Institute of Physics, University of Rostock, Albert Einstein Straße 23-24, 18059 Rostock, Germany.
Chemical Physics and NanoLund, Lund University, P.O. Box 124, 22100 Lund, Sweden.
J Chem Phys. 2018 Sep 21;149(11):114107. doi: 10.1063/1.5046645.
Förster theory describes electronic exciton energy migration in molecular assemblies as an incoherent hopping process between donor and acceptor molecules. The rate is expressed in terms of the overlap integral between donor fluorescence and acceptor absorption spectra. Typical time scales for systems like photosynthetic antennae are on the order of a few picoseconds. Prior to transfer, it is assumed that the initially excited donor molecule has equilibrated with respect to the local environment. However, upon excitation and during the equilibration phase, the state of the system needs to be described by the full density matrix, including coherences between donor and acceptor states. While being intuitively clear, addressing this regime experimentally has been a challenge until the recently reported advances in fluorescence detected two-dimensional spectroscopy. Here, we demonstrate using fourth order perturbation theory the conditions for the presence of donor-acceptor coherence induced cross-peaks at zero waiting time between the first and the second pair of pulses. The approach is illustrated for a heterodimer model which facilitates an analytical solution.
福斯特理论将分子组装体中的电子激子能量迁移描述为供体和受体分子之间的非相干跃迁过程。速率用供体荧光和受体吸收光谱之间的重叠积分来表示。类似光合天线的系统的典型时间尺度为数皮秒。在转移之前，假设最初被激发的供体分子已经与局部环境达到平衡。然而，在激发和平衡阶段，系统的状态需要用完整的密度矩阵来描述，包括供体和受体状态之间的相干性。虽然直观上很清楚，但直到最近在荧光探测二维光谱方面的进展，实验上解决这个问题一直是一个挑战。在这里，我们使用四阶微扰理论证明了在第一对和第二对脉冲之间没有等待时间的情况下，存在供体-受体相干诱导交叉峰的条件。该方法通过一个异二聚体模型进行了说明，该模型便于获得解析解。
