The Fe(II) low-spin (LS; ¹A_1g, t_2g⁶e_g⁰) → high-spin (HS; ⁵T_2g, t_2g⁴e_g²) light-induced excited spin state trapping (LIESST) mechanism solely involving metal-centered states is revealed by synergistic spin-vibronic dynamics simulations. For the octahedral [Fe(NCH)₆]²⁺ complex, we identify an initial ∼100 fs ¹T_1g → ³T_2g intersystem crossing, controlled by vibronic coupling to antisymmetric Fe–N stretching motion. Subsequently, population branching into ³T_1g, ⁵T_2g (HS), and ¹A_1g (LS) is observed on a subpicosecond time scale, with the dynamics dominated by coherent Fe–N breathing wavepackets. These findings are consistent with ultrafast experiments, methodologically establish a new state of the art, and will give a strong impetus for further intriguing dynamical studies on LS → HS photoswitching.

中文翻译：

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协同自旋-振动动力学揭示了八面体 Fe(II) 配合物的光致低自旋 → 高自旋机制

Fe(II) 低自旋 (LS; ¹ A _1g , t _2g ⁶ e _g ⁰ ) → 高自旋 (HS; ⁵ T _2g , t _2g ⁴ e _g ² ) 光诱导激发自旋态俘获 (LIESST)协同自旋振动动力学模拟揭示了仅涉及金属中心状态的机制。对于八面体 [Fe(NCH) ₆ ] ^{2+ 配合}物，我们确定了初始的 ∼100 fs ¹ T _1g → ³ T _2g系统间交叉，由与反对称 Fe-N 拉伸运动的振动耦合控制。随后，在亚皮秒时间尺度上观察到分支为³ T _1g、⁵ T _2g (HS) 和¹ A _1g (LS) 的种群，其动力学由相干 Fe-N 呼吸波包主导。这些发现与超快实验一致，在方法上建立了一种新的技术水平，并将为进一步有趣的 LS → HS 光开关动力学研究提供强大动力。