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

The complex [Ru(II)(dcbpyH(2))(bdmpp)NCS](PF6) (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 H-1 NMR and C-13 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 CH3CN. The complex presents three intense metal-to-ligand charge transfer (MLCT) (d(M) --> pi*(L) absorption bands centered at 383 (epsilon = 21300 M-1 cm(-1)), 432 (epsilon = 22 400 M-1 cm(-1)) and 475 nm (epsilon = 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 (epsilon = 3768 M-1 cm(-1)). The strong pi-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 TiO2 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 (eta) of 1.7% were obtained. (C) 2002 Elsevier Science Ltd. All rights reserved.