Mallik Sumitava, Wang Hailong, Matera Nunzio, Li Bi-Xiao, Stagni Stefano, Melchiorre Paolo
Department of Industrial Chemistry 'Toso Montanari', University of Bologna, via Piero Gobetti, 85 -, Bologna, 40129, Italy.
Angew Chem Int Ed Engl. 2025 Aug 25;64(35):e202509770. doi: 10.1002/anie.202509770. Epub 2025 Jul 9.
Bifunctional photocatalysts capable of mediating both single-electron transfer (SET) and energy transfer (EnT) processes are rare and typically metal based. Here, we present 3-thioaryl-4-hydroxycoumarins, a new family of cost-effective organic photocatalysts that leverage a stabilized charge-transfer (CT) excited state to achieve both strong reducing power and efficient energy transfer. The spatial separation of the HOMO and LUMO stabilizes the CT state, enhancing SET reactivity (E* = -3.08 V vs. SCE) while maintaining a sufficiently high triplet energy (E = 67 kcal mol) for EnT-driven transformations. This dual reactivity enables the activation of redox-inert substrates (E < -2.8 V vs. SCE) via SET reduction, generating radicals suitable for diverse C─S, C-─P, C─B, and C─C bond-forming transformations, alongside EnT-based processes such as E/Z olefin isomerization and [2 + 2] photocycloadditions. Mechanistic studies, supported by photophysical and theoretical analyses, confirmed the catalyst's bifunctionality.
能够介导单电子转移（SET）和能量转移（EnT）过程的双功能光催化剂非常罕见，且通常基于金属。在此，我们展示了3-硫芳基-4-羟基香豆素，这是一类新型的具有成本效益的有机光催化剂，它们利用稳定的电荷转移（CT）激发态来实现强大的还原能力和高效的能量转移。HOMO和LUMO的空间分离使CT态稳定，增强了SET反应活性（相对于饱和甘汞电极，E* = -3.08 V），同时保持足够高的三重态能量（E = 67 kcal/mol）以进行EnT驱动的转化。这种双重反应活性能够通过SET还原激活氧化还原惰性底物（相对于饱和甘汞电极，E < -2.8 V），生成适用于各种C─S、C─P、C─B和C─C键形成转化的自由基，以及基于EnT的过程，如E/Z烯烃异构化和[2 + 2]光环加成反应。光物理和理论分析支持的机理研究证实了该催化剂的双功能性。
