Rozgonyi Tamás, Vankó György, Pápai Mátyás
Wigner Research Centre for Physics, P.O. Box 49, H-1525, Budapest, Hungary.
Commun Chem. 2023 Jan 9;6(1):7. doi: 10.1038/s42004-022-00796-z.
It has long been known that irradiation with visible light converts Fe(II) polypyridines from their low-spin (singlet) to high-spin (quintet) state, yet mechanistic interpretation of the photorelaxation remains controversial. Herein, we simulate the full singlet-triplet-quintet dynamics of the [Fe(terpy)] (terpy = 2,2':6',2"-terpyridine) complex in full dimension, in order to clarify the complex photodynamics. Importantly, we report a branching mechanism involving two sequential processes: a dominant MLCT→MC(T)→MC(T)→MC, and a minor MLCT→MC(T)→MC component. (MLCT = metal-to-ligand charge transfer, MC = metal-centered). While the direct MLCT→MC mechanism is considered as a relevant alternative, we show that it could only be operative, and thus lead to competing pathways, in the absence of MC states. The quintet state is populated on the sub-picosecond timescale involving non-exponential dynamics and coherent Fe-N breathing oscillations. The results are in agreement with the available time-resolved experimental data on Fe(II) polypyridines, and fully describe the photorelaxation dynamics.
长期以来，人们一直知道用可见光照射会使二价铁多吡啶配合物从低自旋（单重态）转变为高自旋（五重态），然而对光弛豫的机理解释仍存在争议。在此，我们全面模拟了[Fe(terpy)]（terpy = 2,2':6',2"-三联吡啶）配合物的完整单重态 - 三重态 - 五重态动力学，以阐明复杂的光动力学。重要的是，我们报告了一种涉及两个连续过程的分支机制：一个主要的MLCT→MC(T)→MC(T)→MC，以及一个次要的MLCT→MC(T)→MC组分。（MLCT = 金属到配体的电荷转移，MC = 以金属为中心）。虽然直接的MLCT→MC机制被认为是一种相关的替代机制，但我们表明，在没有MC态的情况下，它才可能起作用，从而导致竞争途径。五重态在亚皮秒时间尺度上形成，涉及非指数动力学和相干的Fe - N呼吸振荡。结果与关于二价铁多吡啶配合物的现有时间分辨实验数据一致，并完整地描述了光弛豫动力学。
