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

Abstract

Despite the versatility of semiconductor nanocrystals (NCs) in photoinduced chemical processes, the generation of stable radicals has been more challenging due to reverse charge transfer or charge recombination even in the presence of sacrificial charge acceptors. Here, we show that cesium lead halide (CsPbX3) NCs can selectively photogenerate either aminium or aminyl radicals from amines, taking advantage of the controllable imbalance of the electron and hole populations achieved by varying the solvent composition. Using dihalomethane as the solvent, irreversible removal of the electrons from CsPbX3 NCs enabled by the photoinduced halide exchange between the NCs and the dihalomethane resulted in efficient oxidative generation of the aminium radical. In the absence of dihalomethane in solvent, the availability of both electrons and holes resulted in the production of an aminyl radical via sequential hole transfer and reductive N–H bond dissociation. The negative charge of the halide ions on the NC’s lattice surface appears to facilitate the aminyl radical production, competing favorably with the reversible charge transfer reverting to the reactant.

Ultrastable Anion Radicals in Ligand-Dimerized Frameworks for Self-Accumulated Electrochemiluminescence

“…To improve the stability of free radicals, − one common approach is to shield the radicals by introducing large substituents, − and another is to increase the delocalized nature of unpaired electrons on the molecular backbone. , Metal–organic frameworks (MOF) are a type of porous crystalline materials with strict skeleton and designable ligands . Introducing the conjugated ligands into MOFs can effectively improve the stability of radical intermediates owing to the rigid structure and shielding effect of frameworks. − For example, MOFs containing naphthalenediimides realized radical stabilization through the electron delocalization and spin-pairing of an in situ coplanar dimer structure within the framework .…”

Water-Mediated Photocatalytic Coproduction of Diesel Fuel Additives and Hydrogen from Dimethyl Ether

“…However, •OH is unselective and overoxidation of DME to CO 2 is thermodynamically favorable . Photogenerated holes can be selective, - but hole transfer from photocatalysts to C–H bonds is generally kinetically slow since C–H bonds have a high degree of covalency, and the orbits of C–H bonds and semiconductor surface are individually self-confined with a little overlap . Interfacial hole transfer to C–H bonds can be efficient for sulfides, such as CdS and ZnIn 2 S 4 , , which allows hole transfer to unactivated C–H bonds owing to direct hydrogen atom abstraction by generated surface sulfide radicals .…”