Deparment of Chemistry , University of Pennsylvania , 231 South 34 Street , Philadelphia , Pennsylvania 19104 , United States.
Department of Biochemistry and Molecular Biology , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States.
J Am Chem Soc. 2018 Sep 19;140(37):11631-11638. doi: 10.1021/jacs.8b04593. Epub 2018 Sep 5.
Photosystem I (PSI) is a naturally occurring light-harvesting complex that drives oxygenic photosynthesis through a series of photoinitiated transmembrane electron transfer reactions that occur with a high quantum efficiency. Understanding the mechanism by which this process occurs is fundamental to understanding the near-unity quantum efficiency of PSI and in turn could lead to further insight into PSI-based technologies for solar energy conversion. In this article, we have applied two-dimensional electronic spectroscopy to PSI complexes isolated from two different cyanobacterial strains to gain further insight into the ultrafast energy transfer in PSI. The PSI complexes studied differ in the number and absorption of the red chlorophylls, chlorophylls that lie to lower energies than the reaction center. By applying a global analysis to the 2D electronic spectra of the PSI complexes we extract 2D decay associated spectra (2D-DAS). Through analysis of the 2D-DAS we observe a 50 fs relaxation among the bulk antenna chlorophylls in addition to two pathways of energy equilibration involving the red chlorophylls: a fast 200 fs equilibration followed by a 2-4 ps equilibration. As demonstrated with a model system, the λ, λ coordinates of the cross-peaks in the 2D-DAS spectra indicate that the two equilibration pathways involve different chlorophyll molecules.
光系统 I（PSI）是一种天然存在的光捕获复合物，通过一系列光引发的跨膜电子转移反应驱动产氧光合作用，其具有很高的量子效率。了解该过程发生的机制对于理解 PSI 的近量子效率至关重要，并且可以进一步深入了解基于 PSI 的太阳能转换技术。在本文中，我们应用二维电子光谱学对来自两种不同蓝藻菌株的 PSI 复合物进行了研究，以进一步了解 PSI 中的超快能量转移。所研究的 PSI 复合物在数量和吸收红光叶绿素方面存在差异，而红光叶绿素的能量低于反应中心。通过对 PSI 复合物的二维电子光谱进行全局分析，我们提取了二维衰减相关光谱（2D-DAS）。通过对 2D-DAS 的分析，我们观察到在大量天线叶绿素之间存在 50 fs 的弛豫，此外还有两种涉及红光叶绿素的能量平衡途径：快速的 200 fs 平衡 followed by 2-4 ps 的平衡。通过模型系统证明，2D-DAS 光谱中交叉峰的 λ，λ 坐标表明两种平衡途径涉及不同的叶绿素分子。
