Singlet-state electron transfer between a porphyrin and ubiquinone: A transient resonance Raman and quantum chemical study
Singlet-state electron transfer between a porphyrin and ubiquinone: A transient resonance Raman and quantum chemical study
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DOI：
10.1021/jp980168v
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发表时间：
1998-11-05
影响因子：
3.3
通讯作者：
Ondrias, M
中科院分区：
文献类型：
--
作者：
Buranda, T;Enlow, M;Ondrias, M
由激发的单线态卟啉供体和醌受体之间的双分子电子转移产生的自由基离子对的寿命如此短，以至于很少被观察到。在这里，我们报告了游离碱内消旋四（4-磺基苯基）卟啉（P）和2,3-二甲氧基-5-甲基-1,4-苯醌（泛醌，UQ（0））的非共价复合物的光动力学光谱研究结果。 P和UQ(0)形成弱基态络合物（K-a近似于1.0 x 10(3) M-1），其在局部卟啉pi-pi*激发态的光激发后通过CT中间体衰变。瞬态共振拉曼光谱（TRRS）用于识别和表征该过程中的单线态相关电子转移中间体。瞬态卟啉阳离子模式具有良好的特征并且符合之前的分配。虽然泛醌自由基阴离子的一些预期模式被卟啉振动掩盖，但在瞬态 RR 光谱中，主要的 C=C 和 C=O 模式清晰可辨。从头计算用于帮助指定 UQ(0) 的观察模式并计算 UQ(0)/UQ(0)(.-) 自由基阴离子对的“自交换”重组能（大约 0.60 eV）。这些结果在现代电子转移理论的背景下进行了讨论。
Radical ion pairs resulting from bimolecular electron transfer between excited singlet porphyrin donors and quinone accepters have such short lifetimes that they are rarely observed. Here we report the results of a spectroscopic investigation of the photodynamics of a noncovalent complex of a free base meso-tetrakis (4-sulfonatophenyl)porphine (P) and 2,3-dimethoxy-5-methyl-1,4-benzoquinone (ubiquinone, UQ(0)). P and UQ(0) form a weak ground-state complex (K-a approximate to 1.0 x 10(3) M-1), which decays via a CT intermediate after photoexcitation of a local porphyrin pi-pi* excited state. Transient resonance Raman spectroscopy (TRRS) was employed to identify and characterize singlet-correlated electron-transfer intermediates in this process. The transient porphyrin cation modes are well-characterized and conform to previous assignments. While some of the modes expected of the ubiquinone radical anion are obscured by the porphyrin vibrations, the predominantly C=C and C=O modes are clearly discernible in the transient RR spectra. Ab initio calculations were used to help assign the observed modes of the UQ(0) and calculate "self-exchange" reorganizational energy (approximate to 0.60 eV) for the UQ(0)/UQ(0)(.-) radical anion pair. These results are discussed in the context of modern theories of electron transfer.