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

An alternative mechanism for dye sensitization of Ride bandgap semiconductors has been realized: reductive quenching of the dye excited state(s) followed by thermal interfacial electron transfer. The processes were identified using nanosecond-time-resolved absorption and photoluminescence spectroscopies 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 anchored to a nanocrystalline (anatase) TiO2 film immersed in a 0.1 M tetrabutylammonium perchlorate acetonitrile solution with phenothiazine electron donors. With the electrolyte changed to 0.1 M lithium perchlorate, this same 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.