Visible Light Induced Photocleavage of DNA by a Mixed-Metal Supramolecular Complex:  [{(bpy)₂Ru(dpp)}₂RhCl₂]⁵⁺

The mixed-metal supramolecular complex, [{(bpy)₂Ru(dpp)}₂RhCl₂](PF₆)₅ (bpy = 2,2‘-bipyridine and dpp = 2,3-bis(2-pyridyl)pyrazine) coupling two ruthenium light absorbers (LAs) to a central rhodium, has been shown to photocleave DNA. This system possesses a lowest lying metal to metal charge transfer (MMCT) excited state in contrast to the metal to ligand charge transfer states (MLCT) of the bpm and Ir analogues. The systems with an MLCT excited state do not photocleavage DNA. [{(bpy)₂Ru(dpp)}₂RhCl₂](PF₆)₅ is the first supramolecular system shown to cleave DNA. It functions through an excited state previously unexplored for this reactivity, a Ru → Rh MMCT excited state. This system functions when irradiated with low energy visible light with or without molecular oxygen.