanojunction. I will describe our recent work on the optical phenomena in non-equilibrium molecular conduction junctions, focusing on the following subjects:

(a) Bias effects on the linear response of molecular junctions to external radiation fields. [M. Galperin and A. Nitzan, J. Chem. Phys. 124, 234709 (2006)]

(b) Light induced current in unbiased junctions. [M. Galperin and A. Nitzan, Phys. Rev. Lett. 95, 206802 (2005), B. D. Fainberg, M. Jouravlev and A. Nitzan, Phys. Rev. B 76, 245329 (2007), B. Fainberg and A. Nitzan, Phys. Stat. Sol. 2009]

(c) Raman scattering in biased molecular junctions. [M. Galperin, M.A. Ratner and A. Nitzan, Nano Letters, 9, 758 (2009), J. Chem. Phys. 130, 144109 (2009)]

(d) Electron transmission induced by circularly polarized light. [S. S. Skourtis, D. N. Beratan, A. Nitzan, R. Naaman and D. Waldeck, Phys. Rev. Lett. 101, 238103 (2008)].


Molecule Switching Induced by Electrons

Thiruvancheril Gopakumar, Kiel

Using a cryogenic scanning tunneling microscope, reversible switches of intermolecular bonds, molecule conformations and orientations were induced. Azobenzene molecules located at the end of azobenzene chains were controllably translated back and forth by reversibly forming and breaking hydrogen bonds to the adjacent azobenzene molecule. A conformational modification of Tin-Phthalocyanine was performed via the reversible vertical up and down movement of the central tin ion. This switch enables writing of patterns in ordered and densely packed molecule arrays [1]. Passing ballistic electron currents through C60 molecules, which was achieved by moving the tip of the microscope into contact with an individual molecule, was used to reversibly interconvert molecule orientations [2]. A first step to control the molecular magnetic moment was performed by adsorbing Iron-Phthalocyanine on ferromagnetic cobalt islands. The islands exhibit a moiré pattern with strongly localized Co d states, which organize the arrangement of the molecules [3]. Single-molecule spectroscopy provided evidence that the iron-phthalocyanine molecules are magnetized.

[1] Y. F. Wang, J. Kröger, R. Berndt, W.A. Hofer, J. Am. Chem. Soc. 131, 3639 (2009).

[2] N. Néel, L. Limot, J. Kröger, R. Berndt, Phys. Rev. B 77, 125431 (2008).

[3] T.G. Gopakumar, N. Néel, J. Kröger, R. Berndt, submitted to Phys. Rev. Lett. (2009).



Jose I. Pascual, Berlin

The ring-opening reaction of spiropyran (SP) to form merocyanine (MC) is a photochromic processes, which can be reversibly induced in solution. The interest in this basic reaction stems from the different properties of each isomer, regarding to structure (SP is chiral), electrical dipole moment (MC has a large dipole) and electronic structure (MC is coloured). In solution SP is the thermally stable isomer. Here, we report that on a metal surface, MC turns out to be more stable. We investigate the thermally induced ring-opening transitions from the organic photo switch 6-nitro-spriropyran to its merocyanine isomer on a Au(111) surfaces by means of low temperature scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS) and force-field simulations. Under submonolayer coverage, each isomer presents a very distinct behaviour in terms of electron properties and structure of the self-assembled molecular domains. Once that the merocyanine domains are created, they remain stable, suggesting that interaction of the conjugated planar backbone with the metal surface helps to stabilize this isomer on the metal. The ring opening reaction can be also induced by local electric currents conducted through the molecule by the STM tip.

co-authors: Gunnar Schulze, and Katharina Franke


Session: Molecular Architectures

Thursday, May 28

14:00 – 14:35 Paolo Samori (Univ. Strasbourg)


14:45 – 15:00 Jens Kubitschke (CAU Kiel)

The platform concept: design and synthesis

15:10 – 15:20 Ulrich Jung (CAU Kiel)

The platform concept: surface structure and switching

- abstract not available -



Paolo Samori, Strasbourg

The processing, nanopatterning, manipulation and quantitative study of the physico-chemical properties of multifunctional materials across multiple length scales are crucial for technological applications in organic electronics. Solvent vapour annealing (SVA) post-treatments of (macro)molecular thin films physisorbed on surfaces can be successfully employed to form crystalline electroactive architectures such as millimetre long crystalline fibers of the semiconducting n-type perylene-bis-dicarboximide (PDI)[1a] and p-type hexabenzocoronene[1b]. The mechanism of this process complies with an Avrami-type nucleation governed growth. [1a] Fibers formed using such a strategy revealed a 10-fold increase in conductivity compared to the pristine PDI thin layer. [1a]

Supramolecular recognition between pre-programmed building blocks incorporating electrically and optically active units can be successfully used to generate multifunctional bi- and multi-component nanopatterns with controlled geometries. To this end, highly directional non-covalent interactions among suitable molecular modules have been suc-cessfully employed, including metal-ligand among molecular tectons embedding anthra-cene moieties [2] and H-bonds among guanosine derivatives exposing oligothiophene side-groups,[3] to generate 2D pattern with a precision on the sub-nm scale. Furthermore we demonstrated for the first time that by applying a supramolecular approach to the development of chemisorbed bi-component SAMs on Au(111), it is possible to form multicomponent crystalline domains, thereby achieving sub-nm control over the mole-cular patterning of a surface. This represents the first, yet fundamental, step towards the controlled spatial confinement of single molecules or functional groups on a surface. This supramolecular multicomponent array allows potential recognition of target functional groups and could therefore lead to the detection of single-molecule properties. [4]

External stimuli can be used to manipulate single molecules and aggregates embedded in a supramolecular ensemble. Prototypes of light-powered mechano-chemical switches can be developed: Significantly, the photochemical isomerization of a new terminally thiolated azobiphenyl rigid rod, forming a single component and tightly packed SAM on metallic surfaces, was found by STM to be highly cooperative and to be complete over a molecular 2D crystal.[5a] Such an azobenzene SAM has been successfully used to modulate the current through metal-organic-metal junctions. By incorporating the azobenzene SAM between a Au(111) support and a metal coated AFM tip, we could detect a 30-fold difference in the current through the junction, providing the first example of conducting AFM measurement on a bi-stable system. [5b] When incorporated into a macroscopic Hg drop based junction the SAM could also operate as a current photoswitch; interestingly the light induced vertical displacement of the Hg drop revealed that our SAMs acts as light-powered cargo lifter generating a force per unit area as high as 1x105 N/m2..[5b] This result unambiguously demonstrates that our azobenzene SAM represents a prototype of a molecular machine able to transport mass, and in particular to act as a cargo lifter. [5c] Noteworthy, our SAMs undergoing cis-trans isomerization represents the first molecular switch/motor operating on a surface according to a cooperative process. Our responsive system can be used to gate optical signals, and therefore has potential for implementing logic operations on arrays of switching elements, and ultimately for high density data storage based on artificial molecular systems.


Change in pH can also be employed to trigger conformational transition in 2,6-bis(1-aryl-1,2,3-triazol-4-yl)pyridine (BTP) molecules physisorbed on surfaces, as observed with a sub-nm resolution by STM at the solid-liquid interface. Upon addition of trifluoroacetic acid two different BTP molecules, each forming a highly ordered physisorbed monolayer, underwent significant conformational changes from their "rosette" to their "tetragon" forms, as reflected in dramatically altered 2D self-assembly over large areas extending over hundreds of nanometers. [6]

Beyond imaging, [7] Scanning Probe Microscopies make it possible to study quantita-tively various physico-chemical properties of architectures based on organic molecules. We have focused our attention to exploration of the electronic properties of mono- [8] and multi-component functional nanostructures by Kelvin Probe Force Microscopy (KPFM).[9]. By KPFM the photovoltaic activity in electron acceptor/donor blends was quantitatively studied both on the hundreds of nanometers [10] and, for the first time, on the few nanometers scale. [11] These results are of paramount for both achieving a full understanding over the fundamental processes of exciton split and electron/hole diffusion in blends for photovoltaics, but also for the optimization of organic solar cells.

[1] (a) Adv. Funct. Mater. 2007, 17, 3791. (b) Small 2009, 5, 112.

[2] (a) Angew. Chem. Int. Ed.., 2007, 46, 245. (b) Adv. Mater. 2009, 21, 1131

[3] (a) Org. Lett. 2006, 8, 3125. (b) Chem. Eur. J., 2007, 13, 3757.

(c) Adv. Mater. 2008, 20, 2433

[4] Angew. Chem. Int. Ed. 2008, 47, 2484

[5] (a) PNAS 2007, 104, 9937. (b) J. Am. Chem. Soc. 2008, 130, 9192.

(c) Angew.Chem.Int.Ed. 2008, 47, 3407

[6] Chem. Eur. J. 2009, 15, 4788

[7] (a) J. Mater. Chem. 2004, 14, 1353. (b) Chem. Soc. Rev. 2005, 34, 551.

(c) Scanning probe microscopies beyond imaging (Guest Editor: P. Samori)

Wiley-VCH (2006).

[8] Adv. Funct. Mater. 2006, 16, 1407-1416. (b) J. Phys. Chem. C 2008, 112, 17368.

(c) Adv. Funct. Mater. 2008, 18, 907

[9] (a) Adv. Mater 2006, 18, 145-164. (b) Chem. Commun. , 2007, 3326-3337.

[10] (a) Adv. Funct Mater. 2007, 17, 472.

[11] (a) J. Am. Chem. Soc. 2008, 130, 780-781. (b) J. Am. Chem. Soc. 2008,

130, 14605.


Switching molecules on surfaces - a platform approach

Jens Kubitschke, Ulrich Jung, Kiel

Molecular switches such as azobenzenes and other photochromic molecules are well investigated in solution. In our project we are developing methods to attach azobenzene derivatives on metals, e.g. Au(111) to obtain functional surfaces. To achieve high switching quantum yields with UV (trans/cis-) and visible light (cis/trans-isomerization) and efficient functionality (e.g. data storage, surface property switching, directed motion) the azobenzene has to be mounted in a well defined orientation and distance with respect to the surface and to each other.

To achieve that goal, we attach the azobenzene in an upright position to a molecular platform, the so called TATA (triazatriangulenium) platform.[1] The azobenzene is attached covalently to the central carbon atom and perpendicular to the plane of the platform (like a lantern on a supporting stand). The TATA platform itself as well as the functionalized platform form hexagonally ordered monolayers on Au(111) surfaces by self assembly.[2] By increasing the length of the side chains of the platform the intermolecular distance can be tuned.[2] The cis/trans switching quantum yields of the azobenzene units are by far superior to previously investigated alkane-thiol fixed azobenzenes.[3]

[1] B. W. Laursen, F. C. Krebs, Chem. Eur. J. 2001, 7, 1773-1783.

[2] B. Baisch, D. Raffa, U. Jung, O. M. Magnussen, C. Nicolas, J. Lacour, J. Kubitschke, R. Herges, J. Am. Chem. Soc. 2009, 131, 442-443.

[3] S. D. Evans, S. R. Johnson, H. Ringsdorf, L. M. Williams, H. Wolf, Langmuir 1998, 14, 6436-6440.


Session: Ultrafast Dynamics

Thursday, May 28

16:15 – 16:40 Martin Weinelt (MBI Berlin)


16:50 – 17:15 Michael Bauer (CAU Kiel)

"Two-photon photoemission and angle-resolved photoemission of switchable molecules on surfaces"

17:25 – 18:00 Peter Gilch (LMU München)


Friday, May 29

9:00 – 9:25 Falk Renth (CAU Kiel)

Ultrafast Demagnetization: A Pedestrians View

9:35 – 9:100 Berndt Hartke (CAU Kiel) Ultrafast Dynamics of Molecular Switches: ab-initio quantum chemistry

and dynamics



Martin Weinelt, Berlin

The geometric structure and optical properties of self-assembled monolayers of azobenzene-functionalized alkanethiols have been investigated with respect to UV/Visible and near-edge X-ray absorption fine structure spectroscopy in combination with density-functional theory. By attaching a trifluoro-methyl endgroup to the chromophore both the molecular tilt and twist angle of the azobenzene moiety were determined. Based on a detailed structural analysis the energetic shifts observed in optical reflection spectroscopy and the formation of J and H aggregates can be qualitatively described within an extended dipole model. This substantiates sizeable excitonic coupling among the azobenzene chromophores as an important mechanism that strongly suppresses trans to cis isomerization in densely-packed self-assembled monolayers.


Two-photon photoemission and angle-resolved photoemission of switchable molecules on surfaces

Michael Bauer, Kiel

This talk gives an overview of the solid-state photoemission activities in the Kiel SFB 677. It is divided into two parts, which focus, on the one hand, on the ultrafast dynamics of a molecular switching process and, on the other hand, on the effect of layered substrate materials on the switching efficiency. The first part concentrates on tin-phthalocyanine (SnPc). This non-planar (shuttlecock-shaped) molecule can adsorb on metallic surfaces in two different orientations due to its specific geometry. Wang et al. have demonstrated switching between these geometries using the tip of a scanning tunneling microscope [1]. The question arises if also light-induced switching of the adsorbed molecule is possible. In a Two-Photon Photoemission study we monitored changes in the spectral signature of SnPc molecules adsorbed on Ag(111) in response to the illumination with femtosecond light pulses. Reversible changes are observed, which depend on the intensity of the illumination light. Time-resolved 2PPE measurements show, that the characteristic dynamics of the light-induced processes take place on a femto- to picosecond time scale. This ultrafast behavior indicates that mainly the electronic excitation and relaxation of the molecules are probed in the 2PPE study. In the second part, the adsorption and possible photoswitching of azobenzene and some derivatives on the surfaces of layered transition-metal dichalcogenides were investigated with angle-resolved photoemission spectroscopy (ARPES). The key motivation is that layered materials may turn out as ideal substrates because their inert surfaces should lead to weak molecule-substrate coupling and thus more efficient switching. Thin molecular films were prepared on metallic as well as semiconducting compounds under ultrahigh vacuum conditions. The characterization by ARPES provides some insight into the growth modes and molecular ordering. Most notably, however, significant and reproducible photoinduced changes in the photoemission spectra are found for certain molecule/substrate combinations. These are tentatively attributed to photoswitching of the molecules.

[1] Y. Wang, J. Kröger, R. Berndt, W.A. Hofer, J. Am. Chem. Soc. 131, 3639 (2009).



Peter Gilch, München

Many ortho-substituted nitroarenes are prone to photo-induced intramolecular redox reactions. The redox process can result in the release of a leaving group turning such nitroarenes into important photo-labile protecting groups. The photo-redox reaction of o-nitrobenzaldehyde yielding o- nitrosobenzoic acid is prototypical for this class of photo-reactions. We have performed a series of femtosecond experiments aiming at the mechanism of this reaction. These experiments will be discussed with regard to the following aspects: (i) How can the structure of short-lived intermediates be elucidated? (ii) How does the photon energy of the excitation light affect the reaction? (iii) What is the multiplicity of the reactive state? (iv) What is the impact of the vibrational excitation on reaction kinetics?



Falk Renth, Kiel

The photo-induced reactions of molecular optical switches are the basis for numerous applications such as optical memory and light-driven molecular machines. For an optimized rational design of functional optical devices, a detailed knowledge of the underlying molecular ultrafast processes and their affecting factors is required. We have studied prototypical photochromic furylfulgides and severely constrained azobenzene molecular switches by femtosecond time-resolved spectroscopy and by quantum-chemical calculations.

Our broadband transient absorption data of the parallel E - C ring closure and E - Z isomerisation after excitation of the thermally irreversible photochromic furylfulgide (E)-2-[1-(2,5-dimethyl-3-furyl)-ethylidene]-3-isopropylidene succinic anhydride (1E) are consistent with conformer-specific photoreactions of 1E, where the s-cis conformer forms the (C)-isomer and the s-trans conformer reacts to the (Z)-isomer. The distinct isomerisation times of 0.1 and 0.25 ps for the E - C ring closure and E - Z isomerisation and TDDFT calculations suggest that the reactions proceed via distinctive conical intersections. The slower time scale for the E - Z isomerisation might indicate a pathway that is not barrierless or involves an optically dark intermediate state. An alternative explanation would imply photo-excitation to a common origin in the Franck-Condon region of the -conformer and a subsequent ultrafast branching of the excited-state wave-packet. A similar, but sterically more demanding furylfulgide showed E - C ring closure also with 0.1 ps, but only negligible E - Z isomerisation. This indicates a strong steric effect on the photoreactions, which we are currently investigating further. We have also turned to the study of the related benzofurylfulgides, where the benzo-annulation provides steric hindrance for the furyl moiety.

The bridged azobenzene (AB) derivative 5,6-dihydrodibenzo[c,g][1,2]diazocine (2) offers unique opportunities to study the Z - E and E - Z photoisomerizations of AB switches in the presence of restricted conformational freedom and ring strain. The severe intramolecular constraints lead to a clear separation of the S1 absorption bands with maxima at 405 nm (2Z) and 490 nm (2E), i.e., improved photochromic properties, and a reversed thermodynamic stability of both isomers compared to the unbridged AB. Our transient absorption measurements gave isomerisation times of 0.28 ps (2Z) and 0.35 ps (2E) and suggest barrierless excited-state isomerisation reaction pathways via conical intersections. From TDDFT and CASSCF calculations, a photoisomerisation mechanism on an isomerisation coordinate involving torsion of the CNNC dihedral angle and a conical intersection could be inferred. The improved photochromic properties, high quantum yields and ultrafast photoisomerisations make 2 a promising candidate as molecular optical switch especially at low temperatures.


Ultrafast Dynamics of Molecular Switches: ab-initio quantum chemistry and dynamics

Bernd Hartke, Kiel

Thorough understanding photo-induced reactions of molecular optical switches in isolation and in complex environments can only arise from a tight interplay of experiment and theory. Therefore, in project A1, we are conducting both femtosecond time-resolved spectroscopy and theoretical simulations (both static electronic structure theory and dynamics calculations) in close cooperation, for the same set of prototype molecular switches.

As backbone model for furylfulgide switches, we have examined the photochemical ring opening of cyclohexadiene (CHD). With a systematic series of CASSCF/CASPT2 calculations, we have established a global excited-state potential energy surface in the two degrees of freedom that drive the reaction, including all other degrees of freedom via full relaxation. Reactive dynamics on this surface have been simulated using quantum-mechanical wavepacket propagations, resulting in good agreement with experimental data on the ultrafast photochemical dynamics of CHD. However, our theoretical data also indicate that CHD has certain defects as a model for furylfulgide. Therefore, we are currently examining several more elaborate molecular systems in order to establish a better furylfulgide model.

As a cheaper alternative to this expensive ab-initio approach, we are employing full-dimensional classical-mechanical surface-hopping trajectory simulations with on-the-fly calculation of forces, which are generated from a semiempirical configuration-interaction method. System-specific re-adjustments of the semiempirical parameters to CASSCF/ CASPT2 calculations for the molecule under study are performed with our global optimization algorithms, leading to ab-initio-quality results at a fraction of the cost. As a demonstration of this approach, we present the first photodynamics simulations for the bridged azobenzene derivative that is also in the focus of the experimental work within A1.

These initial investigations set the stage for future work, in particular for a systematic development of better model systems and new photoswitchable molecules, and for simulations of molecular switching against/by external forces and in confined spaces. Via QM/MM embedding, the latter avenue will be extended towards simulating the dynamics of molecular switches in polymer matrices, again in close cooperation with experimental work on such systems.


Session: Photochemistry and Theory

Friday, May 29

10:55 – 11:20 Eric Mc Nellis (FHI Berlin)


11:30 – 11:55 Felix Leyßner (FU Berlin)


12:05 – 12:30 Peter Saalfrank (Univ. Potsdam)




Eric McNellis, Berlin

Molecules with properties that due to external stimuli may be reversibly changed between defined states, or so called 'molecular switches', are envisioned as a key component of a future molecular nanotechnology. In this context, switches affixed at solid surfaces are of particular interest. We have in previous work studied the Azobenzene (C12H10N2) switch adsorbed at coinage metal surfaces, using Density Functional Theory (DFT) in the Generalized Gradient Approximation (GGA). At DFT-GGA level of theory, the switch - surface interaction ranges from weak chemisorption to pure physisorption, which combined with the adsorbate size, implies that known inadequacies of DFT in the description of the dispersive molecular van der Waals interactions significantly influence the results. The state of the art remedy for these shortcomings are semi-empirical pair potentials added as a correction to the DFT total energy. We have extended our previous study to include several such schemes in the description of Azobenzene adsorption at coinage metals. The esulting changes to both geometric structure and adsorption energies are substantial, in some cases significantly altering the pure DFT picture. Differences between schemes are also large. We discuss these results and varying performance of published schemes in the greater context of molecular adsorption at metal surfaces.



Felix Leyßner, Berlin

Molecular switches represent a fascinating class of functional molecules, whose properties can be reversibly changed between different molecular states by excitation with light or other external stimuli. Using surface science concepts like self assembly to align such molecules in a well defined geometry at solid surfaces, new functional properties may arise, which are relevant for different fields like, e.g., molecular electronics, sensing or biocompatible interÂfaces. For a microscopic understanding of molecular switching at surfaces, it is essential to obtain detailed knowledge on the underlying elementary processes, for instance the excitation mechanism in photoinduced switching.

We will present a case study of a specifically designed azobenzene derivative on a metal surface, namely tetra-tert-butyl-azobenzene (TBA) adsorbed on Au(111), which is so far one of the best studied system for which reversible conformational changes have been demonÂstrated. Using two-photon photoemission (2PPE) [1-3] enabled us to follow the photoinduced and thermally activated reversible switching of TBA in direct contact with a Au(111) surface. The trans/cis-isomerization of TBA is accompanied by reversible changes in the electronic structure of the molecules, allowing to gain mechanistic and quantitative insight into the switching process. Our results demonstrate the feasibility of molecular switching at metal surfaces, but also indicate that the switching properties of the surface-bound species are strongly modified by the interaction with a metal substrate.

[1] S. Hagen et al., Appl. Phys. A, 93 (2008) 253.

[2] S. Hagen et al., J. Chem. Phys., 129 (2008) 164102.

[3] M. Wolf and P. Tegeder, Surf. Sci. in press, 2009.



Peter Saalfrank, Potsdam

The biconformational switching of single cyclooctadiene molecules chemisorbed on a Si(001) surface was explored by quantum chemical and quantum dynamicalcalculations and low-temperature scanning tunneling microscopy experiments. The calculations rationalize the experimentally observedswitching driven by inelastic electron tunneling (IET) at~5 K. At higher temperatures, they predict a controllable crossover behavior between IET-driven and thermally activated switching, which is fully confirmed by experiment.


Session: Spin Crossover Compounds

Friday, May 29

14:10 – 14:45 Yann Garcia (Louvain-la-Neuve, Belgien)


14:55 – 15:20 Felix Tuczek (CAU Kiel)


15:30 – 15:55 Andreas Grohmann (TU Berlin)

On the nautical qualities of iron(ii) spin crossover compounds



Yann Garcia, Louvain-la-Neuve

The fast developments in advanced electronic technology call for new compounds showing a bistability behaviour on the nanometer scale. Spin crossover (SCO) molecular materials belong to an appealing class of switchable coordination compounds with spin state that can be reversibly triggered by temperature, pressure or electromagnetic radiation [1]. Most of the investigations have been carried out for coordination compounds incorporating 3d5, 3d6 and 3d7 transition metal ions in octahedral surrounding,[2] but the first crystal structures of a 3d4 system solved in both high-spin (HS) and low-spin (LS) states was recently communicated [3]. This phenomenon implies a variation of the ML6 geometry as well as of the unit cell, which can be tracked by X-ray diffraction. Although the origin of the SCO phenomenon is molecular, its cooperative manifestation depends on an efficient coupling between the SCO species in the crystal lattice through covalent and supramolecular interactions [4].

In this context, iron(II) 1,2,4-triazole and 1-R-tetrazole coordination polymers have attracted particular interest as their abrupt spin transition is generally associated with both hysteretic and thermochromic effects, thus providing a basis for their potential use in thermal display, memory devices and sensors [4]. We will demonstrate that the nature and mechanical character of the bridging ligand play a crucial role on the elastic transmission of molecular distortions associated to the thermally induced SCO of Fe(II) ions in 1D systems. We will also highlight the importance of the anionic sublattice dynamics on the spin transition of these compounds [5]. The importance of supramolecular interactions on the existence of the switching mechanism itself will be addressed too for 2D coordination polymers [6]. Recent developments on the use of a new range of thermochromic and photochromic switches will also be highlighted [7].

We acknowledge financial support from the IAP-VI INANOMAT (P6/17) and the FNRS (FRFC).

[1] P. Gütlich, Y. Garcia, H. Spiering, Magnetism: From Molecules to Materials IV, Wiley-VCH 2003, 8, 271.

[2] Y. Garcia, P. Gütlich, Top. Curr. Chem. 2004, 234, 49.

[3] (a) P. Guionneau, M. Marchivie, Y. Garcia, J. A. K. Howard, D. Chasseau, Phys. Rev. B 2005, 72, 214408. (b) Y. Garcia, H. Paulsen, V. Schünemann, A. X. Trautwein, J. A. Wolny, Phys. Chem. Chem. Phys. 2007, 9, 1194.

[4] Y. Garcia, V. Niel, M. C. Munoz, J. A. Real, Top. Curr. Chem. 2004, 233, 229.

[5] (a) Y. Garcia, S. J. Campbell, J. S. Lord, Y. Boland, V. Ksenofontov, P. Gütlich, J. Phys. Chem. B 2007, 111, 11111. (b) Y. Garcia, V. Ksenofontov, S. Mentior, M. M. Dirtu, C. Gieck, A. Bhatthacharjee, P. Gütlich, Chem. Eur. J. 2008, 14, 3745.

[6] Y. Garcia, G. Bravic, D. Chasseau, C. Gieck, W. Tremel, P. Gütlich, Inorg. Chem. 2005, 44, 9723.

[7] F. Robert, A. D. Naik, B. Tinant, R. Robiette, Y. Garcia, Chem. Eur. J. 2009, 15, 4327.



Felix Tuczek, Kiel

Transition-metal complexes with photoswitchable spin-states are an important class of molecular switches. One possibility to achieve photoinduced spin-state switching is the use of photoswitchable ligands that change the coordination number and/or the ligand field strength of the transition-metal complex upon irraditation with light. The talk addresses three topics which are centered around this theme:

(1) Ni-porphyrins with pyridine and azopyridine ligands: The electronic ground state of Nickel(II) porphyrins is S=0 without axial ligands and S=1 with one or two axial ligands. This can be exploited for the synthesis of Ni(II) complexes the spin state of which is switched by coordination and decoordination of axial ligands. With this goal in mind various azopyridine ligands have been synthesized. Coordination and light-induced decoordination of these ligands have been studied in detail. Preliminary investigations have been devoted to the determination of association constants for pyridine and amine ligands to Ni(II) porphyrins.

(2) Iron Complexes with azopyridine ligands. A â€œclassicâ € theme of transition-metal complexes with photoswitchable electronic ground states are Fe(II) and Fe(III) spin-crossover complexes. In the present project a Fe(III) spin-crossover complex with an axial azopyridine ligand is investigated. The ligand field of the complex can be switched between high-spin and low-spin a by a photoinduced cis-trans isomerization of the ligand.

(3) Surface fixation of complexes with photoswitchable ligands: In order to become addressable at a molecular scale transition-metal complexes with switchable ligands have to be attached to surfaces. Synthetic methods to achieve this goal are presented. The surface-fixed complexes are investigated with IRRAS (infrared reflection absorption spectroscopy), XPS, NEXAFS, AFM and STM.


On the nautical qualities of iron(ii) spin crossover compounds

Andreas Grohmann, Berlin

The talk will present two kinds of iron(ii) complex, data relating to their spin crossover behaviour in the solid state, and strategies to anchor ordered arrays on surfaces (gold, graphite). An ensemble showing unique spin characteristics will be discussed.


Appendix


Information about staying at Schloss Salzau

Dear Guest, Code Number (Restaurant): 0000

The castle will be open until 7 pm, however, you can leave the castle through the door near the restaurant after 7 pm. To enter again, you have to use the code number, which is during the whole conference the number 0000. Next to the door you will find a keyboard to type the number. As the meals are prepared freshly, please be on time, especially for lunch and dinner. After the meals, you are kindly requested to place your dishes on the carriage serving this purpose. Thank you! Departure:

Please leave the room till 10:00 a.m. and put the key in the box in the restaurant (castle). Phone: Downstairs in the cloakroom there is a pay phone. The office of the administration is

available during daytime, the number is 04303/180.

Internet: A wireless internet (WLan) connection is available. You can register your computer at office of the administration. The costs are 4 € for 3 days.

Room Plan: (Ground Floor Herrenhaus, Schloss Salzau)


Overview map of Schloss Salzau


Brief History

Landeskulturzentrum Salzau 24256 Salzau

Tel: 04303/180 Fax: 04303-18-164

Web: www.kulturzentrum-salzau.de

Salzau belongs to the manor houses in Schleswig-Holstein already mentioned in the most

ancient municipal record of Kiel (1264 – 1289). After several owners the privy councillor

an chamberlain Wulf Bloome acquired the landed estate close to the “Selenter” lake in

1758. A landed estate of 4000 ha including the neighbouring villages an outlying estates.

The Counts of Bloome were in possession of the estate for another 200 years. After a

great fire in 1881 the manor house was reconstructed by J.E. Mose (Silesian architect) in

only one year.

In the course of hereditary succession the manor house was passed into the possession of

the Counts of Thun and Hohenstein in 1945. Due to a partition in 1973 it was sold to a

businessman from Hamburg. Later on the Government of Schleswig-Holstein bought the

mansion with its adjoining buildings an the park. In 1988 the portal building and barn

followed. Since then the Government of Schleswig-Holstein uses it for different cultural

events an meetings.

Salzau is located about 20 km from Kiel, taking about thirty minutes to get by car.

Between the Baltic Sea an the “Holsteinische Schweiz” the visitor may find one of the

most beautiful landscapes of Schleswig-Holstein with a wealth of scenic and cultural-

historical characteristics. With the mansion, the concert barn an the affiliated orchestra

academy Salzau represents a central place for events of the Schleswig-Holstein Musik

Festival and became a symbol for musicians in Northern Germany. Since 1990 the

cultural centre has the main objective of being a lively place for meetings of all different

kinds e.g. seminars, art exhibitions, international exchanges, readings an last but not least

concerts of the “Schleswig-Holstein Musik Festival”.


Google Earth Views of Salzau


Scientific profiles of the Sfb 658 and Sfb 677 Sfb 658: The increasing miniaturization and integration in electronic devices and sensors opens the perspective to use molecules as building blocks for functional molecular nano-structures. For applications like molecular electronics it will be essential to control the switching between different molecular states, which in nature is often realized by photo-induced conformational changes. Controlled switching of molecular function requires the synthesis and design of appropriate molecular nanosystems and a basic understanding of structural and electronic properties including the interaction with the environment. In addition, there is a demand for active control by external stimuli like electromagnetic fields, forces and currents. The interaction of molecules with surfaces opens new per-spectives: It allows to assemble molecules with defined orientations and to vary the lateral couplings in a systematic manner. The contact of molecules to solid state interfaces is also essential to connect the molecular system with the outside world, in particular for electric transport. The Sfb 658 investigates molecular switching processes driven by external excitations in well defined molecular systems at solid surfaces. We focus on reversible conformational changes of individual molecules and ensembles leading to measurable changes of functional (e.g. optical, electronic or magnetic) properties of the system. Our focus on elementary processes includes investigation of all individual steps, physical parameters and interactions, which induce and influence the process of molecular switching. Research in the Sfb is based on various complementary methods from synthesis of molecular systems, characterization of structural and electronic properties by quantitative surfaces sciences techniques and theoretical modeling. The long-term goals are to develop novel functionalities, like cooperative switching processes, and criteria for applications in molecular functional devices. Sfb 677: Virtually, all technical engineering functions that are realized in our macro-scopic world have been implemented on a molecular scale by nature. Molecular pumps transport substances through cell membranes, motors fueled by ATP drive molecular vehicles along polymer tracks. Repair enzymes constantly control our genetic informa-tion, automatically uncovering and mending defects. A switching process triggered by external signals is the common basis for all aforementioned molecular or macroscopic functions and applications. Switching is not only the basic principle of digital data processing; it also serves as a fundamental step in the operation of motors, actuators, sensors and machinery of any kind. The Collaborative Research Centre aims at the implementation of essential and elementary functions using artificial (abiotic) systems on a molecular basis. Similar to information processing, the inherent miniaturization of technical processes to a molecular scale will result in a considerable increase in efficiency and performance as well as the development of new applications. Numerous examples from nature demonstrate that this should be feasible on a high level of sophistication. In this project as well as in nature, the smallest switchable unit is a molecule, which is embedded in a well defined surrounding and whose properties can be changed reversibly by light, concentration or redox gradients. Additional stimuli are electric fields, magnetic fields and electrons. Basic tasks such as transport, storage and information processing are realized at the nanometer scale by the controlled interaction of the elementary switch with the surrounding. We will design and synthesize new molecular switches that are optimized to perform these functions. They will be fixed on surfaces and colloid particles, introduced in cavities and pores or incorporated in polymer materials or nanocomposites. Thereby more sophisticated functions will be realized that will open new prospects beyond traditional technologies.

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