Solvent-Polarity Dependence of Electron-Transfer Kinetics in a CdSe/ZnS Quantum Dot−Pyromellitimide Conjugate

Abstract

Photoinduced electron transfer (ET) to and from semiconductor quantum dots (QDs) is of intense interest because of its important roles in QD-based devices, such as detectors, light-emitting diodes, and solar cells. In this study, we have investigated the solvent dependence of the interfacial ET between ZnS-capped CdSe (CdSe/ZnS) QDs and pyromellitimide (PI) at the ensemble and single-particle levels. The steady-state and time-resolved photoluminescence (PL) and absorption measurements revealed that the rates of ET from the excited CdSe/ZnS to the adsorbed PI-CA molecules in nonpolar solvents, such as octane and toluene, are higher than aprotic polar solvents, such as benzonitrile. Furthermore, it was found that two pathways are included in the ET processes between CdSe/ZnS and PI, that is, ET from the excited CdSe core to PI-CA molecules adsorbed on the surface of the CdSe or ZnS. The former process proceeds on the picosecond time scale, while the latter proceeds on the nanosecond time scale. The interfac...