Abstract
UV−visible spectra, emission spectra, and RuIII/II reduction potentials have been measured for cis-[Ru(bpy)2(py)(CN)]+ (bpy is 2,2‘-bipyridine; py is pyridine), cis-Ru(bpy)2(CN)2, [Ru(tpy)(CN)3]- (tpy is 2,2‘:6‘,2‘‘-terpyridine), [Ru(bpy)(CN)4]2-, and [Ru(MQ+)(CN)5]2- (MQ+ is N-methyl-4,4‘-bipyridinium cation) in twelve solvents. The shifts in the metal-to-ligand charge transfer (MLCT) absorption (Eabs) or emission (Eem) band energies with solvent increase linearly with the number of cyano ligands and correlate well with the Gutmann “acceptor number” of the solvent. Intraligand π → π* band energies also correlate with acceptor number, but with only ∼30% of the shifts for the MLCT bands. The solvent dependence arises through mixing of the π → π* transitions with lower energy MLCT transitions. MLCT absorption and emission spectra are convolutions of overlapping vibronic components, and a Franck−Condon analysis of emission spectral profiles for cis-Ru(bpy)2(CN)2* has been used to evaluate the energy gap, E0,...
Published Version
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