The light switch effect upon the association of [Ru(1,10-phenanthroline)2dipyrido[3,2-a:2′,3′-c]phenazine]2+ with single stranded poly(dA) and poly(dT)

Large enhancement in the luminescence intensity of the Δ- and Λ-Ru(phenanthroline)2dipyrido[3,2-a:2′,3′-c]phenazine]2+ ([Ru(phen)2DPPZ]2+) complexes upon their association with single stranded poly(dA) and poly(dT) is reported in this work. As the mixing ratio ([[Ru(phen)2DPPZ]2+]/[DNA base]) increases, the luminescence intensity increase in a sigmoidal manner, indicating that the enhancement involves some cooperativity. At a high mixing ratio, the luminescence properties are affected by the nature of the DNA bases and not by the absolute configuration of the [Ru(phen)2DPPZ]2+ complex, indicating that the single stranded poly(dA) and poly(dT) do not recognize the configuration of the metal complex. In the case of the Λ-[Ru(phen)2DPPZ]2+–poly(dT) complex, the manner of the enhancement is somewhat different from the other Ru(II) complex–polynucelotide combinations: the luminescence intensity reached a maximum at an intermediate mixing ratio of 0.32, and gradually decreased as the mixing ratio increased. In contrast to other complexes at high mixing ratios, an upward bending curve was found in the Stern–Volmer plot, which indicates that the micro-environment of the Λ-[Ru(phen)2DPPZ]2+ is heterogeneous. In the Δ-[Ru(phen)2DPPZ]2+–poly(dT) complex case, formation of this highly luminescent species at an intermediate mixing ratio is far less effective.