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

美国国家科学基金会的有机和大分子化学项目支持匹兹堡大学的David H. Waldeck和Christian E. Schafmeister教授的一个项目，该项目将研究化学反应物和溶剂的核波动（核运动）如何影响远距离（电子供体和电子受体之间大于或等于一个分子）反应中的电子运动。当电子的运动或原子核的运动都是速率控制时，对电子转移的理解已经很好地发展了，但电子运动和原子核运动都很重要的中间情况还没有进行实验研究。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，这些超分子被设计成将电子给体和电子接受体并置在彼此之间一定距离的地方，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。这一特性将使电子在水分子中隧穿的研究成为可能。第二个目标是了解溶剂摩擦和反应伙伴之间电子相互作用的强度（电子耦合）如何影响反应速率。这里研究的模型系统可以调整其属性（距离，电子耦合等），以便可以探索理论模型的特征。通过在水和水溶液中进行研究，将研究与生物和电化学系统相关的条件。本项目将发展对超分子结构和反应物偶遇配合物中电子运动的理解和控制，这在化学和生物学的许多领域具有重要意义。例如，电子在水分子中隧穿的效率对于重要生物能量过程的机理理解是必不可少的。这项工作的结果将通过科学会议和出版物进行交流。研究生和本科生的培养和教育是本研究工作完成的主要机制。学生将获得现代激光方法、光谱学和纳米技术方面的专业知识，并学习如何设计实验来测试理论模型，作为扩展我们科学理解的一种方法。在化学研究领域，将在研究生、本科生和高中（通过匹兹堡大学的PECAP-Investing Now项目和ACS Seed项目）等各个层次上，特别努力吸引代表性不足群体的学生。

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).