Transient Resonance Raman Studies of Ru(II) Complexes in DNA and in Homogeneous Media

Transient resonance Raman (TR 2 ) spectroscopy has been used to investigate the metalligandcharge-transfer (MLCT) excited states of Ru(II) polypyridyl complexes inDNAandin 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 TR 2 spectraattributable to reducedHAT ⋅ −in the triplet MLCT state suggest perturbations to theintraligand transition ofHAT ⋅ −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) byelectron transfer from DNA to the triplet MLCT state of the complex. TR 2 spectra for complexes of the type,[( Ru( bpy ) 2 ) n ( L ) ]2 +, n=1, 2 where L=a triazolebridging ligand, illustrate the use of the technique as a probe of the response of MLCTstates to the electronic environment.