Enhancement of quantum yield and lifetime of photoinduced chargeseparation for cyclometallated platinum(II) complex/ferricyanide system via Nafion membrane-solution interface

Abstract

The photoinduced electron transfer from the excited state of cyclometallated platinum(II) complex PtL1L2 2+ (L1=4-methoxyphenyl-6-phenyl-2,2′-bibyridine, L2=pyridine) incorporated into Nafion membranes to Fe(CN)6 3− in the surrounding solution has been examined. N,N′-tetramethylene-2,2′-bipyridinium (DQ2+) entrapped in the Nafion membranes is used as an electron relay. Luminescence quenching studies indicate that the quenching reaction of the excited PtL1L2 2+ with DQ2+ is static in nature. PtL1L2 3+ generated from the luminescence quenching remains in the Nafion matrix, while DQ+ migrates by an electron hopping mechanism to the Nafion-water interface, where transfers an electron to Fe(CN)6 3− to produce Fe(CN)6 4−. The negatively charged Fe(CN)6 4− is repelled into the bulk solution by the anionic Nafion surface. The isolation of the photoinduced oxidized species PtL1L2 3+ in Nafion from the ultimate reduced species Fe(CN)6 4− in solution prevents them from undergoing back electron transfer. Thus, an extremely long-lived charge separation state is achieved in a high quantum yield.