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Coherent exciton transport driven by torsional dynamics: a quantum dynamical study of phenylene-vinylene type conjugated systems

机译:扭转动力学驱动的相干激子输运:亚苯基-亚乙烯基共轭体系的量子动力学研究

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摘要

We present a quantumdynamical study of exciton transfer across a torsional defect that locally breaks the π-conjugation in an oligo-(p-phenylene vinylene) (OPV) fragment. A site-based vibronic coupling Hamiltonian is used which is formulated in a comparative fashion (i) for a Frenkel exciton basis, assuming localized electron-hole pairs whose superposition yields a delocalized exciton, and (ii) more accurately, for a Merrifield type exciton basis including spatially separated electron-hole pairs. Starting from a partially delocalized (“spectroscopic unit”) initial condition, the observed transfer dynamics is found to involve two characteristic time scales: (i) a very rapid, coherent transient on a 10–100 femtosecond scale, largely determined by Rabi type oscillations modulated by bond-length-alternation modes, and (ii) a slower time scale involving the planarization of the torsional coordinates that determines the onset of a quasi-stationary exciton-polaron state, and in the process leads to a “healing” of the torsional defect within ~ 500 femtoseconds. The dynamics obtained from the full electron-hole basis vs. Frenkel basis are in good agreement. In the full electron-hole dynamics, the transients are found to involve a rapid expansion and subsequent contraction of the electron-hole coherence size. Quantum dynamical simulations for a minimal six-site model involving 36 states and 22 vibrational modes, were carried out using the multiconfiguration time dependent Hartree (MCTDH) method.
机译:我们提出了一个通过扭转缺陷进行激子转移的量子动力学研究,该缺陷局部破坏了寡聚-(对亚苯基亚乙烯基)(OPV)片段中的π共轭。使用基于位置的振动耦合哈密顿量,其以比较方式公式化:(i)以弗伦克尔激子为基础,假定局部电子-空穴对的叠加产生离域激子,以及(ii)更精确地为Merrifield型激子基础包括空间分离的电子-空穴对。从局部离域(“光谱单位”)的初始条件开始,发现观察到的传输动力学涉及两个特征时间尺度:(i)10-100飞秒尺度上的非常快速,相干的瞬变,主要由拉比型振荡决定通过键长交替模式进行调制,以及(ii)较慢的时标,涉及确定准静态激子-极化子态发生的扭转坐标的平面化,并在此过程中导致“治愈”。扭转缺陷在500飞秒以内。从全电子空穴基础相对于弗伦克尔基​​础获得的动力学具有很好的一致性。在全电子空穴动力学中,发现瞬变涉及电子空穴相干尺寸的快速膨胀和随后的收缩。使用多配置时间相关Hartree(MCTDH)方法对涉及36个状态和22个振动模式的最小六点模型进行了量子动力学仿真。

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