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 acid-2,2'-bipyridine)(2)(CN)(2)] introduced iron(II) bipyridyl complexes as fundamentally interesting and practical alternatives to their ruthenium analogues 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 ligand L in [Fe(L)(2)(CN)(2)] affect photosensitization yields. We also explore the effect of solvent and solvent additives on the unique absorbance band selectivity of [Fe(4,4'-dicarboxylic acid-2,2'-bipyridine)(2)(CN)(2)] on TiO2. We demonstrate that solvent conditions can affect the relative photocurrent contributions from the two absorption bands of the complex, and suggest that it is related to changes in driving force for electron injection from the lower energy MLCT band.