Xu Xinyue, Marlton Samuel J P, Flint Kate L, Hudson Rohan J, Keene F Richard, Hall Christopher R, Smith Trevor A
School of Chemistry, The University of Melbourne, Parkville, Victoria 3010, Australia.
ARC Centre of Excellence in Exciton Science, Parkville, Victoria 3010, Australia.
J Phys Chem A. 2024 May 9;128(18):3587-3595. doi: 10.1021/acs.jpca.4c01996. Epub 2024 Apr 19.
The metal-ligand charge transfer (MLCT) and phosphorescence-quenching metal-centered (MC) states of the helicate and mesocate diastereoisomers of a double-stranded dinuclear polypyridylruthenium(II) complex have been investigated using ultrafast transient absorption spectroscopy. At 294 K, transient signals of the helicate decayed significantly slower than those of the mesocate, whereas at 77 K, no clear contrast in kinetics was observed. Contributions to excited-state decay from high-lying MLCT states were identified at both temperatures. Spectroscopic data (294 K) suggest that the MC state of the helicate lies above the MLCT and that the reverse is true for the mesocate; this was further validated by density functional theory calculations. The stabilization of the MC state relative to the MLCT state in the mesocate was explained by a reduction in ligand field strength due to distortion near the ligand bridge, which causes further deviation from octahedral geometry compared to the helicate. This work illustrates how minor structural differences can significantly influence excited state dynamics.
利用超快瞬态吸收光谱研究了双链双核聚吡啶钌（II）配合物的螺旋异构体和中位异构体的金属-配体电荷转移（MLCT）和磷光猝灭金属中心（MC）态。在294 K时，螺旋异构体的瞬态信号衰减明显慢于中位异构体，而在77 K时，未观察到动力学上的明显差异。在两个温度下都确定了高位MLCT态对激发态衰减的贡献。光谱数据（294 K）表明，螺旋异构体的MC态高于MLCT态，而中位异构体则相反；密度泛函理论计算进一步证实了这一点。中位异构体中MC态相对于MLCT态的稳定是由于配体桥附近的畸变导致配体场强度降低，与螺旋异构体相比，这导致与八面体几何形状的进一步偏离。这项工作说明了微小的结构差异如何能显著影响激发态动力学。
