Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 18: Poster Session I - MA 141/144 (Atomic Wires; Size-Selected Clusters; Nanostructures; Metal Substrates: Clean Surfaces+Adsorption of Organic / Bio Molecules+Solid-Liquid Interfaces+Adsorption of O and/or H; Surface or Interface Magnetism; Oxides and Insulators: Clean Surfaces)

O 18.34: Poster

Montag, 25. Februar 2008, 18:30–19:30, Poster F

FT IRRAS Studies of Potential-Controlled Transformations of a Monolayer of Dibenzylviologen adsorbed on a Cu(100) Electrode Surface — •Melanie Röefzaad, Duc Thanh Pham, Peter Broekmann, and Klaus Wandelt — Institut für Physikalische und Theoretische Chemie, Universität Bonn

Fourier transform infrared reflection absorption spectroscopy (FT IRRAS) has been combined with cyclic voltammetry (CV) to monitor the potential induced transformations of a monolayer formed by the redoxactive 1,1′-dibenzyl-4,4′-bipyridinium (dibenzyl-viologens or DBV) on a chloride pre-covered Cu(100) electrode surface. Both the dication (DBV²⁺) and the radical cation (DBV^+·) could be detected. The DBV²⁺ has been found to adsorb at positive electrode potentials with its main molecular axis parallel to the surface in a nearly face-on orientation. Lowering the potential beyond the thermodynamic reduction potential results in a phase transition with the DBV^+· molecule in a more side-on orientation. These results are well consistent with previous in situ STM studies [1] where a distinct phase transition from a “cavitand” phase to a polymeric stacking phase has been observed. Spectra of this polymeric phase showed also the same characteristic bands as were detected after dibenzyl-viologen adsorption at potentials where isolated dimers (DBV⁺)₂ on the surface have been observed. This indicates that the formation of both phases is based on the same π-π- and spin paring interactions so that dimers and polymers can be hardly distinguished by IR-spectroscopy only.

[1] Pham et al., New J. Chem., 30 (2006), 1439