Phycobilisomes are light-harvesting complexes that play a key role in photosynthesis in cyanobacteria, which generate more than 40% of the world’s oxygen. The near-unity excitation energy transfer efficiency from phycobilisomes to photosystems highlights its importance in understanding efficient energy transfer processes. Spectroscopic studies have shown that the 280 fs rapid excitonic downhill energy transfer within the α₈₄-β₈₄ chromophore dimer in allophycocyanin (APC), a subunit of phycobilisomes, is crucial to this efficiency. However, the role of strong chromophore–protein interactions and vibrational relaxation requires further exploration to fully explain this efficient downhill energy transfer. A theory is required that adequately describes exciton dynamics in an intermediate region while also incorporating vibrational relaxation mediated by protein bath modes. In this work, we incorporate vibrational relaxation into modified Redfield theory by introducing coupling fluctuation. We holistically simulate the rapid excitation energy transfer process of the α₈₄-β₈₄ chromophore dimer in APC and successfully model the recently observed rapid energy capture. We find that vibrational relaxation dictates capture of excitons by the localized state of the β₈₄ chromophore. The calculated rate shows excellent agreement with previous ultrafast spectroscopic experiments. Our results show that the inclusion of vibrational relaxation is essential for systems that utilize vibronic coupling to enhance energy transfer and capture. Consequently, incorporating vibrational relaxation into Modified Redfield theory shows promise for accurately describing the excitation energy transfer process in other photosynthetic systems.

中文翻译：

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振动弛豫完成激发能转移和别藻蓝蛋白 α84-β84 中振动激子的定位


藻胆体是光捕获复合物，在蓝藻的光合作用中起关键作用，蓝藻产生世界上 40% 以上的氧气。从藻胆体到光系统的近乎统一的激发能量转移效率突出了它在理解有效能量转移过程方面的重要性。光谱研究表明，别藻蓝蛋白 （APC）（藻胆素的一个亚基）中_{α 84-β 84} 发色团二聚体内的 280 fs 快速激子下坡能量转移对这种效率至关重要。然而，强发色团-蛋白质相互作用和振动弛豫的作用需要进一步探索，以充分解释这种有效的下坡能量转移。需要一种理论来充分描述中间区域中的激子动力学，同时还要结合由蛋白质浴模式介导的振动弛豫。在这项工作中，我们通过引入耦合波动，将振动弛豫纳入改进的 Redfield 理论中。我们全面模拟了 APC 中 α_{84-β 84} 发色团二聚体的快速激发能量转移过程，并成功模拟了最近观察到的快速能量捕获。我们发现振动弛豫决定了 β₈₄ 发色团的局部状态对激子的捕获。计算的速率与之前的超快光谱实验非常吻合。我们的结果表明，对于利用振动耦合来增强能量传递和捕获的系统来说，包含振动弛豫是必不可少的。因此，将振动弛豫纳入修正红场理论有望准确描述其他光合系统中的激发能量传递过程。