Variation of DNA photocleavage efficiency for [(TL) 2Ru(dpp)]Cl 2 complexes where TL = 2,2′-bipyridine, 1,10-phenanthroline, or 4,7-diphenyl-1,10-phenanthroline

Abstract

The complexes [(bpy) 2Ru(dpp)]Cl 2, [(phen) 2Ru(dpp)]Cl 2, and [(Ph 2phen) 2Ru(dpp)]Cl 2 (where dpp = 2,3-bis(2-pyridyl)pyrazine, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, Ph 2phen = 4,7-diphenyl-1,10-phenanthroline) have been investigated and found to photocleave DNA via an oxygen-mediated pathway. These light absorbing complexes possess intense metal-to-ligand charge transfer (MLCT) transitions in the visible region of the spectrum. The [(TL) 2Ru(dpp)] 2+ systems populate 3MLCT states after visible light excitation, giving rise to emissions in aqueous solution centered at 692, 690, and 698 nm for TL = bpy, phen, and Ph 2phen respectively. The 3MLCT states and emissions are quenched by O 2, producing a reactive oxygen species. These complexes photocleave DNA with varying efficiencies, [(Ph 2phen) 2Ru(dpp)] 2+ > [(phen) 2Ru(dpp)] 2+ > [(bpy) 2Ru(dpp)] 2+. The presence of the polyazine bridging ligand will allow these chromophores to be incorporated into larger supramolecular assemblies.