J Phys Chem B. 2019 Jan 31;123(4):852-859. doi: 10.1021/acs.jpcb.8b12542. Epub 2019 Jan 16.
Excitonic interactions between two closely separated bacteriochlorophyll a molecules (BChls) in the special pair of the reaction center (RC) of purple bacteria determine the positions and relative oscillator strengths of its two excitonic components. While the absorption of the lower excitonic band is well-defined, the position and the intensity of the upper excitonic band ( P) are still under debate. Recent 77 K two-dimensional electronic spectroscopy data on Rba. capsulatus suggested that the P component absorbs at ∼840 nm, i.e., at a significantly lower energy than previously suggested. In the present work, we argue that the P state is mixed with the excited states of the accessory BChls ( B*/ P ) leading to excitons contributing to the 785-825 nm spectral region which is consistent with previously published data. This conclusion is based on hole-burning/linear dichroism data and modeling studies of the excitonic structure of the RC using a non-Markovian reduced density matrix approach.
两个紧密分离的细菌叶绿素 a 分子 (BChls) 在紫细菌反应中心 (RC) 的特殊对之间的激子相互作用决定了其两个激子分量的位置和相对振子强度。虽然较低激子带的吸收是明确的，但上激子带 (P) 的位置和强度仍存在争议。最近关于 Rba. capsulatus 的 77 K 二维电子光谱数据表明，P 分量在 ∼840nm 处吸收，即能量明显低于先前的建议。在本工作中，我们认为 P 态与辅助细菌叶绿素 (B*/P) 的激发态混合，导致贡献 785-825nm 光谱区域的激子，这与先前发表的数据一致。这一结论是基于孔烧蚀/线二色性数据和使用非马尔可夫约化密度矩阵方法对 RC 的激子结构进行的建模研究。
