Electron Spectroscopic Studies of Bis-(2,2‘-bipyridine)-(4,4‘-dicarboxy-2,2‘-bipyridine)-ruthenium(II) and Bis-(2,2‘-bipyridine)-(4,4‘-dicarboxy-2,2‘-bipyridine)-osmium(II) Adsorbed on Nanostructured TiO2 and ZnO Surfaces

The adsorption of the dyes bis-(2,2‘-bipyridine)-(4,4‘-dicarboxy-2,2‘-bipyridine)-ruthenium(II) and bis-(2,2‘-bipyridine)-(4,4‘-dicarboxy-2,2‘-bipyridine)-osmium(II) on nanostructured TiO2 and ZnO was investigated by photoelectron spectroscopy (PES) using synchrotron radiation. Comparison of the results gives insight into the electronic structure of the molecules, as well as to their interaction with the substrates. The identity of the central metal ion of the dye complex was found not to influence the bonding mode of the molecule on the surfaces. However, when comparing the adsorption on the two metal oxides, the chemical state of the carboxyl group was found to be different. Binding to TiO2 results in four chemically equivalent carboxyl oxygens, while the oxygens are found chemically nonequivalent for adsorption onto ZnO. In addition, information concerning the frontier electronic structure was obtained by measuring the valence band region by PES using different photon energies and the N1s near edge X-ray absorption spectroscopy (NEXAFS) spectra for the two molecules adsorbed on the surfaces.