Photocatalytic Cascade Reaction Driven by Directed Charge Transfer over V-S-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 (O-1(2)) and proton-coupled electron transfer (PCET) over the photocatalyst Zn0.5Cd0.5S (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-center dot(2)-) and O-1(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 pi-pi 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.