VIBRATIONAL AND ELECTRONIC SPECTROSCOPY OF ELECTRONICALLY EXCITED POLYCHROMOPHORIC RUTHENIUM(II) COMPLEXES

The metal to ligand charge-transfer excited states of the polychromoph oric complexes [(NC-(bpy)2Ru(II)(CN)Ru(II)(bpy)2(CN)]+, [(NC)(bpy)2Ru( II)(CN)Ru(II)(Phen)2(CN)]+, [(NC)(Phen)2Ru(II)(CN)Ru(II)(bpy)2(CN)]+, py)2Ru(II)(CN)Ru(II)(bpy)2(NC)Ru(II)(bpy)2(CN)]2+, and [NC(bpy)2Ru(II) (CN)Ru(II)(dcb)2(NC)Ru( bpy)2(CN)]2- (bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline, and dcb is 4,4'-dicarboxy-2,2'-bipyridine) and of model mononuclear complexes have been investigated in CH3CN by time-r esolved resonance Raman (TR3) and transient UV/vis absorption spectros copy. The observation in the TR3 spectra of vibrations of a single typ e of reduced ligand and the cross check obtained by exchanging ligands around the metal centers provide unambiguous evidence for localizatio n of the excited electron on the polypyridine ligand of the N-bonded ( to bridging CN-) chromophore. The presence of excited-state intervalen ce transfer bands has been inferred by the comparison of the transient absorbance spectra of the polynuclear complexes with the ground-state spectra of reduced and one-electron oxidized forms and with the spect ra of the excited mononuclear complexes. These comparisons indicate th e presence of distinct Ru(II) and Ru(III) centers in the excited state s of the polynuclear complexes.