CAREER: CAS: Organic Photochemistry for Light-Driven CO2 Capture and Release

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With support from the Chemical Structure, Dynamics & Mechanisms-B (CSDM-B) Program of the Chemistry Division, Richard Liu of the Department of Chemistry and Chemical Biology at Harvard University is developing new classes of photoswitchable organic compounds to enable control of carbon dioxide (CO2) binding and release with visible light. This fundamental knowledge may be used to develop devices that harness energy from sunlight to separate CO2 from emission streams or directly from the atmosphere and then release that captured CO2 on demand for utilization or storage. This project integrates these research goals with educational activities intended to promote broader participation in scientific careers, specifically aimed at engaging K-12 students in the Boston area as well as adult and non-traditional learners. Tools for teaching organic chemistry concepts to blind and low-vision students will also be developed, focusing on topics such as molecular geometry, stereochemistry, and isomerization reactions related to the research aims.Photochromic organic molecules are promising materials for directly light-driven separations, as they may be efficiently switched between two or more isomeric forms that can differ significantly in their chemical properties. The proposed research outlines general schemes for coupling of these optically controlled equilibria to downstream light-independent equilibria involving CO2 uptake into solution. In one mode, new compounds that enter a metastable, highly acidic state upon irradiation will be used for passive capture and on-demand release of CO2. In a second, complementary mode, reversible photobases – a neglected class of compounds with few known examples – will be employed to enable light-triggered capture and gradual passive release. Co-operative mechanisms involving the combination of photoacids or photobases with traditional amine sorbents will also be explored. For each class of compounds, in situ spectrophotometry, pH and CO2 measurement, and ultrafast spectroscopy will be used to characterize key photochemical mechanisms. The thermodynamic requirements for effective photoswitching will be revealed through systematic synthesis and evaluation of photoswitches.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.