Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Phys Chem B. 2009 Nov 19;113(46):15352-63. doi: 10.1021/jp9066586.
Photosynthetic light-harvesting complexes absorb energy and guide photoexcitations to reaction centers with speed and efficacy that produce near-perfect efficiency. Light harvesting complex II (LHCII) is the most abundant light-harvesting complex and is responsible for absorbing the majority of light energy in plants. We apply two-dimensional electronic spectroscopy to examine energy flow in LHCII. This technique allows for direct mapping of excitation energy pathways as a function of absorption and emission wavelength. The experimental and theoretical results reveal that excitation energy transfers through the complex on three time scales: previously unobserved sub-100 fs relaxation through spatially overlapping states, several hundred femtosecond transfer between nearby chlorophylls, and picosecond energy transfer steps between layers of pigments. All energy is observed to collect into the energetically lowest and most delocalized states, which serve as exit sites. We examine the angular distribution of optimal energy transfer produced by this delocalized electronic structure and discuss how it facilitates the exit step in which the energy moves from LHCII to other complexes toward the reaction center.
光合作用光捕获复合物以速度和效率吸收能量并引导光激发至反应中心，从而产生近乎完美的效率。光捕获复合物 II（LHCII）是最丰富的光捕获复合物，负责吸收植物中大部分的光能。我们应用二维电子光谱来研究 LHCII 中的能量流动。这项技术允许直接绘制激发能量途径作为吸收和发射波长的函数。实验和理论结果表明，激发能量通过复合物在三个时间尺度上转移：以前未观察到的通过空间重叠态的亚 100fs 弛豫，数百飞秒在附近叶绿素之间的转移，以及在颜料层之间的皮秒能量转移步骤。所有能量都被观察到收集到能量最低和最离域的状态，这些状态作为出口位点。我们研究了这种离域电子结构产生的最佳能量转移的角分布，并讨论了它如何促进能量从 LHCII 转移到其他复合物到反应中心的出口步骤。
