Near-Infrared-Driven C–H Functionalization via Synergistic Energy Transfer Upconversion and Interfacial Quantum Dots

Near-infrared (NIR) energy transfer upconversion (ETU) overcomes the photon energy limitations of single-photon processes via nonlinear optical effects, demonstrating unique advantages in deep material penetration and multielectron transfer. This work reports a high-efficiency photocatalytic system that synergizes NIR-driven ETU with Co₃O₄ quantum dots (QDs). By integrating Er³⁺-doped upconversion nanoparticles (NaYF₄,Yb:Er) with Co₃O₄ QD-modified g-C₃N₄ nanosheets, we achieved energy conversion dominated by the ETU process under 980 nm NIR irradiation. Experimental power-dependent emission slopes of 2.23 (541 nm) and 1.89 (657 nm) confirm the underlying ETU mechanism, a typical two-photon-participating process. Yb³⁺ sensitizers absorb NIR photons, transfer energy to Er³⁺ for 4f-level transitions, and relay excited-state energy to the Co₃O₄/g-C₃N₄ nanosheets heterojunction via Förster resonance energy transfer (FRET). The Co₃O₄ QDs act as electron traps to enhance charge separation while activating O₂ to generate superoxide radicals (O₂^-) and enabling hole-mediated oxidation, establishing a radical chain reaction pathway initiated by the ETU process. This system achieves challenging transformations under NIR, including benzyl C-H oxidation and thioether-specific conversions, successfully constructing omeprazole derivatives and 5<i>H</i>-benzo[<i>e</i>][1,4]-diazepine scaffolds. Compared to visible-light catalysts, it exhibits superior recyclability (>7 cycles), gram-scale capacity, and broad spectral response (200-1000 nm), offering a solar-driven strategy for green pharmaceutical synthesis. By decoupling photocatalysis from visible-light dependence through synergistic quantum dot interface engineering and an ETU-based strategy, this work advances NIR energy utilization in organic synthesis.