Sensitization of nanocrystalline TiO2 by Re(I) polypyridyl compounds

The compounds [Re(deeb)(CO)(3)(py)](OTf) and [Re(bpy)(CO)(3)(ina)](OTf), wh ere 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 be en prepared, characterized, and anchored to nanocrystalline TiO2. The two c ompounds were designed such that Re(deeb)(CO)(3)(py)(+) is bound to TiO2 th rough 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 effic iencies 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.