Department of Biochemistry, University of Washington, Seattle, Washington 98195, United States.
J Phys Chem B. 2020 Mar 5;124(9):1733-1739. doi: 10.1021/acs.jpcb.0c00497. Epub 2020 Feb 26.
In the initial charge-separation reaction of photosynthetic bacterial reaction centers, a dimer of strongly interacting bacteriochlorophylls (P) transfers an electron to a third bacteriochlorophyll (B). It has been suggested that light first generates an exciton state of the dimer and that an electron then moves from one bacteriochlorophyll to the other within P to form a charge-transfer state (PP), which passes an electron to B. This scheme, however, is at odds with the most economical analysis of the spectroscopic properties of the reaction center and particularly with the unusual temperature dependence of the long-wavelength absorption band. The present paper explores this conflict with the aid of a simple model in which exciton and charge-transfer states are coupled to three vibrational modes. It then uses a similar model to show that the main experimental evidence suggesting the formation of PP as an intermediate could reflect pure dephasing of vibrational modes that modulate stimulated emission.
在光合细菌反应中心的初始电荷分离反应中，两个强烈相互作用的细菌叶绿素（P）二聚体将电子转移到第三个细菌叶绿素（B）上。有人认为，光首先产生二聚体的激子态，然后电子在 P 中从一个细菌叶绿素转移到另一个细菌叶绿素，形成电荷转移态（PP），PP 将电子传递给 B。然而，该方案与反应中心光谱性质的最经济分析以及长波长吸收带的异常温度依赖性相矛盾。本文借助于一个简单的模型，该模型将激子态和电荷转移态与三个振动模式耦合，探讨了这一冲突。然后，它使用类似的模型表明，形成 PP 作为中间态的主要实验证据可能反映了调节受激辐射的振动模式的纯退相。
