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 compoun ds anchored to TiO2 particles in the presence of phenothiazine donors, D. The kinetic aspects of the formation and recombination have been k inetically resolved for analogous colloidal TiO2 solutions and films. Charge-separated pair lifetimes are shortened in colloidal films due t o their high local concentrations. Less than 1% incident photon-to-cur rent efficiency is observed when PTZ (phenothiazine) derivatives are e mployed as donors in regenerative solar cells. Light excitation of yri dine)(2)(4-CH3,4'-CH2-PTZ-2,2'-bipyridine)](2+) anchored to TiO2, resu lts in rapid intramolecular electron transfer from PTZ to the rutheniu m metal center which efficiently translates the hole away from the chr omophoric unit to the pendant PTZ group. The net result is the formati on 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 .