In an effort to explain the experimentally observed variation of the photocatalytic activity of tBu3P, nBu3P and (MeO)3P in the blue-light regime [Helmecke et al., Org. Lett. 21 (2019) 7823], we have explored the absorption characteristics of several phosphine– and phosphite–IC4F9 adducts by means of relativistic density functional theory and multireference configuration interaction methods. Based on the results of these computational and complementary experimental studies, we offer an explanation for the broad tailing of the absorption of tBu3P-IC4F9 and (MeO)3P-IC4F9 into the visible-light region. Larger coordinate displacements of the ground and excited singlet potential energy wells in nBu3P-IC4F9, in particular with regard to the P–I–C bending angle, reduce the Franck–Condon factors and thus the absorption probability compared to tBu3P-IC4F9. Spectroscopic and computational evaluation of conformationally flexible and locked phosphites suggests that the reactivity of (MeO)3P may be the result of oxygen lone-pair participation and concomitant broadening of absorption. The proposed mechanism for the phosphine-catalyzed homolytic C–I cleavage of perfluorobutane iodide involves S1 ← S0 absorption of the adduct followed by intersystem crossing to the photochemically active T1 state.

中文翻译：

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膦介导的全氟烷基碘的可见光诱导均裂

为了解释实验观察到的 tBu3P、nBu3P 和 (MeO)3P 在蓝光状态下的光催化活性变化 [Helmecke 等人，Org. 莱特。21 (2019) 7823]，我们通过相对论密度泛函理论和多参考构型相互作用方法探索了几种膦-和亚磷酸酯-IC4F9加合物的吸收特性。基于这些计算和补充实验研究的结果，我们对 tBu3P-IC4F9 和 (MeO)3P-IC4F9 吸收到可见光区域的广泛拖尾进行了解释。与 tBu3P-IC4F9 相比，nBu3P-IC4F9 中地面和激发单线态势能阱的较大坐标位移，特别是 P-I-C 弯曲角，降低了 Franck-Condon 因子，从而降低了吸收概率。构象灵活和锁定的亚磷酸酯的光谱和计算评估表明 (MeO)3P 的反应性可能是氧孤对参与和伴随的吸收加宽的结果。膦催化的全氟丁烷碘化物的均裂 C-I 裂解的拟议机制涉及加合物的 S1 ← S0 吸收，然后系统间穿过光化学活性 T1 状态。