Lüttig Julian, Brixner Tobias, Malý Pavel
Institut für Physikalische und Theoretische Chemie, Am Hubland, 97074 Würzburg, Germany.
J Chem Phys. 2021 Apr 21;154(15):154202. doi: 10.1063/5.0046894.
Exciton-exciton-interaction two-dimensional (EEI2D) spectroscopy is a fifth-order variant of 2D electronic spectroscopy. It can be used to probe biexciton dynamics in molecular systems and to observe exciton diffusion in extended systems such as polymers or light-harvesting complexes. The exciton transport strongly depends on the geometrical and energetic landscape and its perturbations. These can be of both local character, such as molecular orientation and energetic disorder, and long-range character, such as polymer kinks and structural domains. In the present theoretical work, we investigate the anisotropy in EEI2D spectroscopy. We introduce a general approach for how to calculate the anisotropy by using the response-function formalism in an efficient way. In numerical simulations, using a Frenkel exciton model with Redfield-theory dynamics, we demonstrate how the measurement of anisotropy in EEI2D spectroscopy can be used to identify various geometrical effects on exciton transport in dimers and polymers. Investigating a molecular heterodimer as an example, we demonstrate the utility of anisotropy in EEI2D spectroscopy for disentangling dynamic localization and annihilation. We further calculate the annihilation in extended systems such as conjugated polymers. In a polymer, a change in the anisotropy provides a unique signature for exciton transport between differently oriented sections. We analyze three types of geometry variations in polymers: a kink, varying geometric and energetic disorder, and different geometric domains. Our findings underline that employing anisotropy in EEI2D spectroscopy provides a way to distinguish between different geometries and can be used to obtain a better understanding of long-range exciton transport.
激子 - 激子相互作用二维（EEI2D）光谱是二维电子光谱的五阶变体。它可用于探测分子系统中的双激子动力学，并观察聚合物或光捕获复合物等扩展系统中的激子扩散。激子传输强烈依赖于几何和能量景观及其扰动。这些扰动既可以是局部性质的，如分子取向和能量无序，也可以是长程性质的，如聚合物扭结和结构域。在当前的理论工作中，我们研究了EEI2D光谱中的各向异性。我们介绍了一种通过有效使用响应函数形式来计算各向异性的通用方法。在数值模拟中，我们使用具有雷德菲尔德理论动力学的弗伦克尔激子模型，展示了如何利用EEI2D光谱中的各向异性测量来识别二聚体和聚合物中激子传输的各种几何效应。以分子异二聚体为例进行研究，我们证明了EEI2D光谱中各向异性在解开动态定位和湮灭方面的效用。我们还进一步计算了共轭聚合物等扩展系统中的湮灭。在聚合物中，各向异性的变化为不同取向部分之间的激子传输提供了独特的特征。我们分析了聚合物中的三种几何变化类型：扭结、变化的几何和能量无序以及不同的几何域。我们的研究结果强调，在EEI2D光谱中采用各向异性提供了一种区分不同几何形状的方法，可用于更好地理解长程激子传输。
