Theoretical Study on Photoisomerization Mechanisms of Diphenyl-Substituted N,C-Chelate Organoboron Compounds

N,C-chelate organoboron compounds are widely employed as photoresponsive and optoelectronic materials due to their efficient photochromic reactivity. It was found in experiments that two diphenyl-substituted organoboron compounds, namely B(ppy)Ph-2(ppy=2-phenylpyridyl) and B(iba)Ph-2(iba=N-isopropylbenzylideneamine), show distinct photochemical reactivity. B(ppy)Ph(2)is inert on irradiation, whereas B(iba)Ph(2)undergoes photoinduced transformations, yielding BN-cyclohepta-1,3,5-triene via a borirane intermediate. In this work, the complete active space self-consistent field and its second-order perturbation (CASPT2//CASSCF) methods were used to investigate the photoinduced reaction mechanisms of B(ppy)Ph(2)and B(iba)Ph-2. The calculations showed that the two compounds isomerize to borirane in the same way by passing a transition state in the S(1)state and a conical intersection between the S(1)and S(0)states. The energy barriers in the S(1)state of 0.54 and 0.26 eV for B(ppy)Ph(2)and B(iba)Ph-2, respectively, were explained by analyzing the charge distributions of minima in S(0)and S(1)states. The results provide helpful insights into the excited-state dynamics of organoboron compounds, which could assist in rational design of boron-based photoresponsive materials.