Sensitization of nanocrystalline TiO2 by electropolymerized thin films

Following adsorption of [Ru(vbpy)(2)(dcb)](PF6)(2) (dcb is 2,2'-bipyridine-4,4'-dicarboxylic acid; vbpy is 4-methyl-4'-vinyl-2,2'-bipyridine) on nanocrystalline TiO2 thin films, [Ru(vbpy)(3)](PF6)(2) or [Zn(vbpy)(3)](PF6)(2) can be reductively electropolymerized in acetonitrile. This creates overlayer surface structures stabilized, toward loss of the sensitizer, by cross-surface covalent bonding. Ru(II-->)bpy, metal-to-ligand charge transfer (MLCT) excitation of the resulting thin film structures and photoinjection in two-electrode cells results in incident photon-to-current conversion efficiencies (IPCE), which are dependent on the overlayer structure. This is shown in the photocurrent action spectra below in propylene carbonate 0.5 M in NaI and 0.05 M in I-2: (A) adsorbed [Ru(vbpy)(2)(dcb)](PF6)(2); (B) as in A, but with an overlayer of poly[Zn(vbpy)(3)](PF6)(2); and (C) as in A, but with an overlayer of poly[ru(vbpy)(3)](PF6)(2).