Microscopic theory of singlet exciton fission. II. Application to pentacene dimers and the role of superexchange
Microscopic theory of singlet exciton fission. II. Application to pentacene dimers and the role of superexchange
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DOI：
10.1063/1.4794427
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发表时间：
2013-03-21
影响因子：
4.4
通讯作者：
Reichman, David R.
中科院分区：
文献类型：
--
作者：
Berkelbach, Timothy C.;Hybertsen, Mark S.;Reichman, David R.
我们应用我们的理论形式单重态激子裂变，介绍了在以前的文件[T。C. Berkelbach，M. S. Hybertsen和D. R. Reichman，J.Chem.Phys.138，114102（2013）]到并五苯的分子二聚体，并五苯是一种广泛研究的材料，其在晶相中表现出单线态裂变。我们解决了一个长期存在的理论问题，即单重态裂变是否通过两个连续的电子转移步骤介导的电荷转移状态或通过直接的两个电子转移过程。我们发现了一个超交换介导的机制的证据，即裂变过程通过虚拟的电荷转移状态，这可能是非常高的能量进行。特别是，这种机制预测有效的单线态裂变的亚皮秒的时间尺度上，在合理的协议与实验。我们研究了分子振动在介导弛豫和退相干中所起的作用，发现不同的物理合理形式的浴弛豫函数给出了类似的结果。我们还研究了竞争的直接耦合机制，并发现它产生裂变速率较慢的超交换机制的二聚体相比。我们讨论了结晶并五苯的影响，包括二聚体模型的局限性。(C)2013年美国物理学会。[http：//dx.doi.org/10.1063/1.4794427]
We apply our theoretical formalism for singlet exciton fission, introduced in the previous paper [T. C. Berkelbach, M. S. Hybertsen, and D. R. Reichman, J. Chem. Phys. 138, 114102 (2013)] to molecular dimers of pentacene, a widely studied material that exhibits singlet fission in the crystal phase. We address a longstanding theoretical issue, namely whether singlet fission proceeds via two sequential electron transfer steps mediated by charge-transfer states or via a direct two-electron transfer process. We find evidence for a superexchange mediated mechanism, whereby the fission process proceeds through virtual charge-transfer states which may be very high in energy. In particular, this mechanism predicts efficient singlet fission on the sub-picosecond timescale, in reasonable agreement with experiment. We investigate the role played by molecular vibrations in mediating relaxation and decoherence, finding that different physically reasonable forms for the bath relaxation function give similar results. We also examine the competing direct coupling mechanism and find it to yield fission rates slower in comparison with the superexchange mechanism for the dimer. We discuss implications for crystalline pentacene, including the limitations of the dimer model. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794427]