Solvent Effect on the Photoinduced Structural Change of a Phosphorescent Molecular Butterfly
Solvent Effect on the Photoinduced Structural Change of a Phosphorescent Molecular Butterfly
复制标题
溶剂对磷光分子蝴蝶光致结构变化的影响
DOI：
10.1002/chem.201703259
复制
发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Ma, Biwu
中科院分区：
文献类型：
--
作者：
Ma, Ying-Zhong;Zhou, Chenkun;Doughty, Benjamin;Easley, Davis C.;Deterding, Justin;Ma, Biwu
光致结构变化（PSC）是基本的激发态动力学过程之一，但通常很难与具有相似或甚至相当时间尺度的竞争电子激发态弛豫通道区分开来。在这里，我们报告了一个吡唑桥联的铂（II）双核配合物，BFPtPZ（C^NPt（μ-pz′）2PtC^N，C^N=2-（2，4-二氟苯基）吡啶，pz′=吡唑），一个分子蝴蝶，在不同的波长和样品温度下，使用时间相关的单光子计数测量的PSC的详细研究。使用二氯甲烷（DCM）和碳酸亚乙酯（EC）作为溶剂获得的结果的分析使我们能够揭示对PSC方法的意外的强溶剂效应。我们发现，在DCM中观察到一个特征时间尺度为323 ps的快速PSC过程，这导致配体中心/金属-配体电荷转移（3LC/MLCT）和金属-金属-配体电荷转移（3 MMLCT）三重态之间的激发平衡。 随后从这些电子态到基态的弛豫发生在几纳秒内。相比之下，相应的PSC过程中EC出现缓慢，在我们的实验中研究的所有温度下，并没有表现出这样的激发平衡的迹象。发现所观察到的溶剂效应是由不同的溶剂性质引起的，包括它们的粘度和极性以及具有电荷转移特征的蝴蝶状分子的特殊电子激发态。
Photoinduced structural changes (PSC) is one of the fundamental excited‐state dynamic processes, and yet often very challenging to distinguish from competing electronic excited‐state relaxation channels having similar or even comparable timescales. Here, we report a detailed study on the PSC of a pyrazolate bridged platinum(II) binuclear complex, BFPtPZ (C^NPt(μ‐pz′)2PtC^N, C^N=2‐(2,4‐difluorophenyl)pyridine, pz′=pyrazolate), a molecular butterfly, using time‐correlated single photon counting measurements at different wavelengths and sample temperatures. Analysis of the results obtained using dichloromethane (DCM) and ethylene carbonate (EC) as solvents enabled us to reveal an unexpected, strong solvent effect on the PSC processes. We show that a rapid PSC process with a characteristic timescale of 323 ps is observed in DCM, which leads to an excitation equilibrium between the ligand center/metal‐to‐ligand charge transfer (3LC/MLCT) and metal‐metal‐to‐ligand charge transfer (3MMLCT) triplet states. The subsequent relaxation from these electronic states to the ground state takes place in several nanoseconds. In contrast, the corresponding PSC process in EC appears slow at all temperatures studied in our experiments and showed no sign of such excitation equilibrium. The observed solvent effect is found to arise from distinct solvent properties including their viscosities and polarities as well as the peculiar electronic excited‐states of the butterfly‐like molecules with charge transfer character.