Photocatalytic Cascade Reaction Driven by Directed Charge Transfer over VS-Zn0.5Cd0.5S/GO for Controllable Benzyl Oxidation

Photocatalysis is an important technique for synthetic transformations. However, little attention has been paid to light-driven synergistic redox reactions for directed synthesis. Herein, the authors report tunable oxidation of benzyl to phenylcarbinol with the modest yield (47%) in 5 h via singlet oxygen ( 1 O 2 ) and proton-coupled electron transfer (PCET) over the photocatalyst Zn 0.5 Cd 0.5 S (ZCS)/graphene oxide (GO) under exceptionally mild conditions. Theoretical calculations indicate that the presence of S vacancies on the surface of ZCS/GO photocatalyst is crucial for the adsorption and activation of O 2 , successively generating the superoxide radical ( • O 2 − ) and 1 O 2 , attributing to the regulation of local electron density on the surface of ZCS/GO and photogenerated holes (h + ). Meanwhile, accelerated transfer of photogenerated electrons (e − ) to GO caused by the π – π stacking effect is conducive to the subsequent aldehyde hydrogenation to benzyl alcohol rather than non-selective oxidation of aldehyde to carboxylic acid. Anisotropic charge transport driven by the built-in electric field can further promote the separation of e − and h + for multistep reactions. Promisingly, one-pot photocatalytic conversion of p -xylene to 4-methylbenzyl alcohol is beneficial for reducing the harmful effects of aromatics on human health. Furthermore, this study provides novel insights into the design of photocatalysts for cascade reactions.