Andrews David L, Leeder Jamie M
Nanostructures and Photomolecular Systems, School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
J Chem Phys. 2009 May 14;130(18):184504. doi: 10.1063/1.3131168.
The Coulombic coupling of electric dipole (E1) transition moments is the most commonly studied and widely operative mechanism for energy migration in multichromophore systems. However a significant number of exceptions exist, in which donor decay and/or acceptor excitation processes are E1-forbidden. The alternative transfer mechanisms that can apply in such cases include roles for higher multipole transitions, exciton- or phonon-assisted interactions, and non-Coulombic interactions based on electron exchange. A quantum electrodynamical formulation provides a rigorous basis to assess the first of these, specifically addressing the relative significance of higher multipole contributions to the process of energy transfer in donor-acceptor systems where electric dipole transitions are precluded by symmetry. Working within the near-zone limit, where donor-acceptor separations are small in comparison to the chromophore scale, the analysis highlights the contributions of both electric quadrupole-electric quadrupole (E2-E2) coupling and the seldom considered second-order electric dipole-electric dipole (E1(2)-E1(2)) coupling. For both forms of interaction, experimentally meaningful rate equations are secured by the use of orientational averaging, and the mechanisms are analyzed with reference to systems in which E1-forbidden transitions are commonly reported.
电偶极（E1）跃迁矩的库仑耦合是多发色团系统中能量迁移最常被研究且广泛起作用的机制。然而，存在大量例外情况，其中供体衰变和/或受体激发过程是E1禁阻的。在这种情况下可适用的替代转移机制包括更高阶多极跃迁、激子或声子辅助相互作用以及基于电子交换的非库仑相互作用所起的作用。量子电动力学公式为评估其中第一个机制提供了严格基础，具体解决了在对称禁阻电偶极跃迁的供体 - 受体系统中，更高阶多极对能量转移过程贡献的相对重要性。在近区极限内工作，即供体 - 受体间距与发色团尺度相比很小时，分析突出了电四极 - 电四极（E2 - E2）耦合以及很少被考虑的二阶电偶极 - 电偶极（E1(2) - E1(2)）耦合的贡献。对于这两种相互作用形式，通过使用取向平均获得了具有实验意义的速率方程，并参考了通常报道E1禁阻跃迁的系统对这些机制进行了分析。
