Redox, spectroscopic, photo-induced ligand exchange, and DNA interaction studies of a new Ru(II)Pt(II) bimetallic complex

A new bimetallic complex, [Ru(biq)2(dpp)PtCl2](PF6)2 (where biq = 2,2′-biquinoline and dpp = 2,3-bis(2-pyridyl)pyrazine), containing a cis-PtCl2 moiety coupled to a sterically strained Ru(II)-based chromophore was designed, synthesized, and investigated with respect to its spectroscopic, redox, photo-induced ligand exchange, and DNA-interaction properties. The electrochemistry of the designed complex was found to be consistent with the bridging coordination of the dpp ligand and formation of the bimetallic complex. The complex displays intense ligand-based π → π* transitions in the UV region and metal-to-ligand charge-transfer transitions (MLCT) in the visible region. The loss of bridging coordination of the dpp ligand and formation of complexes, [Ru(biq)2(CH3CN)2]2+ and [Pt(dpp)(CH3CN)2]2+ was observed when an acetonitrile solution of the metal complex was irradiated with visible light (λirr ≥ 550 nm). The designed complex displays covalent binding with DNA in dark through the cis-PtCl2 moiety, as confirmed by agarose gel electrophoresis. Upon photoirradiation, the complex dissociates into two DNA-binding moieties and displays covalent binding through: (i) a cis-PtL2 subunit of [Ptdpp(L)2]2+ and (ii) open coordination sites of the ruthenium of [Ru(biq)2(L)2]2+ (L = solvent). The designed complex represents the first Ru(II)Pt(II) complex that undergoes photo-induced ligand exchange and displays multifunctional interactions with DNA upon photoirradiation.