Light-induced charge separation across Ru(II)-modified nanocrystalline TiO2 interfaces with phenothiazine donors.

Long-lived interfacial charge-separated pairs, [TiO2(e(-)), D+], have been created by visible light excitation of Ru(II) polypyridyl compounds anchored to TiO2 particles in the presence of phenothiazine donors, D. The kinetic aspects of the formation and recombination have been kinetically resolved for analogous colloidal TiO2 solutions and films. Charge-separated pair lifetimes are shortened in colloidal films due to their high local concentrations. Less than 1% incident photon-to-current efficiency is observed when PTZ (phenothiazine) derivatives are employed as donors in regenerative solar cells. Light excitation of Ru(4,4'-(CO2H)(2)-2,2'-bipyridine)(2)(4-CH3,4'-CH2-PTZ-2,2'-bipyridine)](2+) anchored to TiO2, results in rapid intramolecular electron transfer from PTZ to the ruthenium metal center which efficiently translates the hole away from the chromophoric unit to the pendant PTZ group. The net result is the formation of a remarkably long-lived charge-separated pair, TiO2(e(-))\-Ru-II-PTZ(+), that lives for similar to 300 mu s and directly results in an increased open circuit photovoltage when compared to a model compound