Reverse intersystem crossing (RISC) has become possible by minimizing the energy gap between the first excited singlet (S₁) and triplet state (T₁), which facilitates the thermally activated delayed fluorescence (TADF). Due to the small singlet–triplet energy gap, the S₁ and T₁ states exhibit comparable redox reactivity, leading organic TADF compounds to be potent photocatalysts. Here, we report such TADF compounds with multiple donor units designed as an efficient photocatalyst for the direct C(sp³)-H carbamoylation of saturated aza-heterocycles. The results obtained by photophysical investigations and chemical calculations confirm that both the S₁ and T₁ states are involved in the photocatalysis cycle, with the fast spin-flip from the S₁ to triplet states being a crucial factor in the enhancement of catalytic performance. The findings will be beneficial for the design of novel, efficient organic photocatalysis with TADF characteristics and aid in the development of organic photocatalysis.

中文翻译：

---

有机热活化延迟荧光化合物的光催化机制


通过最小化第一激发单重态 （S₁） 和三重态 （T₁） 之间的能隙，反向系统间交叉 （RISC） 已成为可能，这促进了热激活延迟荧光 （TADF）。由于单重态-三重态能隙小，S₁ 和 T₁ 态表现出相当的氧化还原反应性，导致有机 TADF 化合物成为有效的光催化剂。在这里，我们报道了具有多个供体单元的 TADF 化合物，这些化合物被设计为用于饱和氮杂环的直接 C（sp³）-H 氨基甲酰化的有效光催化剂。通过光物理研究和化学计算获得的结果证实，S₁ 和 T₁ 态都参与了光催化循环，从 S₁ 到三重态的快速自旋翻转是增强催化性能的关键因素。这些发现将有助于设计具有 TADF 特性的新型、高效的有机光催化，并有助于有机光催化的发展。