Low-Toxicity ZnSe/ZnS Quantum Dots as Potent Photoreductants and Triplet Sensitizers for Organic Transformations.

Abstract

Colloidal quantum dots (QDs) can photocatalyze diverse organic reactions. However, reported QD-photocatalysts often contain highly-toxic elements Cd or Pb, and have not surpassed prototypical transition-metal complexes in terms of their photoredox power or excited-state energy. Here we report low-toxicity ZnSe/ZnS core/shell QDs as potent visible photocatalysts to drive challenging organic transformations. To overcome the limitation of short excited-state lifetime of the QDs, we functionalize their surfaces with benzophenone ligands which can rapidly extract electrons from photoexcited QDs and sustain long-lived charge-separated states. The benzophenone anions function as potent electron relay to drive dehalogenation of aryl chlorides and additive-free polymerization of acrylates. Alternatively, the QDs are functionalized with biphenyl ligands to store energy in long-lived, energetic triplets, enabling [2+2] homo-cycloaddition of styrene and cycloaddition of carbonyls with alkenes.