Theoretical and Experimental Investigation of Photoheterolysis Reactions

在化学系化学结构动力学和机制B计划的支持下，州立大学爱荷华州的亚瑟温特教授正在努力揭示碳离去基团（C-LG）键的光异裂解反应的结构-反应性原理。 这个项目的长期目标是产生一个预测性的理论框架，将化学结构与激发态的反应性联系起来，用于异裂键断裂。异裂键断裂代表化学键断裂的两种可能方式之一，其中键中的两个电子都被给予键中的一个原子。 这项工作的重点是研究这种键断裂如何发生时，分子被照射。 光异裂解反应在生物、材料和环境化学应用中是重要的。理解一个简单的原型键断裂光反应的机械原理将有助于理解指导光化学反应的指导机械原理的更广泛的问题。 温特教授还将参与一项新生研究计划，该计划涉及一年级大学生的早期多学科研究经验。他将继续从代表性不足的群体中招募本科生和学生进入他的实验室。在这个奖项下，Winter教授和他的团队寻求从激发态势垒和锥形交叉点的静态计算向前推进，并走向动态激发态轨迹。非绝热轨迹从初始光吸收事件开始开始，在激发态表面上演化，并跳跃到基态离子对光产物。这些模拟和实验将回答关键问题，包括：（一）是由过渡态控制或生产性的锥形交叉点（CI的）附近的离子对的存在下，光异裂解反应;（二）是否适用于S1和T1的哈蒙德假设，因为它不为热（S0）SN1反应？(iii)CI和CI接缝的地形如何影响漏斗处光异裂解反应的分支比？(iv)对于理解非绝热表面穿越的机制，CI的最小能量交叉点和周围的拓扑结构有多重要？(iv)自旋态和溶剂如何改变该机制？ 高水平的激发态轨道模拟与超快激光闪光光解实验相结合，将共同为回答这些具有广泛光化学相关性的迷人问题提供强有力的方法。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标准进行评估，被认为值得支持。

With the support of the Chemical Structure Dynamics and Mechanisms-B Program in the Division of Chemistry, Professor Arthur Winter at Iowa State University is working to uncover structure-reactivity principles for photoheterolysis reactions of carbon-leaving group (C-LG) bonds. The long term goal of this project is to generate a predictive theoretical framework that relates chemical structure to reactivity in the excited state for heterolytic bond scission. Heterolytic bond cleavage represents one of the two possible ways in which a chemical bond can break, with both of the two electrons in the bond being given to one of the atoms in the bond. This work is focused on studying how this bond breaking can occur when a molecule is irradiated. Photoheterolysis reactions are important in biological, materials, and environmental chemistry applications. Understanding the mechanistic principles for a simple archetypal bond-breaking photoreaction will contribute to the broader problem of understanding the guiding mechanistic principles that direct photochemical reactions. Professor Winter will also be involved with a Freshman Research Initiative that involves first-year college students in an early multidisciplinary research experience. He will continue to recruit undergraduates and students from underrepresented groups into his lab. Under this award, Professor Winter and his team seek to advance from static computations of excited state barriers and conical intersections and move toward dynamic excited state trajectories. Non-adiabatic trajectories begin from the initial light absorption event, evolve on the excited state surface, and hop to the ground state ion pair photoproduct. These simulations and experiments will answer key questions, including: (i) Are photoheterolysis reactions governed by transition state control or by the presence of productive conical intersections (CI’s) near the ion pair; (ii) Does the Hammond postulate apply for S1 and T1 as it does for thermal (S0) SN1 reactions? (iii) How does the topography of the CI and the CI seam influence the branching ratios of photoheterolysis reactions at funnels? (iv) How important is the minimum energy crossing point, and the surrounding topology, of the CI for understanding the mechanisms of non-adiabatic surface crossings? (iv) How does spin state and solvent alter the mechanism? High level, excited state trajectory simulations in combination with ultrafast laser flash photolysis experiments will jointly provide a powerful approach for answering these fascinating questions of broad photochemical relevance.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.