Ultrafast non-adiabatic dynamics of the small heteroaromatic compound 2-thiopyridone has been studied with surface hopping simulations based on multi-configurational quantum chemistry. Initial excitation of the bright ${\text{S}}_2(\pi ,{\pi }^{*})$ state is found to promptly relax to ${\text{S}}_1(n,\hspace{0.17em}{\pi }^{*}$) through in-plane motion. The subsequent dynamics are oppositely driven by out-of-plane motion, which results in both complex population transfers among all the available states and intersystem crossing predominantly through the “El-Sayed forbidden” ${\text{S}}_1(n,\hspace{0.17em}{\pi }^{*}$) to ${\text{T}}_2(n,\hspace{0.17em}{\pi }^{*}$) channel, through significant mixing of electronic excitation characters. Despite this complexity, the femto- to picosecond triplet population, expected from several spectroscopic measurements, is well described as a simple exponential decay of the singlet state manifold. No proton transfer is found in the reported trajectories, but two mechanisms for its possible mediation in previously reported experiments are proposed based on the observed structural dynamics: (i) ultrafast intra-molecular transfer driven by the initially coherent in-plane motion and (ii) inter-molecular solvent-mediated transfer driven by the out-of-plane modes that dominate the later motion.

中文翻译：

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光激发的2-硫代吡啶酮的超快动力学：三重态态人口和质子转移途径的理论见解

通过基于多构型量子化学的表面跳跃模拟研究了小的杂芳族化合物2-硫代吡啶酮的超快非绝热动力学。初始激发光${\text{小号}}_2（\pi ，{\pi }^{*}）$ 发现状态可以立即放松到 ${\text{小号}}_{\mathrm{1个}}（ñ，\hspace{0.17em}{\pi }^{*}$）通过平面运动。后续动力由平面外运动相反地驱动，这导致所有可用状态之间的复杂种群转移以及主要通过“ El-Sayed禁止”的系统间交叉${\text{小号}}_{\mathrm{1个}}（ñ，\hspace{0.17em}{\pi }^{*}$） 至 ${\text{Ť}}_2（ñ，\hspace{0.17em}{\pi }^{*}$）通道，通过大量混合电子激发特性。尽管存在这种复杂性，但是通过数个光谱测量结果预期的飞秒级至皮秒级三重态种群被很好地描述为单重态流形的简单指数衰减。在所报告的轨迹中未发现质子转移，但是基于观察到的结构动力学，在先前报告的实验中提出了两种可能的介导机制：（i）由最初相干的平面内运动驱动的超快分子内转移和（ii） ）由面外模式驱动的分子间溶剂介导的转移，而后者主导了以后的运动。