Photocatalytic redox reactions are important for synthesizing fine chemicals from olefins, but the limited lifetime of radical cation intermediates severely restricts semiconductor photocatalysis efficiency. Here, we report that Ag₃PO₄ can efficiently catalyze intramolecular and intermolecular [2 + 2] and Diels-Alder cycloadditions under visible-light irradiation. The approach is additive-free, catalyst-recyclable. Mechanistic studies indicate that visible-light irradiation on Ag₃PO₄ generates holes with high oxidation power, which oxidize aromatic alkene adsorbates into radical cations. In photoreduced Ag₃PO₄, the conduction band electron (e_CB⁻) has low reduction power due to the delocalization among the Ag⁺-lattices, while the particle surfaces have a strong electrostatic interaction with the radical cations, which considerably stabilize the radical cations against recombination with e_CB⁻. The radical cation on the particle’s surfaces has a lifetime of more than 2 ms, 75 times longer than homogeneous systems. Our findings highlight the effectiveness of inorganic semiconductors for challenging radical cation-mediated synthesis driven by sunlight.

光催化氧化还原反应对于从烯烃合成精细化学品非常重要，但自由基阳离子中间体的有限寿命严重限制了半导体光催化效率。在这里，我们报道Ag ₃ PO ₄在可见光照射下可以有效地催化分子内和分子间[2 + 2]和Diels-Alder环加成反应。该方法无添加剂，催化剂可回收。机理研究表明，可见光照射Ag ₃ PO ₄会产生具有高氧化能力的空穴，将芳香族烯烃吸附物氧化成自由基阳离子。在光还原Ag ₃ PO ₄中，由于Ag ⁺晶格之间的离域，导带电子（ e _CB ^- ）具有较低的还原能力，而颗粒表面与自由基阳离子有很强的静电相互作用，这大大稳定了自由基阳离子防止与e _CB ⁻重组。颗粒表面的自由基阳离子的寿命超过 2 毫秒，是均质系统的 75 倍。我们的研究结果强调了无机半导体对于挑战由阳光驱动的自由基阳离子介导的合成的有效性。