Sensitization of nanocrystalline TiO2 initiated by reductive quenching of molecular excited states

An alternative mechanism for dye sensitization of Ride bandgap semiconducto rs has been realized: reductive quenching of the dye excited state(s) follo wed by thermal interfacial electron transfer. The processes were identified using nanosecond-time-resolved absorption and photoluminescence spectrosco pies after selective excitation of Ru(deeb)(bpy)(2)(PF6)(2), where bpy is 2 ,2'-bipyridine and deeb is 4,4'-(COOC2H5)(2)-2,2'-bipyridine, sensitizers a nchored to a nanocrystalline (anatase) TiO2 film immersed in a 0.1 M tetrab utylammonium perchlorate acetonitrile solution with phenothiazine electron donors. With the electrolyte changed to 0.1 M lithium perchlorate, this sam e assembly undergoes the generally accepted mechanism for dye sensitization : the sensitizer excited state(s) transfer an electron to the semiconductor and is subsequently reduced by the phenothiazine donor.