CAS: Toward Molecular Control of Cage Escape Yields in Bimolecular Photochemistry

在化学系化学结构、动力学机制B项目的支持下，查佩尔山的北卡罗来纳州大学化学系的Gerald Meyer教授和他的团队正在研究用可见光引发的化学反应，目的是提高这种转化的效率。在大多数情况下，目标是优化反应性，使得每个吸收的光子产生一个所需的产物。这项研究结果的下游应用可能包括太阳能转换以及高价值有机化合物的光合作用。该项目位于光化学和无机化学的界面，重点是电子转移反应，非常适合各级科学家的教育。迈耶研究团队致力于支持在科学中代表性不足的学生的培训。作为该项目的一部分，正在计划在研究三角区和北卡罗来纳州农村开展涉及K-12学生的外联活动。该项目旨在获得对光敏剂和猝灭剂之间的光引发电子转移的机理洞察，这将允许优化和预测量子产率的方法。重点将放在激发态电子转移和电荷重组内的'遇到复杂的'双分子氧化还原反应固有的。已知遭遇复合物内的电荷重组会显著降低大多数光化学反应的产率至远低于1的值，但这种行为的起源在很大程度上仍然未知。Gerald Meyer教授和他的团队提出了系统的电子转移研究，将利用老式的第二和第三行过渡金属光敏剂的电荷转移激发态，以及新兴的地球丰富的基于钴，铁，锆和铜的光敏剂。具有定制的电荷、大小和还原电位的电子供体和受体猝灭剂预计将提供对相遇复杂结构的洞察，这对于理解控制所需产物逃逸的因素是必要的，即，笼子逃脱的收益。要解决的一个基本问题是光敏剂和/或猝灭剂结构是否可以在分子水平上调节以影响相遇复合物，从而影响笼逃逸产率。 超分子组装将用于量化相遇复合物内非共价相互作用对电子转移和笼逃逸的影响。变温动力学测量提出了量化的电子耦合内的遭遇复杂的，并确定的绝热性的激发态电子转移反应。拟议的研究在本质上是基础性的，但预计将影响太阳能转换和有机光氧化还原催化中使用的方法。从长远来看，从这些研究中获得的见解有可能为光敏剂遭遇复合物的分子水平设计提供合理的手段，这些复合物能够有效地收集太阳光子，驱动电子转移反应，并释放所寻求的-该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查进行评估，被认为值得支持的搜索.

With support from the Chemical Structure, Dynamics & Mechanisms B Program of the Chemistry Division, Professor Gerald Meyer of the Department of Chemistry at the University of North Carolina at Chapel Hill and his team are studying chemical reactions that are initiated with visible light with the aim of improving the efficiency of such transformations. The goal in most cases is to optimize the reactivity such that each absorbed photon produces one desired product. Downstream applications of the findings from this research may include solar energy conversion, as well as the photosynthesis of high-value organic compounds. The project lies at the interface of photochemistry and inorganic chemistry, with a focus on electron transfer reactivity that is well suited to the education of scientists at all levels. The Meyer research team endeavors to support the training of students underrepresented in science. Outreach activities involving K-12 students in the Research Triangle and rural North Carolina are being planned as part of the project. This project seeks to obtain mechanistic insight into photo-initiated electron transfer between a photosensitizer and a quencher that will allow optimization and a means to predict quantum yield. Focus will be placed on excited state electron transfer and charge recombination within the ‘encounter complex’ inherent to bimolecular redox reactions. Charge recombination within the encounter complex is known to significantly lower the yield of most photochemical reactions to values far below one, yet the origin(s) of such behavior remain largely unknown. Professor Gerald Meyer and his team propose systematic electron transfer studies that will exploit the charge-transfer excited states of vintage second- and third-row transition metal photosensitizers, as well as emerging earth abundant photosensitizers-based on cobalt, iron, zirconium, and copper. Electron donor and acceptor quenchers with tailored charge, size, and reduction potentials are expected to provide the insight into encounter complex structure that is necessary to understand the factors that control escape of desired products, i.e., the cage escape yield. A fundamental question to be addressed is whether the photosensitizer and/or the quencher structure can be tuned at the molecular level to impact the encounter complex and thereby the cage escape yield. Supramolecular assembly will be used to quantify the impact of non-covalent interactions within the encounter complex on electron transfer and cage escape. Variable temperature kinetic measurements are proposed to quantify the electronic coupling within the encounter complex and to determine the adiabaticity of the excited state electron transfer reaction. The proposed research is fundamental in nature yet are expected to impact approaches used in solar energy conversion and organic photoredox catalysis. In the long term, insights gained from these studies have the potential to provide a rational means for the molecular-level design of photosensitizer encounter complexes capable of efficiently harvesting solar photons, driving electron transfer reactions, and releasing the sought-after products.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.