Institut für Physik, Humboldt-Universität zu Berlin, Newtonstrasse 15, D-12489, Berlin, Germany.
Dalton Trans. 2009 Dec 7(45):10086-105. doi: 10.1039/b908567j. Epub 2009 Sep 9.
Electronic excitation energy transfer in molecular systems is connected with the de-excitation of one molecule and the excitation of the other. Mostly, it can be understood in terms of Förster (or fluorescence) resonance energy transfer. An increasing interest in the optimization of artificial light harvesting systems, however, requires a more detailed study going beyond the standard Förster scheme. There are two main routes to do this. Considering a Coulombic less-strongly coupled system first, coherences among different chromophores may be considered in the framework of perturbation theory with higher-order mechanisms correcting the standard second-order description. Secondly, if inter-chromophore coherences are dominant and delocalized Frenkel-exciton states are formed, it becomes of some importance to study their decay due to the coupling to vibrational degrees of freedom. While we will also comment on this latter mechanism, the first description based on localized excitations will be the main focus. A general higher-order theory resulting in respective transition rates and rate equations is utilized. Its capability is demonstrated when presenting a systematic description of short-range and long-range corrections to the basic Förster mechanism. Accordingly, a unique description of bridge-mediated and photon-mediated long-range electronic excitation energy transfer is offered. Moreover, short-range excitation energy transfer appearing as a two electron exchange is also discussed. And, the exciton-exciton annihilation process present at higher optical excitation intensities is described as a direct higher-order transition. The related higher-order vibrational correlation functions are presented and estimated for the reference case where the coupling to vibrational degrees of freedom either of intra-molecular or inter-molecular type is reduced to a simple electronic state dephasing process.
分子体系中的电子激发能量转移与一个分子的去激发和另一个分子的激发有关。在大多数情况下，可以用福斯特（Förster）（或荧光）共振能量转移来理解。然而，对人工光捕获系统的优化的日益关注需要更详细的研究，超越标准的福斯特方案。有两种主要的方法可以做到这一点。首先考虑一个库仑较弱耦合的系统，可以在更高阶机制的微扰理论框架中考虑不同发色团之间的相干性，以修正标准的二阶描述。其次，如果发色团之间的相干性占主导地位并且形成了离域的弗伦克尔激子态，那么由于与振动自由度的耦合，研究它们的衰减就变得很重要。虽然我们也将评论后一种机制，但基于局域激发的第一种描述将是主要关注点。利用产生相应跃迁速率和速率方程的一般高阶理论。当呈现对基本福斯特机制的短程和长程修正的系统描述时，证明了其能力。因此，提供了桥介导和光子介导长程电子激发能量转移的独特描述。此外，还讨论了作为双电子交换出现的短程激发能量转移。并且，在较高的光激发强度下出现的激子激子湮灭过程被描述为直接的高阶跃迁。呈现并估计了相关的高阶振动相关函数，作为参考情况，其中分子内或分子间类型的振动自由度的耦合简化为电子态退相过程。
