Department of Chemical Physics, Lund University, Getingevägen 60, 221 00 Lund, Sweden.
J Am Chem Soc. 2012 Jul 18;134(28):11611-7. doi: 10.1021/ja3025627. Epub 2012 Jul 2.
Chlorosomes are light-harvesting antennae that enable exceptionally efficient light energy capture and excitation transfer. They are found in certain photosynthetic bacteria, some of which live in extremely low-light environments. In this work, chlorosomes from the green sulfur bacterium Chlorobaculum tepidum were studied by coherent electronic two-dimensional (2D) spectroscopy. Previously uncharacterized ultrafast energy transfer dynamics were followed, appearing as evolution of the 2D spectral line-shape during the first 200 fs after excitation. Observed initial energy flow through the chlorosome is well explained by effective exciton diffusion on a sub-100 fs time scale, which assures efficiency and robustness of the process. The ultrafast incoherent diffusion-like behavior of the excitons points to a disordered energy landscape in the chlorosome, which leads to a rapid loss of excitonic coherences between its structural subunits. This disorder prevents observation of excitonic coherences in the experimental data and implies that the chlorosome as a whole does not function as a coherent light-harvester.
叶绿素体是一种光收集天线，能够实现极高效率的光能捕获和激发能量转移。它们存在于某些光合细菌中，其中一些生活在极低光环境中。在这项工作中，通过相干电子二维（2D）光谱研究了绿硫细菌 Chlorobaculum tepidum 的叶绿素体。跟踪了以前未表征的超快能量转移动力学，表现为激发后最初 200fs 内 2D 光谱线形状的演化。通过在亚 100fs 的时间尺度上有效激子扩散，很好地解释了观察到的初始能量流，这确保了该过程的效率和稳健性。激子的超快非相干扩散行为表明叶绿素体中存在无序的能量景观，导致其结构亚基之间的激子相干迅速丧失。这种无序现象阻止了在实验数据中观察到激子相干，这意味着叶绿素体作为一个整体不能作为相干光收集器。
