Metal-free polymeric and molecular disorder/order semiconductor heterojunctions for the visible-light photocatalytic Minisci reaction

Abstract

The photocatalytic Minisci reaction (PMR) is of great significance for fine chemical synthesis and the sustainable methodology of functionalized heteroarenes. However, the activity and stability of photocatalysts, as well as the selectivity of functionalized products, are the challenges of the current PMR, limiting its suitability for industrial production. Here, we report that a perylene-3,4,9,10-tetracarboxylic dianhydride/carbon nitride metal-free catalyst (PTCDA/g-C₃N₄) with a strong interfacial effect and steric selectivity can promote high separation of photogenerated carriers and selectivity of functionalized products. In the PMR model reaction of 4-methylquinoline with tetrahydrofuran, the elaborately designed PTCDA/g-C₃N₄ interface not only enables ˙O²⁻ and ¹O₂ species formation by weakening carrier recombination, but also promotes the formation of functionalized products instead of ring-open by-products of tetrahydrofuran by absorbing visible light. Importantly, PTCDA/g-C₃N₄ photocatalytic model reaction conversion and selectivity were up to 95% and 98.9%, respectively, in the presence of atmospheric O₂ and blue LED irradiation. And, after PTCDA/g-C₃N₄ as reused four times, the activity of the model reaction showed no significant loss in its reactivity. Further electron paramagnetic resonance (EPR), kinetic isotope effect (KIE) and radical-trapping studies elucidated the reaction mechanism evolving active oxygen (O) radicals mediating the PMR to realize the C–H alkylation of heteroarenes. This investigation provides an innovative way to develop high-performance inorganic solid semiconductor photocatalysts for the PMR under visible light.