New photosensitizers based upon [Fe(L)(2)(CN)(2)] and [Fe(L)(3)](L = substituted 2,2 '-bipyridine): Yields for then photosensitization of TiO2 and effects on the band selectivity

Our recent report of the sensitization of TiO2 by [Fe(4,4'-dicarboxylic aci d-2,2'-bipyridine)(2)(CN)(2)] introduced iron(II) bipyridyl complexes as fu ndamentally interesting and practical alternatives to their ruthenium analo gues in the dye-sensitized solar cell (Ferrere and Gregg, J. Am. Chem. Sec. 1998, 120, 843). Here we detail how structural changes to the bipyridyl li gand L in [Fe(L)(2)(CN)(2)] affect photosensitization yields. We also explo re the effect of solvent and solvent additives on the unique absorbance ban d selectivity of [Fe(4,4'-dicarboxylic acid-2,2'-bipyridine)(2)(CN)(2)] on TiO2. We demonstrate that solvent conditions can affect the relative photoc urrent contributions from the two absorption bands of the complex, and sugg est that it is related to changes in driving force for electron injection f rom the lower energy MLCT band.