Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 44: Poster Session II (Semiconductors; Oxides and Insulators: Adsorption, Clean Surfaces, Epitaxy and Growth; Surface Chemical Reactions and Heterogeneous Catalysis; Surface or Interface Magnetism; Solid-Liquid Interfaces; Organic, Polymeric, Biomolecular Films; Particles and Clusters; Methods: Atomic and Electronic Structure; Time-resolved Spectroscopies)

O 44.69: Poster

Mittwoch, 28. März 2007, 17:00–19:30, Poster C

STM results on Electrochemical Surface Electron Transfer Reactions — •Duc Thanh Pham, Knud Gentz, Carolin Zörlein, Peter Broekmann, and Klaus Wandelt — Institut für Physikalische und Theoretische Chemie, Universität Bonn

The structural characterization of 1,1’-dibenzyl-4,4’ bipyridinium molecules (dibenzyl-viologen, DBV), adsorbed on a chloride modified Cu(100) electrode is studied by means of Cyclic Voltammetry (CV) and in-situ Scanning Tunneling Microscopy (STM), showing the formation of laterally well-ordered 2D-array of different supramolecular ensembles. By reducing the pre-existing di-cationic DBV²⁺ species to the corresponding radical mono-cation DBV^*+, a quasi-reversible phase transition is initiated from a cavitand phase to a stripe pattern. These structural motifs are widely independent on the electronic and structural substrate properties. While each cavitand consists of 4 individual DBV²⁺ sub-units arranged in a circular manner making this supramolecular cavitands chiral, the DBV^*+ in the stripe pattern are adsorbed with their main molecular axis parallel to the surface in a side-on adsorption geometry. However, by exchanging the pure supporting electrolyte for the viologen-containing solution in the potential regime where this phase transition takes place, it reveals two further metastable phases, which can be irreversibly transformed into the stripe pattern or the cavitand phase. In addition, chloride desorption through the viologen film is discussed as reason for an order-disorder transition within the viologen film at even more negative potentials.