Department of Biophysics, Faculty of Sciences, Vrije Universiteit Amsterdam and LaserLaB Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Phys Chem Chem Phys. 2020 Nov 18;22(44):25720-25729. doi: 10.1039/d0cp03351k.
The Lhca4 antenna complex of plant Photosystem I (PSI) is characterized by extremely red-shifted and broadened absorption and emission bands from its low-energy chlorophylls (Chls). The mixing of a charge-transfer (CT) state with the excited state manifold causing these so-called red forms results in highly complicated multi-component excited energy transfer (EET) kinetics within the complex. The two-dimensional electronic spectroscopy experiments presented here reveal that EET towards the CT state occurs on three timescales: fast from the red Chls (within 1 ps), slower (5-7 ps) from the stromal side Chls, and very slow (100-200 ps) from a newly discovered 690 nm luminal trap. The excellent agreement between the experimental data with the previously presented Redfield-Förster exciton model of Lhca4 strongly supports the equilibration scheme of the bulk excitations with the dynamically localized CT on the stromal side. Thus, a complete picture of the energy transfer pathways leading to the population of the CT final trap within the whole Lhca4 complex is presented. In view of the environmental sensitivity of the CT contribution to the Lhca4 energy landscape, we speculate that one role of the CT states is to regulate the EET from the peripheral antenna to the PSI core.
植物光系统 I (PSI) 的 Lhca4 天线复合物的特征是其低能量叶绿素 (Chls) 的吸收和发射带具有非常明显的红移和展宽。电荷转移 (CT) 态与激发态分子轨道的混合导致了这些所谓的红形式，从而导致复合物内高度复杂的多组分激发能量转移 (EET) 动力学。这里呈现的二维电子光谱实验表明，CT 态的 EET 发生在三个时间尺度上：来自红色 Chls 的快速（<1 ps）、来自基质侧 Chls 的较慢（5-7 ps）以及来自新发现的 690nm 腔内陷阱的非常慢（100-200 ps）。实验数据与之前提出的 Lhca4 Redfield-Förster 激子模型之间的极好一致性强烈支持了大块激发与基质侧动态局部化 CT 之间的平衡方案。因此，呈现了导致整个 Lhca4 复合物中 CT 最终陷阱种群的能量转移途径的完整图景。鉴于 CT 对 Lhca4 能量景观的环境敏感性，我们推测 CT 态的一个作用是调节从外围天线到 PSI 核心的 EET。
