Theoretical and Experimental Investigations of Photoheterolysis Reactions

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With this award, the Chemical Structure Dynamics and Mechanisms-B program is supporting fundamental research in the field of photochemistry, carried out by Arthur Winter at Iowa State University. The absorption of light by molecules can lead to cleavage of chemical bonds but it is often difficult to understand why or how specific bonds break. Dr. Winter and his students seek to understand the structure-reactivity principles for one general type of bond cleavage, specifically photochemical heterolysis of bonds between carbon and a leaving group. Heterolysis represents one of the possible ways in which a chemical bond can break, with both of the two electrons in the bond being given to one of the departing groups. Photoheterolysis reactions are important in biology, materials science and environmental chemistry. The long-term goal in this project is to create a predictive theoretical framework, which can relate chemical structure to excited state reactivity, thereby providing new guiding mechanistic principles that direct photochemical reactions. Among broader impacts activities, 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 also continue to recruit undergraduates and students from underrepresented groups into his lab. To study these photoheterolysis reactions, the PI will employ a combined theoretical/experimental approach. High-level computational methods will be used to map excited state transition states and surface crossing topologies in model systems. Experimentally, spectroscopy will determine the effect of structure on the rates and mechanisms of photorelease in model systems. In particular, ultrafast femtosecond-resolved transient absorption spectroscopy will be used to determine the rates and mechanisms of photoheterolysis reactions on selected substrates, while high-level excited state calculations will be used to provide a mechanistic rationale. This research will provide a broad range of training for undergraduate and graduate students.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.