Separation of linkage isomers of trithiocyanato (4,4',4"-tricarboxy-2,2',6,2"-terpyridine)ruthenium(II) by pH-titration method and their application in nanocrystalline TiO2-based solar cells

A new series of panchromatic ruthenium(H) sensitizers derived from carboxylated terpyridyl complexes of tris-thiocyanato Ru(H) have been developed. The Link-age isomers {(C4H9)(4)N}(3)[Ru(Htcterpy)(-NCS)(3)] 1, {(C4H9)(4)N}(3)[Ru(Htcterpy)(-NCS)(2)(-SCN)] 2 and {(C4H9)(4)N}(3)[Ru(Htcterpy)(-SCN)(3)] 3 have been separated by pH titration method and fully characterized by UV-Vis, emission, IR and NMR studies. The absorption and emission maxima of the isomer 1 show a bathochromic shift with decreasing pH, and exhibit pH-dependent excited state lifetimes. The red-shift of the emission maxima is due to better pi -acceptor properties of the acid form that lowers the energy of the CT excited state. The isomer 1, when anchored to nanocrystalline TiO2 films achieves very efficient sensitization over the whole visible range extending into the near IR region up to 920 nm, yielding over 80% incident photon-to-current conversion efficiencies (IPCEs). Solar cells containing the isomer 1 were subjected to analysis by a photovoltaic calibration laboratory (NREL, USA) to determine their solar to electric conversion efficiency under standard AM 1.5 sunlight. A short circuit photocurrent density obtained was 20.5 mA/cm(2) and the open circuit voltage was 0.72 V corresponding to an overall conversion efficiency of 10.4%. (C) 2001 Elsevier Science B.V. All rights reserved.