Absorption and electrochemical properties of ruthenium(II) dyes, studied by semiempirical quantum chemical calculations

The electronic properties of Ru-polypyridine dyes were investigated by means of semiempirical calculations. Intermediate neglect of differential overlap (INDO)/S including configuration interaction (CI) was used to calculate electronic density of state (DOS) structures, transition energies and oscillator strengths. Results for electronic transitions and HOMO energies were compared to absorption spectra and oxidation potentials. The carboxylated form of cis-bis(2,2'-bipyridine)bis(isothiocyanato)-ruthenium(II) is an efficient sensitizer in nanostructured photoelectrochemical solar cells. The calculation on this dye reveals a different electronic structure for this complex compared to the other Ru-polypyridine complexes. In this complex, the spatial distribution of the highest occupied molecular orbital is shifted towards the NCS ligands and the electronic transition lowest in energy is assigned to a RuNCS-bpy(pi*) charge transfer transition. (C) 1998 Elsevier Science S.A. All rights reserved.