Spectral properties of bipyridyl ligands by time-dependent density functional theory

The properties of a series of bipyridyl ligands, which take an active part in numerous inorganic dyes designed for photovoltaic applications, are studied by the means of density functional theory and time-dependent DFT. In particular, the properties of the 2,2′-bipyridine (bpy) ligand and those of the 4,4′-dicarboxy-2,2′-bipyridine (4,4′-dcbpyH2) and 5,5′-dicarboxy-2,2′-bipyridine (5,5′-dcbpyH2) derivatives (in their neutral and anionic forms) were computed. The calculations were carried out in the gas phase and in solution, represented by a continuum. Beyond the good agreement with experimental data, our results show that the carboxylic groups behave as electron-withdrawing groups showing no specific spectral signature.