Computational investigation on the low‐lying photo‐excited states of N‐tert‐butyl‐α‐phenylnitrone (PBN), a well‐known spin‐trap agent, has revealed its photo‐product (oxaziridine) formation channel. The S0‐S2 vertical excitation in PBN is subsequently followed by a non‐radiative decay pathway through S2/S1 and S0/S1 conical intersections (CIs) with CNO‐kinked structures, situated around 23 kcal/mol and 45 kcal/mol below the vertically excited S2 state, respectively. The reverse photo‐process of PBN formation involves photo‐excitation of oxaziridine to its S2 and S3 photo‐excited states. The forward photo‐isomerization leads to the trans‐oxaziridine with a backside CNO kink (trans‐OXB) while the reverse path studied by us, connects its front‐side CNO‐kinked analogue (trans‐OXF) with the PBN. Our search for the reverse thermal reaction paths from these two oxazirdines has led to their corresponding transition states, one at 35 kcal/mol and the other at 27 kcal/mol above trans‐OXF and trans‐OXB geometries, respectively. They lead to two different isomers (E and Z) of PBN which supports the reported nature of products from the trans‐oxaziridine in this thermal reaction. The inversion path of the chiral nitrogen atom of this N‐tert‐butyl‐oxaziridine (barrier 21 kcal/mol) has also been tracked. This reaction path has been compared with that of the N‐methyl (barrier 30 kcal/mol) and N‐acyl (barrier 10.5 kcal/mol) oxaziridine analogues.

中文翻译：

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流行的自旋捕获剂 N-叔丁基-α-苯基硝酮 (PBN) 的光化学及其光产物氧氮丙啶的热异构化途径的计算研究

低位光激发态的计算研究氮著名的自旋捕获剂-叔丁基-α-苯基硝酮（PBN）揭示了其光产物（氧氮丙啶）的形成通道。 S0‐S2PBN 中的垂直激发随后是通过 S 的非辐射衰变路径2/S1和S0/S1具有 CNO 扭结结构的圆锥形交叉点 (CI)，位于垂直激发 S 下方约 23 kcal/mol 和 45 kcal/mol2状态，分别。 PBN 形成的逆光过程涉及氧氮丙啶对其 S 的光激发2和S3光激发态。正向光致异构化导致反式‐具有背面 CNO 扭结的氧氮丙啶（反式-牛乙）而我们研究的反向路径则连接其前端 CNO 扭结类似物（反式-牛F）与PBN。我们对这两种恶嗪啶的逆热反应路径的研究导致了它们相应的过渡态，一种在 35 kcal/mol，另一种在 27 kcal/mol 以上。反式-牛F和反式-牛乙分别是几何形状。它们产生两种不同的异构体（乙和Z）的PBN，支持所报告的产品性质反式‐氧杂氮丙啶在此热反应中。该化合物手性氮原子的反转路径氮‐叔丁基氧氮丙啶（屏障 21 kcal/mol）也已被追踪。该反应路径与氮‐甲基（屏障 30 kcal/mol）和氮‐酰基（屏障 10.5 kcal/mol）氧氮丙啶类似物。