Non-conjugated polymer ligand: stimulating charge transfer towards photocatalytic selective organic transformation

Abstract

Utilizing photocatalytic techniques to selectively or non-selectively oxidize organics to target products represents a promising and sustainable way to increase the supply of energy and chemical feedstocks, and solve environmental pollution. However, photoredox reactions inevitably suffer from rapid charge recombination, sluggish charge transfer kinetics, and scarcity of catalytically active sites. Herein, we conceptually demonstrate the construction of a spatially unidirectional charge transfer channel over metal@polymer/semiconductor heterostructured photosystems which are elaborately designed by a polymer ligand-triggered self-assembly strategy. To this end, monodisperse tailor-made non-conjugated insulating poly(diallyldimethylammonium chloride) (PDDA)-capped metal (M: Au, Pd, Pt) nanocrystals (NCs) are controllably and uniformly anchored on the transition metal chalcogenides (TMCs: CdS, Zn_0.5Cd_0.5S) via molecular interactions. We found that electrons photoexcited over TMCs can be unidirectionally migrated to the closely integrated metal@PDDA NCs via the ultra-thin PDDA interim layer capped on the metal NC surface, wherein the metal core acts as a Schottky-type electron-trapping reservoir and the PDDA ligand functions as an intermediate charge transport mediator to relay the directional electron transfer from TMC substrates to the metal core that serves as the ultimate electron trap, hence resulting in the considerably enhanced charge separation/migration. These charge transport characteristics endow the self-assembled M@PDDA/TMC heterostructures with substantially improved photoactivities toward selective oxidation of aromatic alcohols to aldehydes under visible light irradiation. Moreover, we ascertain that such a non-conjugated insulating polymer dominated cascade charge transfer pathway is universal. Our work would inspire new ideas to strategically mediate interfacial charge transport via an insulating polymer for solar-driven organic transformation.