CAS: Assessing the Applicability of Marcus Theory to Excited-state Proton Transfer and Protonic Photochemical Energy Conversion

在这个由化学部化学结构、动力学和机理B项目资助的项目中，加州大学欧文分校化学系的Shane Ardo教授正在开发一系列具有专门设计的质子供体和质子受体基团的光酸和光碱分子。本研究的目的是利用这些分子来评估与激发态质子转移相关的速率常数的驱动力依赖性，这对太阳能利用很重要。该项目位于有机化学和光物理化学的界面，因此非常适合各级科学家的教育。这个群体也处于有利地位，可以为科学领域代表性不足的学生提供最高水平的教育和培训。与中学生开展外展活动，提高他们对STEM（科学、技术、工程和数学）的兴趣，培养对科学家和科学的信任，也将是资助项目的一部分。光酸和光碱是一种分子，其酸度在吸收光后发生可逆的变化。这可以导致激发态质子转移，用众所周知的Förster循环分析来描述能量学。最近，Shane Ardo教授和他的团队表明，许多由于动力学限制而不能经历激发态质子转移的光酸和光碱可以通过引入质子受体和/或质子供体缓冲物质来重新设计以克服这一障碍。这使得研究小组能够准确地预测激发态酸度，从而预测质子转移的标准态驱动力。在这个项目中，他们的目标是验证他们的新方法，然后用它来量化质子转移反应的标准态驱动力和激活自由能之间的关系，包括在马库斯倒转区。他们还旨在利用这一基本认识来设计和演示光化学质子能量转换系统，该系统使用光来调节两种缓冲物质的质子化状态。他们试图回答以下关键问题：1)电子转移和质子转移动力学的驱动力依赖理论，如Rehm-Weller， Marcus-Cohen, Agmon-Levine，是否适合描述激发态质子转移反应？2)能否调整光酸/光碱的基态酸碱度，使缓冲液和/或质子溶剂作为质子供体/受体，使光酸/光碱的基态共轭碱/酸再生？该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In this project, funded by the Chemical Structure, Dynamics & Mechanism B Program of the Chemistry Division, Professor Shane Ardo of the Department of Chemistry at the University of California-Irvine is developing a series of photo-acid and photo-base molecules with specifically designed proton donor and proton acceptor groups. The goal of this research is to use these molecules to evaluate the driving-force dependence for rate constants associated with excited-state proton transfer, which is important for solar energy utilization. The project lies at the interface of organic and photophysical chemistry, and is therefore well suited to the education of scientists at all levels. This group is also well-positioned to provide the highest level of education and training for students underrepresented in science. Outreach activities with middle school students that promote interest in STEM (science, technology, engineering and mathematics) and foster trust in scientists and science will also be part of the funded project.Photo-acids and photo-bases are molecules whose acidity changes reversibly upon absorption of light. This can result in excited-state proton transfer, with energetics described using the well-known Förster cycle analysis. Recently, Professor Shane Ardo and his group showed that many photo-acids and photo-bases that do not undergo excited state proton transfer due to kinetic limitations can be re-engineered to overcome this barrier through the introduction of proton acceptor and/or proton donor buffer species. This allowed the research team to accurately predict excited state acidity, and thus standard state driving force, for proton transfer. In this project, they aim to validate their new method and then use it to quantify the relationship between standard-state driving force and activation free energy for proton-transfer reactions, including in the Marcus inverted region. They also aim to leverage this fundamental understanding to design and demonstrate photochemical protonic energy conversion systems that use light to modulate the protonation state of two buffer species. They attempt to answer the following critical questions: 1) Are driving-force-dependent theories for the kinetics of electron transfer and proton transfer, e.g. Rehm–Weller, Marcus–Cohen, Agmon–Levine, suitable to describe excited-state proton transfer reactions? 2) Can the ground-state acidity/basicity of photo-acids/photo-bases be tuned so that buffers and/or protic solvents serve as proton donors/acceptors for regeneration of the ground-state conjugate base/acid of photo-acids/photo-bases?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.