Variation of DNA photocleavage efficiency for [(TL)2Ru(dpp)]Cl2 complexes where TL=2,2′-bipyridine, 1,10-phenanthroline, or 4,7-diphenyl-1,10-phenanthroline

The complexes [(bpy)(2)Ru(dpp)]Cl-2, [(phen)(2)Ru(dpp)]Cl-2, and [(Ph(2)phen)(2)Ru(dpp)]Cl-2 (where dpp = 2,3-bis(2-pyridyl)pyrazine, bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, Ph(2)phen = 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)(2)Ru(dpp)](2+) systems populate (MLCT)-M-3 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(2)phen respectively. The 3MLCT states and emissions are quenched by O-2, producing a reactive oxygen species. These complexes photocleave DNA with varying efficiencies, [(Ph(2)phen)(2)Ru(dpp)](2+) > [(phen)(2)Ru(dpp)](2+) > [(bpy)(2)Ru(dpp)](2+). The presence of the polyazine bridging ligand will allow these chromophores to be incorporated into larger supramolecular assemblies. (c) 2006 Elsevier Inc. All rights reserved.