Department of Chemistry and Center for Materials Chemistry, University of Houston, Houston, Texas 77204-5003, USA.
J Chem Phys. 2009 Nov 21;131(19):194905. doi: 10.1063/1.3259549.
We report upon a theoretical study of singlet exciton migration and relaxation within a model conjugated polymer chain. Starting from poly[2-methoxy-5-((2-ethylhexyl)oxy)-1,4-phenylenevinylene] polymer chains, we assume that the pi-conjugation is disrupted by conformational disorder of the chain itself, giving rise to a localized Frenkel exciton basis. Electronic coupling between segments as determined by the coupling between the transition densities of the localized excitons gives rise to delocalized exciton states. Using a kinetic Monte Carlo approach to compute the exciton transfer kinetics within the manifold of either the dressed chromophore site basis or dressed eigenstate basis, we find that the decay of the polarization anisotropy of the exciton is profoundly affected by the delocalization of the exciton over multiple basis segments. Two time scales emerge from the exciton migration simulations: a short, roughly 10 ps, time scale corresponding to rapid hopping about the initial excitation site followed by a slower, 180 ps, component corresponding to long range hopping. We also find that excitations can become trapped at long times when the hopping rate to lower-energy states is longer than the radiative lifetime of the exciton.
我们报告了在模型共轭聚合物链中单重激子迁移和弛豫的理论研究。从聚[2-甲氧基-5-((2-乙基己基)氧基)-1,4-亚苯基乙烯]聚合物链开始，我们假设链本身的构象无序破坏了π共轭，导致局部的弗伦克尔激子基础。通过局部激子的跃迁密度之间的耦合确定的片段之间的电子耦合导致离域激子态。使用动力学蒙特卡罗方法在修饰的发色团位点基础或修饰的本征态基础的组合内计算激子转移动力学，我们发现激子的极化各向异性的衰减被激子在多个基础片段上的离域深刻影响。激子迁移模拟中出现了两个时间尺度：一个短的，大约 10 ps，对应于初始激发点的快速跳跃，随后是一个较慢的，180 ps，对应于长程跳跃。我们还发现，当低能态的跃迁率长于激子的辐射寿命时，激发可以在长时间内被捕获。
