Beljonne David, Curutchet Carles, Scholes Gregory D, Silbey Robert J
Laboratory for Chemistry of Novel Materials, Center for Research on Molecular Electronics and Photonics, University of Mons-Hainaut, Place du Parc 20, B-7000 Mons Belgium.
J Phys Chem B. 2009 May 14;113(19):6583-99. doi: 10.1021/jp900708f.
After photoexcitation, energy absorbed by a molecule can be transferred efficiently over a distance of up to several tens of angstroms to another molecule by the process of resonance energy transfer, RET (also commonly known as electronic energy transfer, EET). Examples of where RET is observed include natural and artificial antennae for the capture and energy conversion of light, amplification of fluorescence-based sensors, optimization of organic light-emitting diodes, and the measurement of structure in biological systems (FRET). Forster theory has proven to be very successful at estimating the rate of RET in many donor-acceptor systems, but it has also been of interest to discover when this theory does not work. By identifying these cases, researchers have been able to obtain, sometimes surprising, insights into excited-state dynamics in complex systems. In this article, we consider various ways that electronic energy transfer is promoted by mechanisms beyond those explicitly considered in Forster RET theory. First, we recount the important situations when the electronic coupling is not accurately calculated by the dipole-dipole approximation. Second, we examine the related problem of how to describe solvent screening when the dipole approximation fails. Third, there are situations where we need to be careful about the separability of electronic coupling and spectral overlap factors. For example, when the donors and/or acceptors are molecular aggregates rather than individual molecules, then RET occurs between molecular exciton states and we must invoke generalized Forster theory (GFT). In even more complicated cases, involving the intermediate regime of electronic energy transfer, we should consider carefully nonequilibrium processes and coherences and how bath modes can be shared. Lastly, we discuss how information is obscured by various forms of energetic disorder in ensemble measurements and we outline how single molecule experiments continue to be important in these instances.
光激发后，分子吸收的能量可通过共振能量转移（RET，也通常称为电子能量转移，EET）过程有效地在长达几十埃的距离上转移到另一个分子。观察到RET的例子包括用于光捕获和能量转换的天然和人工天线、基于荧光的传感器的放大、有机发光二极管的优化以及生物系统中结构的测量（荧光共振能量转移）。福斯特理论已被证明在估计许多供体 - 受体系统中的RET速率方面非常成功，但发现该理论何时不适用也很有意义。通过识别这些情况，研究人员能够获得，有时是令人惊讶的，关于复杂系统中激发态动力学的见解。在本文中，我们考虑了除福斯特RET理论明确考虑的机制之外，电子能量转移被促进的各种方式。首先，我们叙述当电子耦合不能通过偶极 - 偶极近似准确计算时的重要情况。其次，我们研究当偶极近似失败时如何描述溶剂筛选这一相关问题。第三，存在一些情况，我们需要注意电子耦合和光谱重叠因子的可分离性。例如，当供体和/或受体是分子聚集体而不是单个分子时，那么RET发生在分子激子态之间，我们必须援引广义福斯特理论（GFT）。在更复杂的情况下，涉及电子能量转移的中间区域，我们应该仔细考虑非平衡过程和相干性以及浴模式如何共享。最后，我们讨论在系综测量中各种形式的能量无序如何掩盖信息，并且我们概述在这些情况下单分子实验如何仍然很重要。
