Zhou Zhongjun, Zhang Jilong, Qu Zexing
Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130023, China.
J Phys Chem A. 2022 Jul 14;126(27):4424-4431. doi: 10.1021/acs.jpca.2c02930. Epub 2022 Jun 28.
The detailed mechanism of photoinduced dearomatization of benzenoid arenes is investigated using both the high-level method and density functional theory. The results suggest that the optically allowed singlet excited state (S) can quickly decay to the lowest triplet excited state (T) through a barrierless internal conversion and intersystem crossing. Importantly, we find a triplet excited state intramolecular proton transfer (T-ESIPT) pathway to produce a diradical triplet intermediate (M), which can trigger the subsequent [4 + 2] dearomatization reaction. Furthermore, the diastereoselectivity of the reaction was illustrated by the rotation of the OH group of M, which could be effectively modulated by the solvent effect (arising from the strength of the intermolecular hydrogen bond) and the substituted effect (arising from the strength of the electron-donation group). This photochemical mechanism can explain well the experimental observations, and the novel T-ESIPT process can open a new door in studying the photoinduced proton transfer reactions.
采用高水平方法和密度泛函理论研究了苯型芳烃光致脱芳构化的详细机理。结果表明，光学允许的单重激发态（S）可通过无势垒的内转换和系间窜越迅速衰减至最低三重激发态（T）。重要的是，我们发现了一条三重激发态分子内质子转移（T-ESIPT）途径，以产生双自由基三重态中间体（M），其可引发随后的[4 + 2]脱芳构化反应。此外，通过M的OH基团的旋转说明了反应的非对映选择性，其可通过溶剂效应（由分子间氢键的强度引起）和取代效应（由给电子基团的强度引起）进行有效调节。这种光化学机理能够很好地解释实验现象，并且新型的T-ESIPT过程可为研究光致质子转移反应打开一扇新的大门。
