New photosensitizers based upon [FeII(L)2(CN)2] and [FeIIL3], where L is substituted 2,2′-bipyridine

Ultrafast electron transfer in the dye sensitized solar cell (DSSC) has made it possible to use iron(II) polypyridyl complexes as photosensitizers [J. Am. Chem. Soc. 120 (1998) 843]. Although ruthenium(II) polypyridyl complexes comprise an extensively studied and widely utilized photochemical system, comparatively little is known about the photoproperties of their iron analogues. The syntheses and solution properties of the complexes [FeII(L)2(CN)2] and [FeIIL3] for a series of L, where L is a 2,2′-bipyridine derivative, are presented here. We compare the solvatochromism of [FeII(4,4′-dicarboxylic acid-2,2′-bipyridine)2(CN)2] to [FeII(4,4′-dimethyl-2,2′-bipyridine)2(CN)2] and discuss general trends in the electrochemistry and absorption properties within the series. The solvatochromism of these complexes is discussed in terms of their use in a dye sensitized TiO2 solar cell.