Synthesis and spectroscopic properties of a new bipyridine-bipyrazoyl(pyridine)-thiocyanato-ruthenium(II) complex

Abstract

The complex [Ru(II)(dcbpyH 2)(bdmpp)NCS](PF 6) ( 1) (where dcbpyH 2 is 2,2′-bipyridine-4,4′-dicarboxylic acid, bdmpp is 2,6-bis(3,5-dimethyl- N-pyrazoyl)pyridine,) is synthesized and characterized extensively by 1H NMR and 13C NMR 1D and 2D, mass spectroscopy, cyclic voltammetry, electronic absorption spectroscopy and IR. The half-wave potential of the Ru(II)/Ru(III) redox couple was measured at E 1/2=+0.795 V versus Ag/AgCl in CH 3CN. The complex presents three intense metal-to-ligand charge transfer (MLCT) (d M→π L*) absorption bands centered at 383 ( ε=21 300 M −1 cm −1), 432 ( ε=22 400 M −1 cm −1) and 475 nm ( ε=23 400 M −1 cm −1), respectively. The absorbance is extremely strong between 400 and 500 nm and even at 620 nm, the extinction coefficient is still high ( ε=3768 M −1 cm −1). The strong π-acceptor property of the trans-isothiocyanate ligand compared with the Cl − ligand is probably the cause of the blue-shift observed in complex 1. These properties make the complex potentially promising for the photosensitization process. The incorporation of TiO 2 photoelectrodes derivatized with this complex into a solar cell using a composite polymer/inorganic oxide solid-state electrolyte confirmed its sensitizing ability. Incident monochromatic photon-to-current conversion efficiency (IPCE) values of about 30% and overall energy conversion efficiency ( η) of 1.7% were obtained.