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Insights into the Photoinduced Isomerization Mechanisms of a N,C–Chelate Organoboron Compound: A Theoretical Study
Author(s) -
Zhu HongYang,
Li QuanSong
Publication year - 2020
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.202000049
Subject(s) - photoisomerization , isomerization , conical intersection , intersystem crossing , photochromism , chemistry , photochemistry , density functional theory , complete active space , molecular switch , computational chemistry , molecule , singlet state , atomic physics , excited state , catalysis , physics , organic chemistry , basis set
As the first discovered organoboron compound with photochromic property, B(ppy)Mes 2 (ppy=2‐phenylpyridine, Mes=mesityl) displays rich photochemistry that constitutes a solid foundation for wide applications in optoelectronic fields. In this work, we investigated the B(ppy)Mes 2 to borirane isomerization mechanisms in the three lowest electronic states (S 0 , S 1 , and T 1 ) based on the complete active space self‐consistent field (CASSCF) and its second‐order perturbation (CASPT2) methods combined with time‐dependent density functional theory (TD‐DFT) calculations. Our results show that the photoisomerization in the S 1 state is dominant, which is initiated by the cleavage of the B‐C ppy bond. After overcoming a barrier of 0.5 eV, the reaction pathway leads to a conical intersection between the S 1 and S 0 states (S 1 /S 0 ) x , from which the decay path may go back to the reactant B(ppy)Mes 2 via a closed‐shell intermediate (Int1‐S 0 ) or to the product borirane via a biradical intermediate (Int2‐S 0 ). Although triplet states are probably involved in the photoinduced process, the possibility of the photoisomerization in T 1 state is very small owing to the weakly allowed S 1 →T 1 intersystem crossing and the high energy barrier (0.77 eV). In addition, we found the photoisomerization is thermally reversible, which is consistent with the experimental observations.