Picosecond Raman measurements of electron transfer in the metal-to-ligand charge-transfer excited states of (1,10-phenanthroline)ruthenium(II) complexes

Picosecond time-resolved resonance Raman spectroscopy has been utilized to investigate the metal-to-ligand charge-transfer (MLCT) excited states of Ru(II) mixed ligand complexes of 1,10-phenanthroline and 2,2′-bipyridine. A two-color pump and probe technique is shown to provide a powerful method for separating the highly congested spectra of these complexes. The first pure excited-state spectrum of [Ru(phen)3]2+ has been obtained. It is clearly demonstrated by using this approach that the interpretation of previous nanosecond Raman results on similar complexes is incorrect with respect to the assignments of the electronic-state parentage of the observed vibrational bands. The implications of these results are discussed with respect to the dynamics of interligand electron transfer in the excited MLCT state.