Alfonso Hernandez Laura, Nelson Tammie, Tretiak Sergei, Fernandez-Alberti Sebastian
†Universidad Nacional de Quilmes, Roque Saenz Peña 352, B1876BXD Bernal, Argentina.
‡Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
J Phys Chem B. 2015 Jun 18;119(24):7242-52. doi: 10.1021/jp510557f. Epub 2015 Jan 8.
Nonadiabatic excited-state molecular dynamics (NA-ESMD) simulations have been performed in order to study the time-dependent exciton localization during energy transfer between two chromophore units of the weakly coupled anthracene dimer dithia-anthracenophane (DTA). Simulations are done at both low temperature (10 K) and room temperature (300 K). The initial photoexcitation creates an exciton which is primarily localized on a single monomer unit. Subsequently, the exciton experiences an ultrafast energy transfer becoming localized on either one monomer unit or the other, whereas delocalization between both monomers never occurs. In half of the trajectories, the electronic transition density becomes completely localized on the same monomer as the initial excitation, while in the other half, it becomes completely localized on the opposite monomer. In this article, we present an analysis of the energy transfer dynamics and the effect of thermally induced geometry distortions on the exciton localization. Finally, simulated fluorescence anisotropy decay curves for both DTA and the monomer unit dimethyl anthracene (DMA) are compared. Our analysis reveals that changes in the transition density localization caused by energy transfer between two monomers in DTA is not the only source of depolarization and exciton relaxation within a single DTA monomer unit can also cause reorientation of the transition dipole.
为了研究弱耦合蒽二聚体二硫代蒽并菲（DTA）的两个发色团单元之间能量转移过程中随时间变化的激子局域化，进行了非绝热激发态分子动力学（NA-ESMD）模拟。模拟在低温（10 K）和室温（300 K）下进行。初始光激发产生一个激子，该激子主要局域在单个单体单元上。随后，激子经历超快能量转移，局域在其中一个单体单元上，而两个单体之间从未发生离域。在一半的轨迹中，电子跃迁密度完全局域在与初始激发相同的单体上，而在另一半轨迹中，它完全局域在相反的单体上。在本文中，我们对能量转移动力学以及热诱导几何畸变对激子局域化的影响进行了分析。最后，比较了DTA和单体单元二甲基蒽（DMA）的模拟荧光各向异性衰减曲线。我们的分析表明，DTA中两个单体之间的能量转移引起的跃迁密度局域化变化不是去极化的唯一来源，单个DTA单体单元内的激子弛豫也会导致跃迁偶极的重新取向。
