Abstract

Transient resonance Raman (TR²) spectroscopy has been used to investigate the metalligand charge-transfer (MLCT) excited states of Ru(II) polypyridyl complexes inDNAand in homogeneous solution. In DNA, complexes of the type [Ru(L)₂(L′)]²⁺ were studied, where L=2, 2^’-bipyridyl (bpy), 1,4, 5, 8-tetraazaphenanthrene (tap), and L′ dipyrido [3,2:a-2′ ,3′:c]-phenazine (dppz) or 1,4,5,8,9,12-hexaazatriphenylene (HAT). For [Ru(bpy)₂(HAT)]²⁺, the enhancement pattern of vibrational modes in the TR² spectra attributable to reduced HAT⋅− in the triplet MLCT state suggest perturbations to the intraligand transition of HAT⋅− in the presence of DNA. Transient RR spectra for [Ru(tap)₂(dppz)]²⁺ are indicative of formation of the species Run^II(tap⋅−)(tap)(dppz) by electron transfer from DNA to the triplet MLCT state of the complex.TR² spectra for complexes of the type, [(Ru(bpy)2)n(L)]2+ , n=1, 2 where L=a triazole bridging ligand, illustrate the use of the technique as a probe of the response of MLCT states to the electronic environment.