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)₂Ru(dpp)]Cl₂, [(phen)₂Ru(dpp)]Cl₂, and [(Ph₂phen)₂Ru(dpp)]Cl₂ (where dpp = 2,3-bis(2-pyridyl)pyrazine, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, Ph₂phen = 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 Ph₂phen respectively. The ³MLCT states and emissions are quenched by O₂, producing a reactive oxygen species. These complexes photocleave DNA with varying efficiencies, [(Ph₂phen)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.