Efficient and Selective Photogeneration of Stable N-Centered Radicals via Controllable Charge Carrier Imbalance in Cesium Lead Halide Nanocrystals

Abstract

Despite the versatility of semiconductornanocrystals (NCs) inphotoinduced chemical processes, the generation of stable radicalshas been more challenging due to reverse charge transfer or chargerecombination even in the presence of sacrificial charge acceptors.Here, we show that cesium lead halide (CsPbX3) NCs canselectively photogenerate either aminium or aminyl radicals from amines,taking advantage of the controllable imbalance of the electron andhole populations achieved by varying the solvent composition. Usingdihalomethane as the solvent, irreversible removal of the electronsfrom CsPbX3 NCs enabled by the photoinduced halide exchangebetween the NCs and the dihalomethane resulted in efficient oxidativegeneration of the aminium radical. In the absence of dihalomethanein solvent, the availability of both electrons and holes resultedin the production of an aminyl radical via sequential hole transferand reductive N-H bond dissociation. The negative charge ofthe halide ions on the NC's lattice surface appears to facilitatethe aminyl radical production, competing favorably with the reversiblecharge transfer reverting to the reactant.