Excited-State Reaction Dynamics of Bacteriochlorophyll Dimers

本研究项目旨在验证不对称蛋白质环境下细菌叶绿素二聚体在光学制备低激子态后填充于内含物电荷转移态的假设。为了验证这一假设，研究者将表征两个不对称系统中光诱导电荷转移过程中产生的激发态相干波包运动：从红红螺旋藻G9中分离出来的LH1光捕获复合物B820亚基中的细菌叶绿素a二聚体，以及碳青染料3,3'-二乙基硫代-碘化碳青（DTTCI）。动态吸收光谱学将分别用于表征由相干波包在基态和激发态运动产生的光漂白和刺激发射信号的调制。受激光子回波和瞬态光栅光谱学将用于检测初始制备态的电子消相。B820所表现出的波包运动将与单体细菌叶绿素a和完整的LH1环系统所表现出的波包运动进行比较，其中二聚体-二聚体相互作用被认为是重要的，以确定在B820中观察到的表面交叉动力学是否特定于细菌叶绿素二聚体。所提出的工作的长期目标是根据所涉及的势能表面和促进反应的振动模式，获得两个目标系统中电荷转移动力学的详细理解。这个研究项目将使用激光光谱学和飞秒光脉冲来研究电子是如何成对地在细菌叶绿素分子中转移的。细菌叶绿素分子被光合植物和细菌用于光收集结构和反应中心，在那里吸收的光的一些能量转化为化学能。紫色细菌的反应中心结构包含一对叶绿素分子，它们是导致能量储存的快速事件的触发点。本研究项目将研究一种简单的细菌含叶绿素蛋白质和一种重要的有机染料中的反应；两种体系都表现出非常快的电子转移反应，发生在吸收光之后。除了有助于了解光合作用的光反应机制外，该研究项目还将有助于了解太阳能如何通过化学系统转化为储存形式的能量。从长远来看，该项目将有助于确定吸收光的分子如何在材料中进行物理组织，以获得储能装置或新型催化剂。

9728134 Beck This research project is designed to test the hypothesis that bacteriochlorophyll dimers in asymmetric protein environments populate intradimer charge-transfer states after optical preparation of the lower exciton state. In order to test this hypothesis, the investigator will characterize the excited-state coherent wavepacket motions that arise during light-induced charge transfer in two asymmetric systems: the bacteriochlorophyll a dimer in the B820 subunit of the LH1 light-harvesting complex, as isolated from Rhodospirillum rubrum G9, and the carbocyanine dye 3,3'-diethylthiatri-carbocyanine iodide (DTTCI). Dynamic absorption spectroscopy will be used to characterize the modulations of the photobleaching and stimulated-emission signals that arise from coherent wavepacket motion on the ground and excited states, respectively. Stimulated-photon-echo and transient-grating spectroscopy will be used to examine the electronic dephasing of the initially prepared state. The wavepacket motions exhibited by B820 will be compared to those exhibited by monomeric bacteriochlorophyll a and by the intact LH1 ring system, where dimer-dimer interactions are thought to be important, to see if the surface-crossing dynamics observed in B820 are specific to bacteriochlorophyll dimers. The long-term goal of the proposed work is to obtain a detailed understanding of the dynamics of charge transfer in both target systems in terms of the potential-energy surfaces that are involved and in terms of the vibrational modes that promote the reaction. This research project will use laser spectroscopy with femtosecond pulses of light to study how electrons are transferred in pairs of bacteriochlorophyll molecules. Bacteriochlorophyll molecules are used by photosynthetic plants and bacteria in light-harvesting structures and in reaction centers, where some of the energy of the absorbed light is converted to chemical energy. The structure of the reaction center from purple bacteria contains a pair of ba cteriochlorophyll molecules that act as the trigger point for the fast events that lead to storage of energy. The work in this research project will study reactions in a simple bacteriochlorophyll-containing protein and in an important type of organic dye; both systems exhibit very fast electron-transfer reactions that occur just after absorption of light. In addition to contributing to the understanding of the mechanism of the light reactions of photosynthesis, this research project will contribute to the general understanding of how solar energy can be converted by chemical systems into stored forms of energy. In the long term, the project will help determine how light-absorbing molecules can be physically organized in materials to obtain energy-storing devices or novel catalysts.