Experimental Studies of Electron Tunneling Through Non-Covalent Contacts in Supermolecules

美国国家科学基金会的有机和高分子化学项目支持大卫H.沃尔德克和克里斯蒂安E. Schafmeister在匹兹堡大学的一个项目，该项目将研究化学反应物和溶剂的核波动（核运动）如何影响电子在远距离反应中的运动（大于或等于电子供体和电子受体之间的一个分子）。虽然当电子的运动或原子核的运动是速率控制时，对电子转移的理解已经很好地发展，但是中间的情况，其中电子运动和原子核运动都很重要，却没有实验研究。该项目将使用时间分辨荧光光谱和荧光相关光谱来跟踪定义明确的超分子中的电子转移，这些超分子旨在将电子供体和电子受体单元彼此并置一定距离，以便溶剂分子可以占据中间空间（“间隙”）。早期工作的一个重要延伸是创造和研究可溶于水的超分子。这一特性将允许研究电子隧穿水分子。第二个目标是了解溶剂摩擦和反应伙伴之间的电子相互作用（电子耦合）的强度如何影响反应速率。这里研究的模型系统可以有自己的属性（距离，电子耦合等）调整，使理论模型的功能可以探测。通过在水和水溶液中进行研究，研究与生物学和电化学系统相关的条件。本项目将发展对化学和生物学许多领域重要的超分子结构中的电子运动和遇到反应物复合物的理解和控制。例如，电子隧穿水分子的效率对于重要的生物能量过程的机械理解至关重要。这项工作的结果将通过科学会议和出版物传播。研究生和本科生的培训和教育是完成这项研究工作的主要机制。学生将获得现代激光方法，光谱学和纳米技术的专业知识，并学习如何设计测试理论模型的实验，以扩展我们的科学理解。一个特别的努力，以吸引学生从代表性不足的群体在化学研究将追求在各级：研究生，本科和高中（通过PECAP投资现在计划在匹兹堡大学和ACS种子计划）。

The Organic and Macromolecular Chemistry Program at the National Science Foundation supports Professors David H. Waldeck and Christian E. Schafmeister at the University of Pittsburgh for a project that will investigate how nuclear fluctuations of chemical reactants and solvent (nuclear motion) effect the electron's motion in reactions that occur over large distances (greater than or equal to one molecule intervening between the electron donor and electron acceptor). While the understanding of electron transfer is well developed when either the electron's movement or the nuclei's movement is rate controlling, the intermediate case, in which both electron motion and nuclear motion are important, has eluded experimental study. This project will use time-resolved fluorescence spectroscopy and fluorescence correlation spectroscopy to follow the electron transfer in well-defined supermolecules that are designed to juxtapose electron donating and electron accepting units at some distance from each other so that solvent molecule(s) can occupy the intervening space ('gap'). An important extension from earlier work is the creation and study of supermolecules that are soluble in water. This feature will allow the study of electron tunneling through water molecules. A second goal is to understand how the solvent friction and the strength of electronic interaction between the reaction's partners (electronic coupling) affect the reaction rates. The model systems studied here can have their properties (distance, electronic coupling, etc) tuned so that features of theoretical models can be probed. By performing studies in water and aqueous solutions, the conditions relevant to those in biological and electrochemical systems will be studied.This project will develop the understanding and control of electron motion in supramolecular structures and encounter complexes of reactants, which is important in many areas of chemistry and biology. For example, the efficiency of electron tunneling through water molecules is essential to a mechanistic understanding of important bioenergetic processes. The results of this work will be communicated through scientific conferences and publications. The training and education of graduate and undergraduate students is the primary mechanism through which this research work will be accomplished. The students will gain expertise in modern laser methods, spectroscopy, and nanotechnology, and learn how to design experiments that test theoretical models as a method to extend our scientific understanding. A special effort to attract students from under-represented groups in chemical research will be pursued at all levels: graduate, undergraduate, and high school (via the PECAP-Investing Now program at the University of Pittsburgh and the ACS Seed Program).