[Ru(TAP)2(dppz)]2+: a DNA intercalating complex, which luminesces strongly in water and undergoes photo-induced proton-coupled electron transfer with guanosine-5′-monophosphate
The lowest excited state of [Ru(TAP)2(dppz)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene, dppz = dipyrido[3,2-a:2′,3′-c]phenazine) 1 is strongly luminescent, even in water, and very oxidizing. Therefore it is able to oxidise not only guanosine-5′-monophosphate (GMP), as demonstrated by laser flash photolysis, but also guanine-containing polynucleotides such as calf thymus DNA and [poly(dG–dC)]2. The luminescence quenching was found to be faster in H2O than in D2O, as is the back reaction, indicating that both processes probably proceed by proton-coupled electron transfer. These properties, that are controlled by the triplet MLCT state in which the charge has been transferred from the Ru to a TAP ligand, contrast with those of the well known [Ru(phen)2(dppz)]2+2.