Efficient Light-Driven Oxidation of Alcohols Using an Organic Chromophore-Catalyst Assembly Anchored to TiO2

The ligand 5-PO3H2-2,2':5',2 ''-terthiophene-5-trpy, T3 (trpy = 2,2':6',2 ''-terpyridine), was prepared and studied in aqueous solutions along with its metal complex assembly [Ru(T3)(bpy)(OH2)](2+) (T3-Ru-OH2, bpy = 2,2'-bipyridine). T3 contains a phosphonic acid group for anchoring to a TiO2 photoanode under aqueous conditions, a terthiophene fragment for light absorption and electron injection into TiO2, and a terminal trpy ligand for the construction of assemblies comprising a molecular oxidation catalyst. At a TiO2 photoanode, T3 displays efficient injection at pH 4.35 as evidenced by the high photocurrents (similar to 350 uA/cm(2)) arising from hydroquinone oxidation. Addition of [Ru(bpy)(OTf)][OTf](2) (bpy = 2,2'-bipyridine, OTf- = triflate) to T3 at the free trpy ligand forms the molecular assembly, T3-Ru-OH2, with the oxidative catalyst fragment: [Ru(trpy)(bpy)(OH2)](2+). The new assembly, T3-Ru-OH2, was used to perform efficient light-driven oxidation of phenol (230 mu A/cm(2)) and benzyl alcohol (25 mu A/cm(2)) in a dye sensitized photoelectrosynthesis cell.