Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Institute for Molecular Science, Okazaki 444-8585, Japan.
Nat Chem. 2017 Oct;9(10):983-989. doi: 10.1038/nchem.2784. Epub 2017 May 29.
Singlet fission, in which a singlet exciton is converted to two triplet excitons, is a process that could be beneficial in photovoltaic applications. A full understanding of the dynamics of singlet fission in molecular systems requires detailed knowledge of the relevant potential energy surfaces and their (conical) intersections. However, obtaining such information is a nontrivial task, particularly for molecular aggregates. Here we investigate singlet fission in rubrene crystals using transient absorption spectroscopy and state-of-the-art quantum chemical calculations. We observe a coherent and ultrafast singlet-fission channel as well as the well-known and conventional thermally assisted incoherent channel. This coherent channel is accessible because the conical intersection for singlet fission on the excited-state potential energy surface is located very close to the equilibrium position of the ground-state potential energy surface and also because of the excitation of an intermolecular symmetry-breaking mode, which activates the electronic coupling necessary for singlet fission.
单线态裂变，即将单线态激子转化为两个三线态激子的过程，在光伏应用中可能是有益的。要全面了解分子体系中单线态裂变的动力学，需要详细了解相关的势能面及其（锥形）交点。然而，获得此类信息并非易事，尤其是对于分子聚集体而言。在这里，我们使用瞬态吸收光谱和最先进的量子化学计算研究了并五苯晶体中的单线态裂变。我们观察到一个相干且超快的单线态裂变通道，以及众所周知的传统热辅助非相干通道。这个相干通道是可及的，因为在激发态势能面上的单线态裂变的锥形交叉点非常接近基态势能面的平衡位置，而且还因为激发了一个分子间打破对称性的模式，这激活了单线态裂变所需的电子耦合。
