Erić Vesna, Li Xinmeng, Dsouza Lolita, Huijser Annemarie, Holzwarth Alfred R, Buda Francesco, Sevink G J Agur, de Groot Huub J M, Jansen Thomas L C
Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands.
Department of Chemistry and Hylleraas Centre for Quantum Molecular Sciences, University of Oslo, Sem Sælands vei 26, 0315 Oslo, Norway.
J Phys Chem B. 2024 Apr 18;128(15):3575-3584. doi: 10.1021/acs.jpcb.4c00067. Epub 2024 Apr 3.
Observations of low-lying dark states in several photosynthetic complexes challenge our understanding of the mechanisms behind their efficient energy transfer processes. Computational models are necessary for providing novel insights into the nature and function of dark states, especially since these are not directly accessible in spectroscopy experiments. Here, we will focus on signatures of dark-type states in chlorosomes, a light-harvesting complex from green sulfur bacteria well-known for uniting a broad absorption band with very efficient energy transfer. In agreement with experiments, our simulations of two-dimensional electronic spectra capture the ultrafast exciton transfer occurring in 100s of femtoseconds within a single chlorosome cylinder. The sub-100 fs process corresponds to relaxation within the single-excitation manifold in a single chlorosome tube, where all initially created populations in the bright exciton states are quickly transferred to dark-type exciton states. Structural inhomogeneities on the local scale cause a redistribution of the oscillator strength, leading to the emergence of these dark-type exciton states, which dominate ultrafast energy transfer. The presence of the dark-type exciton states suppresses energy loss from an isolated chlorosome via fluorescence quenching, as observed experimentally. Our results further question whether relaxation to dark-exciton states is a leading process or merely competes with transfer to the baseplate within the photosynthetic apparatus of green sulfur bacteria.
在几种光合复合物中对低位暗态的观察挑战了我们对其高效能量转移过程背后机制的理解。计算模型对于深入了解暗态的性质和功能至关重要，特别是因为这些在光谱实验中无法直接获取。在这里，我们将重点关注绿硫细菌的捕光复合物——叶绿体中暗态的特征，该复合物以结合宽吸收带和非常高效的能量转移而闻名。与实验结果一致，我们对二维电子光谱的模拟捕捉到了单个叶绿体圆柱体内在100飞秒内发生的超快激子转移。小于100飞秒的过程对应于单个叶绿体管内单重激发流形内的弛豫，其中最初在明亮激子态中产生的所有粒子迅速转移到暗态激子态。局部尺度上的结构不均匀性导致振子强度的重新分布，从而导致这些暗态激子态的出现，它们主导了超快能量转移。如实验观察到的那样，暗态激子态的存在通过荧光猝灭抑制了孤立叶绿体的能量损失。我们的结果进一步质疑弛豫到暗激子态是主要过程还是仅仅与绿硫细菌光合装置内转移到底板的过程竞争。
