Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 2: Metal substrates: Solid-liquid interfaces
O 2.5: Vortrag
Montag, 22. März 2010, 12:15–12:30, H31
About the Orientation of Viologen Monolayers on a Cu [1 0 0] Electrode Surface — •Melanie Röefzaad1, Vlad Zamlynny2, and Klaus Wandelt1 — 1Institute for Physical and Theoretical Chemistry, University of Bonn — 2Chemistry Department, Acadia University, Canada
Detailed investigations of the metal/electrolyte interface in presence of the redox active 4,4`-Bipyridin with different substituents at 1,1`-position have been done combining Infrared Reflection Absorption Spectroscopy (IRRAS) and Cyclic Voltammetry (CV). To reveal indications about the orientation of certain parts of the molecule in the adsorbed monolayer and their changes, the Polarization Modulated IRRAS was applied.[1,2] Calculations showed that in general all viologen species adsorb with the longer molecular axis parallel to the surface. In contrast the orientation of the ring planes of the bipyridine moiety changes after the reduction process. For Dibenzylviologen (DBV) the angles with respect to the surface normal have been calculated to ~20° for the dication and to ~70° for the radical-cation. In the same way orientations of alkyl substituents were investigated. For example Heptylviologen shows a straightening up of the long alkyl chains, from 50° to 24° with respect to the surface normal, while lowering the potential. This orientation change is mainly caused by decreasing the area per molecule (ApM) with a closer packing of the stacking rows.
[1] H. Seki, K. Kunimatsu, W. G. Golden, Appl. Spectroscopy 1985, 39, 437.
[2] A. N. Parikh, D. L. Allara, J. Chem. Phys. 1992, 96, 927.