Picosecond Raman scattering study of electron localization in the charge transfer excited state of tris(bipyridine)ruthenium (ll).

The localization and relaxation kinetics of the optically excited electron are probed as a function of the chemical nature and rigidity of the solvent. We investigate whether a significant excited state solvation energy is necessary to localize the electron on one ligand. The picosecond time resolved resonance Raman spectra of the lowest metal-to-ligand-charge-transfer excited state have been observed in room temperature water and isopropanol, in 4:1 ethanol/methanol above and below the glass transition temperature, and in anionic micelles. In all cases the excited electron is localized on one bipyridine ligand. The vibrational relaxation - localization process appears to be complete within a few picoseconds. A broadening of MLCT Raman lines at high field intensities is attributed to nonlinear resonance scattering. Localization and subsequent electron hopping are discussed using the simple Franck-Condon electron transfer model for weakly coupled, mixed valence compounds.