Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
J Chem Phys. 2018 Jun 28;148(24):244701. doi: 10.1063/1.5031778.
We extend the vibronic exciton theory introduced in our previous work to study singlet fission dynamics, in particular addressing recent indications of the importance of vibronic coupling in this process. A microscopic and non-perturbative treatment of electronic and selected vibrational degrees of freedom in combination with Redfield theory allows us to dynamically consider clusters of molecules under conditions close to those in molecular crystals that exhibit fission. Using bulk pentacene as a concrete example, our results identify a number of factors that render fission rapid and effective. Strong coupling to high-frequency Holstein modes generates resonances between the photo-prepared singlet and product triplet states. We furthermore find the large number of triplet combinations associated with bulk periodic systems to be critical to the fission process under such vibronically resonant conditions. In addition, we present results including, in an approximate manner, the effects of Peierls coupling, indicating that this factor can both enhance and suppress fission depending on its interplay with vibronic resonance and thermodynamics.
我们将在之前的工作中引入的协同激子理论扩展到研究单重态裂变动力学，特别是针对最近表明协同作用在这个过程中的重要性的一些迹象。电子和选定的振动自由度的微观和非微扰处理与 Redfield 理论相结合，使我们能够在接近表现出裂变的分子晶体的条件下动态地考虑分子簇。使用体相五苯作为具体示例，我们的结果确定了一些因素，这些因素使得裂变快速而有效。与高频 Holstein 模式的强耦合在光制备的单重态和产物三重态之间产生共振。我们还发现，与体相周期性系统相关的大量三重态组合对于在这种协同共振条件下的裂变过程至关重要。此外，我们给出了包括以近似方式考虑 Peierls 耦合的结果，表明该因素可以根据其与协同共振和热力学的相互作用来增强或抑制裂变。
