Dearomatization of Benzenoid Arenes Triggered by Triplet Excited State Intramolecular Proton Transfer

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 (S 2 ) can quickly decay to the lowest triplet excited state (T 1 ) 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 ( 3 M O−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 3 M O−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.

Characterizing the excited states of large photoactive systems by exciton models

“…Characterizing the excited states of large photoactive systems is crucial for understanding various important photophysical or photochemical processes in the condensed phases, ranging from optoelectronic conversion in material science to light harvesting in biological photosynthetic system. [1][2][3][4][5][6][7][8][9] However, the computational capability is usually limited to small molecular systems (approximately 150-200 atoms) [10] with traditional ab initio excited state quantum chemistry methods, such as configuration interaction singles (CIS) and timedependent density function theory (TDDFT). To handle larger photoactive systems in condensed phase, various low-scaling excited state approaches based on local excitation approximation (LEA) [11][12][13][14][15] or local correlation approximation (LCA) [16][17][18][19] have been proposed in recent years.…”