The branching reaction of α-methyl-cis-stilbene (cis-mSB) into its trans-mSB and 4a,4b-dihydrophenanthrene (DHP) forms upon ππ^∗ excitation was examined theoretically by exploring the excited-state potential energy surface and using on-the-fly molecular dynamics simulations at the spin-flip time-dependent density functional theory (SF-TDDFT) level of theory. The branching ratio of trajectories was calculated as DHP:twist = 11:29, where twist denotes a mid-region between the cis-form and trans-form, indicating that the trans-mSB is a dominant product. The branching mechanism was analyzed by comparison with the corresponding theoretical studies on stilbene (SB) and 1,1′-dimethyl-stilbene (dmSB). The present computations elucidate the origin of variations in the branching ratio in the photoreactions of cis-SB, cis-mSB, and cis-dmSB. We also found that, because of loss of the slow component of the decay to the ground state, cis-mSB shows a faster decay rate to the ground state than cis-SB and cis-dmSB.

α甲基的支化反应的顺式-芪（顺-mSB）到其反式-mSB和图4a，4b二氢菲（DHP）时ππ形式^*激励电压由探索激发态势能面，并使用在理论上检查在自旋翻转时间相关的密度泛函理论（SF-TDDFT）的理论层面上进行动态分子动力学模拟。轨迹的分支比计算为DHP：twist  = 11:29，其中twist表示顺式和反式之间的中间区域，表明反式-mSB是主要产品。通过与二苯乙烯（SB）和1,1'-二甲基二苯乙烯（dmSB）的相应理论研究相比较，分析了支化机理。本计算阐明了顺式-SB，顺式-mSB和顺式-dmSB的光反应中支化比变化的起源。我们还发现，由于失去了衰减到基态的慢分量，所以顺式-mSB的基态衰减速率比顺式-SB和顺式-dmSB快。