Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
J Chem Phys. 2017 May 7;146(17):174703. doi: 10.1063/1.4982362.
Recent time-resolved spectroscopic experiments have indicated that vibronic coupling plays a vital role in facilitating the process of singlet fission. In this work, which forms the first article of a series, we set out to unravel the mechanisms underlying singlet fission through a vibronic exciton theory. We formulate a model in which both electronic and vibrational degrees of freedom are treated microscopically and non-perturbatively. Using pentacene as a prototypical material for singlet fission, we subject our theory to comparison with measurements on polarization-resolved absorption of single crystals, and employ our model to characterize the excited states underlying the absorption band. Special attention is given to the convergence of photophysical observables with respect to the basis size employed, through which we determine the optimal basis for more expensive calculations to be presented in subsequent work. We furthermore evaluate the energetic separation between the optically prepared singlet excited state and the correlated triplet pair state, as well as provide a real-space characterization of the latter, both of which are of key importance in the discussion of fission dynamics. We discuss our results in the context of recent experimental studies.
最近的时间分辨光谱实验表明，振子耦合在促进单重态裂变过程中起着至关重要的作用。在这项工作中，我们通过一个振子激子理论来揭示单重态裂变的机制。我们建立了一个模型，其中电子和振动自由度都被微观且非微扰地处理。我们以五苯作为单重态裂变的典型材料，将我们的理论与单晶体偏振分辨吸收的测量结果进行比较，并利用我们的模型来描述吸收带的激发态。特别关注了光物理可观测量相对于所使用的基大小的收敛性，通过这种方法我们确定了后续更昂贵计算所需的最佳基。我们还评估了光学制备的单重激发态和相关三重态对态之间的能量分离，以及对后者的实空间描述，这两者在裂变动力学的讨论中都非常重要。我们在最近的实验研究的背景下讨论了我们的结果。
