FAST PHOTOINDUCED ELECTRON-TRANSFER THROUGH DNA INTERCALATION

We report evidence for fast photoinduced electron transfer mediated by the DNA helix that requires metal complexes that are avid intercalato rs of DNA. Here the donor bis(phenanthroline) (dipyridophenazine)ruthe nium(II) [Ru(phen)(2)dppz(2+)] and acceptor bis(9,10-phenanthrenequino ne diimine)(phenanthroline)rhodium(III) [Rh(phi)(2)phen(3+)] intercala te into DNA with K-b > 10(6) M(-1) Luminescence quenching experiments in the presence of two different lengths of DNA yield upward-curving S tern-Volmer plots and the loss of luminescence intensity far exceeds t he change in emission lifetimes. In the presence of a nonintercalative electron acceptor, Ru(NH3)(6)(3+), Ru(phen)(2)dppz(2+) luminescence i s quenched much less efficiently compared to that found for the interc alative Rh(phi)(2)phen(3+) quencher and follows linear Stern-Volmer ki netics; steady-state and time-resolved Stern-Volmer plots are comparab le in scale. These experiments are consistent with a model involving f ast long-range electron transfer between intercalators through the DNA helix.