Theoretical investigation of the reaction mechanism of the photoisomerization of 1,2-dihydro-1,2-azaborine

Abstract The photoisomerization of 1,2-dihydro-1,2-azaborine was investigated by high-level multireference ab initio and density functional theory calculations. The intermediates (IMs) and transition states (TSs) on the S₀ and S₁ states were optimized using the state-averaged complete active space self-consistent field method. The multireference configuration interaction method with the Davidson correction was used to obtain accurate energetics. Moreover, the conical intersections (CIs), which play a crucial role in photoisomerization, were also optimized. On the basis of the calculation results, the most favorable proposed reaction pathway is as follows: reactant→Franck-Condon region→TS₁→CI→IM₀→TS_0P→product. The product was not directly formed through the CI, and the IM₀ existed on the S₀ state. These results show that the isomerization of 1,2-dihydro-1,2-azaborine involves both photoreactions and thermal reactions. The calculated results clarify recent experimental observations. On a higher level: The isomerization reaction of 1,2-dihydro-1,2-azaborine is investigated by high-level multireference ab initio and density functional theory calculations. The mechanism involves both thermal reactions and photoreactions. The calculated results clarify recent experimental observations of a complete conversion of 1,2-dihydro-1,2-azaborine (R) into the BN-Dewar isomer (P) by UV irradiation.