Synthesis of New Ruthenium (II) Bipyridyl Complexes and Studies on Their Photophysical and Photoelectrochemical Properties

Two new mixed-ligand ruthenium(II) complexes, Ru(dcbpy)-(LL) (NCS)2[where dcbpy = 4, 4′-dicarboxyl-2,2′-bipyridine, LL = 4,4′-bis (N-methyl-anilinomethyl)-2,2′-bipyridine (1) or 4-methyl-4′-N-methyl-anilinomethyl-2,2′-bipyridine (2)], were synthesized, and the photophysical properties of these complexes were studied. The metal-to-ligand charge transfer (MLCT) transitions of these complexes exhibited solvatochromic effect due to the existence of NCS ligands. The MLCT energies also strongly depend on the pH values of the solutions because of protonation and deprotonation of the carboxyl groups. The pKa, values of the ground state, 4.0 for 1 and 3.8 for 2, were obtained from the titration curves. The photoelectrochemical properties of 1 and 2 as sensitizers in sandwich-type solar cells have been studied. Complex 1 exhibited better photoelectrochemical behavior than complex 2 as expected. It was proved that the design of mixed-ligand complex by introducing electron donating group in one of the ligands should be a promising approach.