Excited-State Processes of Cyclometalated Platinum(II) Charge-Transfer Dimers Bridged by Hydroxypyridines
Excited-State Processes of Cyclometalated Platinum(II) Charge-Transfer Dimers Bridged by Hydroxypyridines
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DOI：
10.1021/acs.inorgchem.7b02736
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发表时间：
2018-02-05
影响因子：
4.6
通讯作者：
Castellano, Felix N.
中科院分区：
文献类型：
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作者：
Chakraborty, Arnab;Yarnell, James E.;Castellano, Felix N.
提出了一系列具有金属-金属-配体电荷转移（MMLCT）激发态的四种反定位双核铂（II）配合物，它们由2-羟基-6-甲基吡啶或2-羟基-6-苯基吡啶桥接，并与7,8-苯喹啉或2-苯基吡啶环金属化。2-羟基吡啶桥接配体控制分子内d(8)-d(8)金属之间的sigma相互作用，影响前沿轨道的电子结构，导致这些配合物的基态和激发态性质发生显著变化。在循环伏安实验中，由于分子内的亲金属相互作用，其中三种分子具有可逆的单电子氧化。在这一系列分子中，x射线晶体学显示Pt-Pt距离在2.815至2.878埃之间；前者代表了具有低能MMLCT跃迁的铂（II）二聚体所报道的最短金属距离。本文报道的所有四种分子都显示出500 nm以上的可见吸收带，并且在室温下具有基于mmlct的700 nm以上的红色光致发光（PL），具有高PL量子产率（高达4%）和长激发态寿命（高达341 ns）。后者记录使用瞬态PL和瞬态吸收实验，自一致地产生定量相同的激发态寿命。能隙定律成功地应用于这一系列发色团，首次在具有MMLCT激发态的分子中记录了这种行为。综合数据表明，可以设想使用桥接吡啶氢氧化物与各种CN胞金属酸盐合作，以实现适合激发态电子和能量转移化学的光物理性质，从而形成全新类型的MMLCT发色团。
A series of four anti-disposed dinuclear platinum(II) complexes featuring metal-metal-to-ligand charge-transfer (MMLCT) excited states, bridged by either 2-hydroxy-6-methylpyridine or 2-hydroxy-6-phenylpyridine and cyclometalated with 7,8-benzoquinoline or 2-phenylpyridine, are presented. The 2-hydroxypyridine bridging ligands control intramolecular d(8)-d(8) metal metal sigma interactions, affecting the frontier orbitals' electronic structure, resulting in marked changes to the ground- and excited-state properties of these complexes. Three of these molecules possess reversible one electron oxidations in cyclic voltammetry experiments as a result of strong intramolecular metallophilic interactions. In this series of molecules, X-ray crystallography revealed Pt-Pt distances ranging between 2.815 and 2.878 angstrom; the former represents the shortest reported metal metal distance for platinum(II) dimers possessing low-energy MMLCT transitions. All four molecules reported here display visible absorption bands beyond 500 nm and feature MMLCT-based red photoluminescence (PL) above 700 nm at room temperature with high PL quantum yields (up to 4%) and long excited-state lifetimes (up to 341 ns). The latter were recorded using both transient PL and transient absorption experiments that self-consistently yielded quantitatively identical excited-state lifetimes. The energy-gap law was successfully applied to this series of chromophores, documenting this behavior for the first time in molecules possessing MMLCT excited states. The combined data illustrate that entirely new classes of MMLCT chromophores can be envisioned using bridging pyridyl hydroxides in cooperation with various CN cydometalates to achieve photophysical properties suitable for excited-state electron- and energy-transfer chemistry.