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首页> 外文期刊>Journal of photochemistry and photobiology, C. Photochemistry reviews >Recombination of radical ion pairs of triplet multiplicity
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Recombination of radical ion pairs of triplet multiplicity

机译：三重多重自由基离子对的重组

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Radical ion pairs generated by photo-induced electron transfer or formed upon encounter of independently generated radical ions may undergo back electron pairs of triplet multiplicity. Triplet recombination has been probed by luminescence time-resolved optical spectroscopy (in combination with magnetic field effects), CIDNP spectroscopy, and opto-acoustic calorimetry. The free energy of back electron transfer and the topologies of the potential surfaces of parent molecule, radical ion and the accessible triplet state or biradical play significant roles in this recombination. The free energy governs the rate of back electron transfer and determines whether this process is competitive. The topologies of the intermediates may influence the course of the overall reaction. The topologies of the potential energy surfaces of ground state, radical ion, and triplet related in three different ways. First, aromatic donors/acceptors typically undergo only minor geometry upon oxidation, reduction or excitation to the triplet state. Therefore, rearrangements are unlikely. Alternatively, the connectivities of some radical ions resemble those molecule, whereas the corresponding triplet states (biradicals) have structures of different connectivities. In these cases, back electron transfer will populate a triplet (biradical) with cleaved bonds ("dissociative" electron return) or one with newly formed bonds ("associative" electron return) resulting in structural reorganizations. Third, the radical ions of some strained ring compounds may rearrange to ring-opened structures of lower energy. Here, triplet states or biradicals with geometries related to the rearrangement radical ions may be populated. Finally, triplet radical ion pairs may form C-C, C-N, or C-O bonds between radical anion and cation (charge recombination), generating "bimolecular" states. Following intersystem crossing, the biradicals may fragment to regenerate the reagents, generate adducts by forming a second bond (cyclization) or transfer of an atom or group between the two functions. The different intra-pair reactions of triplet radical are illustrated with appropriate examples.
机译：由光致电子转移产生或在遇到独立产生的自由基离子时形成的自由基离子对可能会经历三重态多重性的反向电子对。三重态重组已通过发光时间分辨光谱法（结合磁场效应），CIDNP光谱法和光声量热法进行了探索。反向电子转移的自由能以及母体分子的潜在表面的拓扑结构，自由基离子和可及的三重态或双自由基在该重组中起重要作用。自由能控制反向电子传输的速率，并确定该过程是否具有竞争力。中间体的拓扑结构可能会影响整个反应的过程。基态，自由基离子和三重态的势能表面的拓扑以三种不同方式关联。首先，芳族供体/受体通常在氧化，还原或激发至三重态时仅经历较小的几何形状。因此，重新排列是不可能的。或者，某些自由基离子的连接性类似于那些分子，而相应的三重态（双自由基）具有不同连接性的结构。在这些情况下，反向电子转移将在三重态（双自由基）中带有裂开的键（“解离”电子返回）或在一个新形成的键中（“缔合”电子返回），从而导致结构重组。第三，某些应变环化合物的自由基离子可能会重排为较低能量的开环结构。在此，可以填充具有与重排自由基离子有关的几何形状的三重态或双自由基。最后，三重态自由基离子对可在自由基阴离子和阳离子之间形成C-C，C-N或C-O键（电荷重组），从而产生“双分子”状态。在系统间穿越后，双自由基可能会碎裂以再生试剂，通过形成第二键（环化）或在两个功能之间转移原子或基团而生成加合物。用适当的例子说明了三重态自由基的不同对内反应。

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