Sensitization of nanocrystalline TiO2 film by ruthenium(II) diimine dithiolate complexes

A new series of ruthenium(II) polypyridyl sensitizers with strongly electron donating dithiolate ligands Ru(dcbpy)(2)(L) and Ru(dcphen)(2) (L) where L is quinoxaline-2,3-dithiolate (qdt) or ethyl-2-cyano-3,3-dimercaptoacrylate (ecda) or 1,2-b enzenedithiolate (bdt) or 3,4-toluenedithiolate (tdt), dcbpy is 4,4'-dicarboxy-2,2-bipyridine, and dcphen is 4,7-dicarboxy-1,10-phenanthroline have been prepared for sensitization of nanocrystalline TiO2 electrodes. All the complexes exhibit a broad metal-to-ligand charge transfer absorption band over the whole visible range. The low-energy absorption bands and the Ru(II)/(III) oxidation potentials in these complexes could be tuned to about 150 nm and 600 mV, respectively, by choosing appropriate dithiolate ligands. When anchored to nanocrystalline titanium dioxide electrodes for light to electrical energy conversion in regenerative photoelectrochemical cells with I-/I-3(-) acetonitrile electrolyte, these complexes show different sensitization to TiO2 electrodes with increasing activity in the sequence L = tdt, bdt, ecda, qdt. Both Ru(dcbpy)(2)(qdt) and Ru(dcphen)(2)(qdt) show overall cell efficiency (eta) of about 3-4%, due to incident photon to current conversion efficiency of around 40-45% at 500 mn. The low cell efficiency of ecda complexes may be due to slow regeneration of the dye by electron donation from iodide following charge injection into TiO2. (C) 2001 Elsevier Science B.V. All rights reserved.