The adsorption of dye monolayers on nanocrystalline titanium dioxide surfaces leads to high photoelectrochemical yields in the visible range, which gives a renewal of interest in the use of this system in solar energy. A high resonance effect in these dyes enabled the attainment of the Raman spectra of the adsorbed molecules; further, a new series of Raman peaks appeared during the polarization of TiO2 modified by Ru-bipyridinium compounds in the presence of an electron donor. They correspond to a molecular configuration in which an electron is exchanged during the measurement between a particular ligand and a substrate titanium atom. This configuration appears then to be similar to the short-lived excited state of the metal ligand charge-transfer complex (MLCT).