CAS: Proton-Coupled Electron Transfer Reactions from Ligand-to-Metal Charge Transfer Excited States.

WIth support from the Chemical Structure, Dynamics & Mechanisms-B (CSDM-B) Program of the Chemistry Division, Professor Jillian Dempsey of the Department of Chemistry at University of North Carolina at Chapel Hill is studying new strategies for driving fuel and chemical production with light. The goal of the project is to establish light-activated reactions that form transition metal hydride complexes. Many of the catalytic processes by which fuels and commodity chemicals are produced proceed through transition metal hydride complexes. Therefore, routes to synthesize transition metal hydrides with light provide a sustainable route for fuel and chemical synthesis. The research activities will contribute to the development of a globally competitive science and technology workforce as trainees will develop skills in chemical synthesis and spectroscopy. Complementary activities led by Professor Dempsey aim to broaden participation of historically marginalized communities in science and to train a globally competitive workforce. Professor Dempsey leads the Chemistry Women Mentorship Network, which connects graduate students and postdoc women interested in academic careers with faculty mentors and designs resources to support successful mentor-mentee relationships. Professor Dempsey also leads a three-day workshop that provides hands-on training in both theoretical and practical aspects of electrochemistry to researchers around the country. The generation of transition metal hydride complexes using light would enable approaches that employ solar energy to drive these important, energy-intensive reactions. The excited-state proton-coupled electron transfer reactivity of transition metal complexes with ligand-to-metal charge transfer excited states has not yet been established, but is a promising strategy for integrating light capture and proton-electron reactivity. Under this award, foundational studies of coordination complexes with ligand-to-metal charge transfer excited states that combine synthesis, spectroscopy, and theory will be undertaken to establish the electronic structure factors necessary for low energy ligand-to-metal charge transfer transitions. Subsequently, photochemistry accessible from ligand-to-metal charge transfer excited states will be investigated, with a focus on demonstrating the scope of excited-state electron and proton transfer reactions accessible. Structure-function relationships and time-resolved spectroscopy will be instrumental in gaining new insight to photochemistry from these excited states. This knowledge will guide the investigation of unprecedented proton-coupled electron transfer reactions from complexes with ligand-to-metal charge transfer excited states. Spectroscopy and theory will provide key insight to the electronic structure properties that engender proton-coupled electron transfer reactivity. If successful, these studies will establish new strategies for integrating light capture and proton-electron reactivity. 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.