ORIGIN OF NEW BANDS IN THE RAMAN-SPECTRA OF DYE MONOLAYERS ADSORBED ON NANOCRYSTALLINE TIO2

The adsorption of dye monolayers on nanocrystalline titanium dioxide s urfaces 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 cor respond to a molecular configuration in which an electron is exchanged during the measurement between a particular ligand and a substrate ti tanium atom. This configuration appears then to be similar to the shor t-lived excited state of the metal ligand charge-transfer complex (MLC T).