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

A new series of ruthenium(II) polypyridyl sensitizers with strongly electro n 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-dimercaptoacrylat e (ecda) or 1,2-b enzenedithiolate (bdt) or 3,4-toluenedithiolate (tdt), dc bpy is 4,4'-dicarboxy-2,2-bipyridine, and dcphen is 4,7-dicarboxy-1,10-phen anthroline have been prepared for sensitization of nanocrystalline TiO2 ele ctrodes. All the complexes exhibit a broad metal-to-ligand charge transfer absorption band over the whole visible range. The low-energy absorption ban ds and the Ru(II)/(III) oxidation potentials in these complexes could be tu ned to about 150 nm and 600 mV, respectively, by choosing appropriate dithi olate ligands. When anchored to nanocrystalline titanium dioxide electrodes for light to electrical energy conversion in regenerative photoelectrochem ical cells with I-/I-3(-) acetonitrile electrolyte, these complexes show di fferent sensitization to TiO2 electrodes with increasing activity in the se quence L = tdt, bdt, ecda, qdt. Both Ru(dcbpy)(2)(qdt) and Ru(dcphen)(2)(qd t) 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) 200 1 Elsevier Science B.V. All rights reserved.