Excited-State Reaction Dynamics of Bacteriochlorophyll Dimers

9728134贝克本研究项目的目的是测试的假设，细菌叶绿素二聚体在不对称的蛋白质环境中填充内二聚体电荷转移状态后，较低的激子状态的光学准备。 为了验证这一假设，研究人员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Rhododocellum rubrum G9中分离的LH 1捕光复合物B820亚基中的细菌叶绿素a二聚体，以及碳菁染料3，3 '-二乙基硫代三碘化碳菁（DTTCI）。 动态吸收光谱将被用来表征调制的光漂白和受激发射信号所产生的相干波包运动的基态和激发态，分别。 受激光子回波和瞬态光栅光谱将用于检查电子退相的初始准备状态。 B820所表现出的波包运动将被比较所表现出的单体细菌叶绿素a和完整的LH 1环系统，其中二聚体-二聚体相互作用被认为是重要的，看看如果在B820中观察到的表面交叉动力学是特定的细菌叶绿素二聚体。 拟议的工作的长期目标是获得一个详细的了解在两个目标系统中的电荷转移的动力学方面的势能面所涉及的和在振动模式，促进反应。 该研究项目将使用飞秒脉冲光的激光光谱学来研究电子如何在成对的细菌叶绿素分子中转移。 细菌叶绿素分子被光合植物和细菌用于捕光结构和反应中心，其中一些吸收光的能量被转化为化学能。 来自紫色细菌的反应中心的结构包含一对细菌叶绿素分子，它们充当导致能量储存的快速事件的触发点。 该研究项目的工作将研究一种简单的含细菌叶绿素的蛋白质和一种重要类型的有机染料中的反应;这两种系统都表现出非常快的电子转移反应，在吸收光后立即发生。 除了有助于理解光合作用的光反应机制外，该研究项目还将有助于全面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光吸收分子如何在材料中进行物理组织，以获得储能设备或新型催化剂。

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.