Chesler Rafi, Khan Souratosh, Mazumdar Sumit
Department of Physics, University of Arizona, Tucson, Arizona 85721, United States.
School of Information, University of Arizona, Tucson, Arizona 85721, United States.
J Phys Chem A. 2020 Dec 10;124(49):10091-10099. doi: 10.1021/acs.jpca.0c07938. Epub 2020 Dec 1.
Experiments in several intramolecular singlet fission materials have indicated that the triplet-triplet spin biexciton has a much longer lifetime than believed until recently, opening up loss mechanisms that can annihilate the biexciton prior to its dissociation to free triplets. We have performed many-body calculations of excited state wave functions of hypothetical phenylene-linked anthracene molecules to better understand linker-dependent behavior of dimers of larger acenes being investigated as potential singlet fission candidates. The calculations reveal unanticipated features that we show carry over to the real covalently linked pentacene dimers. Dissociation of the correlated triplet-triplet spin biexciton and free triplet generation may be difficult in acene dimers where the formation of the triplet-triplet spin biexciton is truly ultrafast. Conversely, relatively slower biexciton formation may indicate smaller spin biexciton binding energy and greater yield of free triplets. Currently available experimental results appear to support this conclusion. Whether or not the two distinct behaviors are consequences of distinct mechanisms of triplet-triplet generation from the optical singlet is an interesting theoretical question.
对几种分子内单线态裂变材料进行的实验表明，三重态-三重态自旋双激子的寿命比直到最近人们所认为的要长得多，这开启了一些损耗机制，这些机制能够在双激子解离为自由三重态之前将其湮灭。我们对假设的亚苯基连接的蒽分子的激发态波函数进行了多体计算，以便更好地理解作为潜在单线态裂变候选物正在被研究的更大并苯二聚体的连接体依赖性行为。计算结果揭示了一些意想不到的特征，我们发现这些特征也适用于实际的共价连接的并五苯二聚体。在并苯二聚体中，如果三重态-三重态自旋双激子的形成确实非常快，那么相关的三重态-三重态自旋双激子的解离和自由三重态的产生可能会很困难。相反，相对较慢的双激子形成可能表明自旋双激子结合能较小，自由三重态的产率较高。目前可得的实验结果似乎支持这一结论。这两种不同的行为是否是由光学单重态产生三重态-三重态的不同机制所导致的，这是一个有趣的理论问题。
