Transient resonance Raman studies of Ru(II) complexes in DNA and in homogeneous media

Abstract

Transient resonance Raman (TR2) spectroscopy has been used to investigate the metal-ligand charge-transfer (MLCT) excited states of Ru(II) polypyridyl complexes in DNA and 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 RuII(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 = atriazole bridging ligand, illustrate the use of the technique as a probe of the response of MLCT states to the electronic environment. © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint, part of The Gordon and Breach Publishing Group.