Zhou Z, Zhang J, Qu Z. Dearomatization of Benzenoid Arenes Triggered by Triplet Excited State Intramolecular Proton Transfer.
J Phys Chem A 2022;
126:4424-4431. [PMID:
35763759 DOI:
10.1021/acs.jpca.2c02930]
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Abstract
The detailed mechanism of photoinduced dearomatization of benzenoid arenes is investigated using both the high-level ab initio method and density functional theory. The results suggest that the optically allowed singlet excited state (S2) can quickly decay to the lowest triplet excited state (T1) 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 (3MO-H), which can trigger the subsequent [4 + 2] dearomatization reaction. Furthermore, the diastereoselectivity of the reaction was illustrated by the rotation of the O-H group of 3MO-H, 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.
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