Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany.
I. Institut für Theoretische Physik, Universität Hamburg, Jungiusstraße 9, 20355 Hamburg, Germany.
J Chem Phys. 2019 Sep 21;151(11):114115. doi: 10.1063/1.5119248.
The light-harvesting efficiency of a photoactive molecular complex is largely determined by the properties of its electronic quantum states. Those, in turn, are influenced by molecular vibrational states of the nuclear degrees of freedom. Here, we reexamine two recently formulated concepts that a coherent vibronic coupling between molecular states would either extend the electronic coherence lifetime or enhance the amplitude of the anticorrelated vibrational mode at longer times. For this, we study a vibronically coupled dimer and calculate the nonlinear two-dimensional (2D) electronic spectra that directly reveal electronic coherence. The time scale of electronic coherence is initially extracted by measuring the antidiagonal bandwidth of the central peak in the 2D spectrum at zero waiting time. Based on the residual analysis, we identify small-amplitude long-lived oscillations in the cross-peaks, which, however, are solely due to groundstate vibrational coherence, regardless of having resonant or off-resonant conditions. Our studies neither show an enhancement of the electronic quantum coherence nor an enhancement of the anticorrelated vibrational mode by the vibronic coupling under ambient conditions.
光活性分子配合物的光捕获效率在很大程度上取决于其电子量子态的性质。而这些性质又受到核自由度分子振动态的影响。在这里，我们重新审视了两个最近提出的概念，即分子态之间的相干振子耦合要么会延长电子相干寿命，要么会在更长的时间内增强相关振动模式的幅度。为此，我们研究了一个振子耦合的二聚体，并计算了直接揭示电子相干性的非线性二维（2D）电子光谱。在零等待时间下，通过测量 2D 光谱中中心峰的反对角线带宽来初始提取电子相干时间尺度。基于残差分析，我们在交叉峰中识别出小振幅长寿命的振荡，但这些振荡仅归因于基态振动相干性，而与共振或非共振条件无关。我们的研究既没有显示出电子量子相干性的增强，也没有显示出在环境条件下通过振子耦合增强相关振动模式。
