The synthesis and characterization of a family of piano-stool Ru II arene complexes of the type [(η 6 -arene)Ru(N,N')(L)] [PF 6 ] 2 where arene is para-cymene (p-cym), hexamethylbenzene (hmb) or indane (ind); N,N' is 2,2'-bipyrimidine (bpm), 1,10-phenanthroline (phen), 1,10-phenanthroline-5,6-dione (phendio), 4,7-diphenyl-1,10-phenanthroline (bathophen), and L is pyridine (Py), 4-methylpyridine (4-MePy), 4-methoxypyridine (4-MeOPy), 4,4'-bipyridine (4,4'-biPy), 4-phenylpyridine (4-PhPy), 4-benzylpyridine (4-BzPy), 1,2,4-triazole (trz), 3-acetylpyridine (3-AcPy), nicotinamide (NA), or 3-acetatepyridine (3-AcOPy) are reported; including the X-ray crystal structures of [(η 6 -p-[(η 6 -p-cym)Ru(phen)(Py)] 2+ (10), and [(η 6 -ind)Ru(bpy)(Py)] 2+ (13). These complexes can selectively photodissociate the monodentate ligand (L) when excited with UVA or white light allowing strict control of the formation of the reactive aqua species [(η 6 -arene)Ru(N,N')(OH 2 )] 2+ that otherwise would not form in the dark. The photoproducts were characterized by UV-vis absorption and 1 H NMR spectroscopy. DFT and TD-DFT calculations were employed to characterize the excited states and to obtain information on the photochemistry of the complexes. All the Ru II pyridine complexes follow a relatively similar photochemical L-ligand dissociation mechanism, likely to occur from a series of 3 MC triplet states with dissociative character. The photochemical process proved to be much more efficient when UVA-range irradiation was used. More strikingly, light activation was used to photo-trigger binding of these potential anticancer agents with discriminating preference towards 9-ethylguanine (9-EtG) over 9-ethyladenine (9-EtA). Calf-thymus (CT)-DNA binding studies showed that the irradiated complexes bind to CT-DNA whereas the non-irradiated forms, bind negligibly.
