Vibrational and Electronic Spectroscopy of Electronically Excited Polychromophoric Ruthenium(II) Complexes

Abstract

The metal to ligand charge-transfer excited states of the polychromophoric complexes [(NC)-(bpy)[sub 2]Ru[sup II](CN)Ru[sup II](bpy)[sub 2](CN)][sup +], [(NC)(bpy)[sub 2]Ru[sup II](CN)Ru[sup II](phen)[sub 2](CN)][sup +], [(NC)(phen)[sub 2]Ru[sup II](CN)Ru[sup II](bpy)[sub 2](CN)][sup +], [(NC)(bpy)[sub 2]Ru[sup II](CN)Ru[sup II](bpy)[sub 2](NC)Ru[sup II](bpy)[sub 2](CN)][sup 2+], and [NC(bpy)[sub 2]Ru[sup II](CN)Ru[sup II](dcb)[sub 2](NC)Ru(bpy)[sub 2](CN)][sup 2[minus]] (bpy is 2,2[prime]-bipyridine, phen is 1,10-phenanthroline, and dcb is 4,4[prime]-dicarboxy-2,2[prime]-bipyridine) and of model mononuclear complexes have been investigated in CH[sub 3]CN by time-resolved resonance Raman (TR[sup 3]) and transient UV/vis absorption spectroscopy. The observation in the TR[sup 3] spectra of vibrations of a single type of reduced ligand and the cross check obtained by exchanging ligands around the metal centers provide unambiguous evidence for localization of the excited electron on the polypyridine ligand of the N-bonded (to bridging CN[sup [minus]]) chromophore. The presence of excited-state intervalence transfer bands has been inferred by the comparison of the transient absorbance spectra of the polynuclear complexes with the ground-state spectra to reduced and one-electron oxidized forms and with the spectra of the excited mononuclear complexes. These comparisons indicate the presence of distinct Ru(II) and Ru(III) centers in the excited states of the polynuclear complexes.