Ligand-Specific Charge Localization in the MLCT Excited State of Ru(bpy)_2(dpphen)^(2+) Monitored by Time-Resolved Resonance Raman Spectroscopy
Time-resolved resonance Raman spectroscopy has been employed to examine the location of the promoted electron in the metal-to-ligand charge-transfer (MLCT) excited state of Ru(bpy)_2(dpphen)^(2+) (bpy) = 2,2'-bipyridine; dpphen = 4,7-diphenyl-1,10-phenanthroline). Variations in the environment about Ru(bpy)_2(dpphen)^(2+) shift the localization of charge in the MLCT excited state from bpy in neutral micelles (Brij 35) to dpphen in the presence of DNA and anionic surfactants (C_(12)H_(25)OSO_3Na, C_(10)H_(23)OSO_3Na, and C_8H_(21)OSO_3Na), whereas in water the electron is localized on both ligands. The shifts in the electronic absorption spectrum and the dependence of the ground-state resonance Raman (rR) signal with excitation wavelengths coincident with the high- and low-energy sides of the MLCT absorption band are consistent with a lowering of the energy of the Ru(II)-dpphen transition with respect to that of bpy in anionic micelles.
© 1994 American Chemical Society. Received May 7, 1993. C.T. thanks the Jane Coffin Childs Memorial Fund for Medical Research for a fellowship. This investigation was aided by a grant from the Jane Coffin Childs Memorial Fund for Medical Research. Further support was provided by the Deutsche Forschungsgemeinschaft (S.H.B.) and the National Institutes of Health (G.E.L.). N.J.T. thanks the National Science Foundation and J.K.B. thanks the NIH for generous support of this research. We thank the MSU LASER Laboratory for use of facilities to collect CW resonance Raman spectra.