Polyoxometalate-based donor–acceptor-type photocatalytic-active cluster: Exploring structure–activity relationships in oxidation of alkylbenzene C(sp ³ )–H bond via ligand design

The selective oxidation of inert C(sp³)-H bonds in alkylbenzene remains a critical challenge in synthetic chemistry, necessitating advanced catalytic systems for sustainable C-H functionalization. Herein, we present a quinolinium-functionalized Anderson-type polyoxometalate (TBA-6MQ-Al) that achieves 64.24% toluene conversion and 57.32% benzoic acid yield under mild visible light (40 W 420−430 nm blue LED), outperforming conventional POM-based photocatalysts. Systematic investigations reveal that methyl substitution on the quinolinium ligand enhances intersystem crossing efficiency, promoting triplet-state formation for efficient O₂ activation. Radical quenching and EPR spectroscopy confirm superoxide/hydroxyl radicals and photogenerated electrons as key reactive species, while DFT calculations elucidate the electronic structure-activity relationship. This work establishes a molecular engineering paradigm for optimizing POM redox properties, advancing sustainable C-H oxidation strategies with potential applications in green catalysis.