Proton-Coupled Electron Transfer in a Ruthenium(II) Bipyrimidine Complex in Its Ground and Excited Electronic States
Proton-Coupled Electron Transfer in a Ruthenium(II) Bipyrimidine Complex in Its Ground and Excited Electronic States
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处于基态和激发电子态的钌(II)联嘧啶络合物中的质子耦合电子转移
DOI：
10.1021/acs.jpca.2c02255
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Glusac, Ksenija D.
中科院分区：
文献类型：
--
作者：
Drummer, Matthew C.;Weerasooriya, Ravindra B.;Gupta, Nikita;Askins, Erik J.;Liu, Xiaolin;Valentine, Andrew J.;Li, Xiaosong;Glusac, Ksenija D.
研究了[Ru（terpy）（bpm）（OH 2）（PF 6）2]配合物Ru-bpm的基态和激发态的质子耦合电子转移（PCET）.循环伏安测试表明，Ru（II）-aqua在阳极区经PCET形成Ru（IV）-oxo，而bpm配体在阴极区经PCET形成bpmH 2.利用稳态和飞秒瞬态紫外-可见吸收光谱结合密度泛函理论（DFT）计算研究了Ru-bpm的光物理行为。Ru-bpm的最低激发态被描述为（Ru → bpm）金属-配体电荷转移（MLCT）态，而计算发现金属中心（MC）激发态的能量接近最低能量的明亮MLCT态（MC态比MLCT态高0.16 eV）。用瞬态吸收光谱法研究了Ru-bpm的激发态动力学，发现其激发态动力学寿命较短，符合双指数函数，寿命τ1= 4ps，τ2= 65 ps。两种衰变组分的动力学同位素效应分别为1.75（τ1）和1.61（τ2），表明溶剂在Ru-bpm的激发态动力学中起着重要作用。基于pH值依赖性的研究和以前的研究结果类似的钌络合物，我们假设，3 MLCT状态形成一个激发态氢键加合物的溶剂分子，这一过程发生在4 ps的寿命。这种氢键复合物的形成与3 MLCT状态下bpm部分的外围N原子处的电子密度累积一致。的氢键状态3 MLCT衰减到基态与65 ps的寿命。如此短的寿命可能与从3 MLCT态到溶剂的有效振动能量转移有关。
Proton-coupled electron transfer (PCET) was studied for the ground and excited electronic states of a [Ru(terpy)(bpm)(OH2)(PF6)2] complex,Ru-bpm. Cyclic voltammetry measurements show that the Ru(II)-aqua moiety undergoes PCET to form a Ru(IV)-oxo moiety in the anodic region, while the bpm ligand undergoes PCET to form bpmH2in the cathodic region. The photophysical behavior ofRu-bpmwas studied using steady-state and femtosecond transient UV–vis absorption spectroscopy, coupled with density functional theory (DFT) calculations. The lowest-lying excited state ofRu-bpmis described as a (Ru → bpm) metal-to-ligand charge-transfer (MLCT) state, while the metal-centered (MC) excited state was found computationally to be close in energy to the lowest-energy bright MLCT state (MC state was 0.16 eV above the MLCT state). The excited-state kinetics ofRu-bpmwere found via transient absorption spectroscopy to be short-lived and were fit well to a biexponential function with lifetimes τ1= 4 ps and τ2= 65 ps in aqueous solution. Kinetic isotope effects of 1.75 (τ1) and 1.61 (τ2) were observed for both decay components, indicating that the solvent plays an important role in the excited-state dynamics ofRu-bpm. Based on the pH-dependent studies and the results from prior studies of similar Ru-complexes, we hypothesize that the3MLCT state forms an excited-state hydrogen-bond adduct with the solvent molecules and that this process occurs with a 4 ps lifetime. The formation of such a hydrogen-bond complex is consistent with the electronic density accumulation at the peripheral N atoms of the bpm moiety in the3MLCT state. The hydrogen-bonded state3MLCT decays to the ground state with a 65 ps lifetime. Such a short lifetime is likely associated with the efficient vibrational energy transfer from the3MLCT state to the solvent.