Vibrational Spectra, Normal Coordinate Analysis and Excited-State Lifetimes for a Series of Polypyridylruthenium(II) Complexes

Surface-enhanced (resonance) Raman scattering [SE(R)RS] spectra of five mixed-ligand RuII complexes were recorded and analysed in detail by comparison with the spectrum of Ru(bpy)3 (bpy=bipyridine) and the results of a normal-mode calculation for the ligands bipyridine and terpyridine. For the latter calculations the program package VAMP 5.5 was modified to scale down the force field for the second-row elements. With this procedure, fairly good agreement between calculated and observed wavenumbers could be achieved. It is shown that the SER(R)S spectrum of the mixed complexes with terpyridine are dominated by the contributions of terpyridine whose MLCT (metal-to-ligand charge-transfer) transition is in near-resonance with the exciting radiation. The interaction between terpyridine and the other ligands is reflected not only in the intensity distribution of the SER(R)S spectra, but also in the excited-state lifetimes.