Synthesis and Photochemical Properties of Novel Ruthenium(II)-Nickel(II) and Ruthenium(II)-Copper(II) Dinuclear Complexes

Novel Ru(II)-Ni(II) and Ru(II)-Cu(II) dinuclear complexes have been synthesized and characterized. In these complexes, the ruthenium(II) polypyridyl group and the Ni(II)- or Cu(II)-Schiff base units are fused together by a bridging ligand, 5,6-di(salicylidenamino)-1,10-phenanthroline. X-ray crystallography on the Ru(II)-Ni(II) dinuclear complex shows that the Ni(II)-Schiff base unit is distorted against the plane of the phenanthroline ring due to the effect of a steric repulsion between the phenanthroline ring and the Ni(II)-Schiff base unit. The properties of the excited states of the dinuclear complexes are discussed by comparing them with that of the Ru(II)-Zn(II) analogue as a reference compound. These complexes show the emission from the excited state, which is assigned to MLCT0 (the excited state due to the transition from Ru(II) to the bridging ligand). For the Ru(II)-Cu(II) complex, the lifetime of the emission is found to be 80 ns, which is identical to that of the Ru (II)-Zn(II) analogue, suggesting that no quenching process exists. On the contrary, for the Ru(II)-Ni(II) complex, the emission decays very rapid. The energy transfer to the Ni(II)-Schiff base unit deactivates the MLCT0 excited state.