TIME RESOLVED INFRARED STUDIES OF ELECTRON TRANSFER COUPLED NUCLEAR ORGANIZATION

电子转移（ET）是自然界最重要的反应之一， 在呼吸和光合作用途径中起着关键作用， 基本的生物能量学意义。 虽然相对来说， 作为反应类别，ET反应在以下方面没有被详细理解： 定义反应性的分子特征：超快振动 光谱学（红外或相干光学）将提供第一直接 一种实验探针，将有助于破译分子运动是如何 与实际ET事件相关联。 重组能（l）由内层（高频）组成， 施主、受主和介质的振动模式）和外层 （溶剂或浴的低频振动模式）贡献，是 的主要意义，在确定如何快速ET发生在一个给定的 供体-受体系统我们的目标是真正识别和测量 振动模式的能量是ET反应坐标的关键 代表了一个尚未探索的实验前沿： 我们对电荷转移化学的基本知识， 影响了描述ET的理论框架 反应是巨大的。 我们的工作重点是简单的供体-受体复合物， 电荷分离和/或改变复合反应（kET大于 2 x 10[12] s-1）;快速ET的要求确保振动 激发态反应物以及基态和激发态的退相 ET产物不会在我们的实验时间尺度上发生。模型系统 其允许成对检查反应中心型发色团 (such如卟啉和醌）在该提议中具有显著的特征。 类似于重组能和反应的紧密耦合 自由能，据信激活的振动模式 在光合作用反应中吸收能量 中心在高效分离中发挥着核心作用， 在早期光合作用过程中，电子穿过细胞膜从空穴传来。 迄今为止完成的工作集中在利用光学泵浦相干 光学探测实验，以研究ET反应发生的速度比 溶剂的纵向弛豫时间。这样一个连贯控制的 ET反应最近被牵连在远程光合作用 电荷分离事件。除了我们设计的实验性努力之外， 培养对教育技术中连贯现象的基本理解 反应，其他工作利用光学泵浦红外探测实验来探测 容易识别的高频和低频之间的关系 发色团振动光谱标记（C-O和C-N伸缩模式， 芳烃和吡啶鎓环呼吸模式、卟啉皱褶模式等） 和ET反应坐标。如此详细的研究 振动耦合到ET都将提供一个新的水平， 了解生物电荷分离反应，并帮助 模拟光合作用的人工系统的设计， 影响新的能源存储技术。

Electron transfer (ET) is one of Nature's most important reactions, playing key roles in respiratory and photosynthetic pathways that are of fundamental bioenergetic significance. Though relatively well understood as a reaction class, ET reactions are not understood in detail in terms of the molecular features that define reactivity: ultrafast vibrational spectroscopy (infrared or coherent optical) will provide the first direct experimental probe that will help decipher how molecular motions are coupled to actual ET events. The reorganization energy (l),comprised of inner-sphere (high-frequency vibrational modes of the donor, acceptor, and medium) and outer-sphere (low-frequency vibrational modes of the solvent or bath) contributions, is of primary significance in determining how fast ET occurs in a given donor-acceptor system. Our goal to actually identify and measure the energy of vibrational modes that are key to an ET reaction coordinate represents an unexplored experimental frontier: the potential to add to our fundamental knowledge of charge transfer chemistry as well as influence the theoretical framework that has been developed to describe ET reactions is enormous. Our work focuses on simple donor-acceptor complexes that undergo fast charge separation and/or change recombination reactions (kET greater than 2 x 10[12] s-1); the requirement of fast ET ensures that vibrational dephasing of excited-state reactants as well as ground- and excited-state ET products does not occur on our experimental timescale. Model systems that allow pair-wise examination of reaction center-type chromophores (such as porphyrins and quinones) feature prominently in this proposal. Similar to the intimate coupling of reorganization energy and reaction free energy, it is believed that the vibrational modes that activate chromophores for ET and accept energy in the photosynthetic reaction center play a central role in the highly efficient separation of an electron from a hole across a membrane during early photosynthetic events. Work completed to date has concentrated on utilizing optical pump-coherent optical probe experiments to study ET reactions that occur faster than the longitudinal relaxation time of the solvent. Such a coherently controlled ET reaction has recently been implicated in the long-range photosynthetic charge separation event. In addition to our experimental efforts designed to develop a fundamental understanding of coherence phenomena in ET reactions, other work exploits optical pump-IR probe experiments to probe the relationship between the readily identifiable high and low frequency chromophore vibrational spectroscopic tags (C-O and C-N stretching modes, arene and pyridinium ring breathing modes, porphyrin ruffling modes, etc.) and the ET reaction coordinate. Such detailed studies of how molecular vibrations are coupled to ET will both provide a new level of understanding of biological charge separation reactions as well as aid in the design of artificial systems that mimic photosynthesis, potentially impacting new energy storage technologies.