RESONANCE RAMAN INVESTIGATION OF RU(PHEN)(2)(DPPZ)(2+) AND RELATED COMPLEXES IN WATER AND IN THE PRESENCE OF DNA

Resonance Raman (rR) spectroscopy was utilized to gain insight into th e electronic structure of dppz (dppz = dipyrido[3,2-alpha:2',3'-c]phen azine) complexes of Ru(II) and Os(II). The time-resolved resonance Ram an (TR3) spectrum of Ru(phen)(2)(dppz)(2+) (phen = 1,10-phenanthroline ) collected under 355 nm (fwhm approximate to 10 ns) excitation is con sistent with the population of a ligand-centered (LC) (3) pi pi state of the dppz ligand. Since emission from the Ru(II) --> (dppz) metal-t o-ligand charge transfer (MLCT) excited state is observed, both states must possess similar energies. Lowering of the MLCT state energy in R u(phen)(2)(F-2-dppz)(2+) and Os(phen)(2)(dppz)(2+) with respect to tha t of the (3) pi pi State results in the disappearance of the LC (3) p i pi excited-state peaks in the rR spectrum, indicative of its fast d eactivation to the lower MLCT state in these complexes. addition of DN A to the samples containing Ru(phen)(2)(dppz)(2+) and Ru(phen)(2)(F-2- dppz)(2+) leads to a decrease in intensity of the peaks associated wit h the intercalating phenazine part of the dppz ligand. Further increas e in the DNA:Ru ratio causes broadening of the spectrum. This broadeni ng has been interpreted in terms of strong pi pi interaction between t he intercalated dppz ligand and the DNA bases.