Electron tunneling through interim ligand layers towards photoredox selective organic transformation

Abstract

Photocatalytic selective organic transformation represents an emerging avenue for artificial photosynthesis toward renewable solar energy conversion. However, solar-to-chemical conversion efficiency in photocatalysis is largely hampered by the sluggish charge transfer kinetic and difficulty in precise control over the charge migration pathway. Herein, we demonstrate conceptually new metal–insulator–semiconductor (MIS) electron tunneling photosystems to finely modulate the directional charge flow for photoredox selective organic transformation. The ultrathin insulating organic ligands layers capped on the surfaces of metal nanocrystals (NYs) and transition metal chalcogenides quantum dots (TMCs QDs) mutually function as precise directing-mediums to stimulate spontaneous electrostatic self-assembly between the tailor-made oppositely charged metal NYs and TMCs QDs for constructing metal (Au, Pd) NYs/TMCs (CdSe, CdS) QDs heterostructured electron tunneling photosystems. The electrons photoexcited from TMCs QDs can be efficaciously extracted and tunneled to metal NYs across the intermediate insulating hierarchical ligands layers to participate in the photoredox catalysis. The metal NYs-insulating ligands-TMCs QDs photosystems can efficiently mediate the minority carrier transport across the intermediate insulating ligand layers with minimal recombination, thereby resulting in the significantly enhanced net efficiency of multifarious photoactivities toward selective organic transformation including anaerobic photoreduction of nitroaromatics to amino derivatives and selective photo-oxidation of aromatic alcohols to aldehydes under visible light irradiation. The ligand-triggered electron tunneling effect has been evidence to be universal. Our work would inspire ongoing interest in exploring diverse organic ligands-based charge tunneling photosystems and provide a valuable roadmap for substantial solar energy conversion.