Gonzalvez Perez Isabel, Barford William
Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom.
J Phys Chem Lett. 2021 Jun 10;12(22):5344-5348. doi: 10.1021/acs.jpclett.1c01354. Epub 2021 Jun 2.
We report on large-scale simulations of intrachain exciton dynamics in poly(-phenylenevinylene). Our theoretical model describes Frenkel exciton coupling to both fast, quantized C-C bond vibrations and slow, classical torsional modes. We also incorporate system-bath interactions. The dynamics is simulated using the time evolution block decimation method, which avoids the failures of the Ehrenfest approximation to describe decoherence processes and nonadiabatic interstate conversion. System-bath interactions are modeled using quantum trajectories and Lindblad quantum jump operators. We find that following photoexcitation, the quantum mechanical entanglement of the exciton and C-C bond phonons causes exciton-site decoherence. Next, system-bath interactions cause the stochastic collapse of high-energy delocalized excitons into chromophores. Finally, torsional relaxation causes additional exciton-density localization. We relate these dynamical processes to the predicted fluorescence depolarization, extract the time scales corresponding to them, and thus interpret the observed sub-ps fluorescence depolarization.
我们报道了聚（对苯撑乙烯）链内激子动力学的大规模模拟。我们的理论模型描述了弗伦克尔激子与快速的、量子化的C-C键振动以及缓慢的、经典的扭转模式之间的耦合。我们还考虑了系统与环境的相互作用。使用时间演化块抽取方法模拟动力学，该方法避免了埃伦费斯特近似在描述退相干过程和非绝热态间转换时的失效。利用量子轨迹和林德布拉德量子跳跃算符对系统与环境的相互作用进行建模。我们发现，光激发后，激子与C-C键声子的量子力学纠缠导致激子-位点退相干。接下来，系统与环境的相互作用导致高能离域激子随机坍缩到发色团中。最后，扭转弛豫导致激子密度进一步局域化。我们将这些动力学过程与预测的荧光去极化联系起来，提取与之对应的时间尺度，从而解释观测到的亚皮秒荧光去极化现象。
