Sensitization of nanocrystalline TiO2 by Re(I) polypyridyl compounds

The compounds [Re(deeb)(CO)(3)(py)](OTf) and [Re(bpy)(CO)(3)(ina)](OTf), where bpy is 2,2'-bipyridine, (deeb) is 4,4'-(COOEt)(2)-2,2'-bipyridine, (py) is pyridine, (ina) is isonicotinic acid, and OTf is triflate anion have been prepared, characterized, and anchored to nanocrystalline TiO2. The two compounds were designed such that Re(deeb)(CO)(3)(py)(+) is bound to TiO2 through the deeb ligand and the Re(bpy)(CO)(3)(ina)(+) is bound through a non-chromophoric ina ligand. We find that the absorbed photon-to-current efficiencies are, within experimental error, unity at 450 nm for both compounds. Thermodynamically favorable recombination of the injected electron in TiO2 with the oxidized sensitizer requires milliseconds for completion.