Padula Daniele, Lee Myeong H, Claridge Kirsten, Troisi Alessandro
Department of Chemistry, University of Warwick , Coventry CV4 7AL, U.K.
Department of Chemistry and Materials Innovation Factory, University of Liverpool , Liverpool L69 7ZD, U.K.
J Phys Chem B. 2017 Nov 2;121(43):10026-10035. doi: 10.1021/acs.jpcb.7b08020. Epub 2017 Oct 18.
In this paper, we adopt an approach suitable for monitoring the time evolution of the intramolecular contribution to the spectral density of a set of identical chromophores embedded in their respective environments. We apply the proposed method to the Fenna-Matthews-Olson (FMO) complex, with the objective to quantify the differences among site-dependent spectral densities and the impact of such differences on the exciton dynamics of the system. Our approach takes advantage of the vertical gradient approximation to reduce the computational demands of the normal modes analysis. We show that the region of the spectral density that is believed to strongly influence the exciton dynamics changes significantly in the timescale of tens of nanoseconds. We then studied the impact of the intramolecular vibrations on the exciton dynamics by considering a model of FMO in a vibronic basis and neglecting the interaction with the environment to isolate the role of the intramolecular exciton-vibration coupling. In agreement with the assumptions in the literature, we demonstrate that high frequency modes at energy much larger than the excitonic energy splitting have negligible influence on exciton dynamics despite the large exciton-vibration coupling. We also find that the impact of including the site-dependent spectral densities on exciton dynamics is not very significant, indicating that it may be acceptable to apply the same spectral density on all sites. However, care needs to be taken for the description of the exciton-vibrational coupling in the low frequency part of intramolecular modes because exciton dynamics is more susceptible to low frequency modes despite their small Huang-Rhys factors.
在本文中，我们采用了一种适用于监测嵌入各自环境中的一组相同发色团的光谱密度的分子内贡献随时间演化的方法。我们将所提出的方法应用于费纳 - 马修斯 - 奥尔森（FMO）复合物，目的是量化位点相关光谱密度之间的差异以及这些差异对系统激子动力学的影响。我们的方法利用垂直梯度近似来降低正常模式分析的计算需求。我们表明，据信对激子动力学有强烈影响的光谱密度区域在几十纳秒的时间尺度上会发生显著变化。然后，我们通过考虑在振动基下的FMO模型并忽略与环境的相互作用以分离分子内激子 - 振动耦合的作用，研究了分子内振动对激子动力学的影响。与文献中的假设一致，我们证明，尽管激子 - 振动耦合很大，但能量远大于激子能量分裂的高频模式对激子动力学的影响可忽略不计。我们还发现，纳入位点相关光谱密度对激子动力学的影响不是非常显著，这表明在所有位点应用相同的光谱密度可能是可以接受的。然而，对于分子内模式低频部分的激子 - 振动耦合的描述需要谨慎，因为尽管低频模式的黄 - 里斯因子较小，但激子动力学对其更敏感。
