CAS-Climate: Supramolecular Control of Reactivity in the Solid State: From Metal-Free Photoswitches and Click Reactivity to Manufacturing Diverse Molecules

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Nontechnical Abstract: This project, with support from the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, aims to advance the understanding of, and enhance the value of, reactions performed in the organic solid state. These new insights benefits materials researchers and synthetic chemists alike. Reactions performed in organic solids are relevant to the field of green chemistry: they are highly selective, high-yielding, and solvent-free. Reactions performed in organic solids can also be used to store chemical energy, which makes the solids valuable to develop materials for applications in sustainability. The potential of the organic solid state to be used as a medium to perform synthetic chemistry and develop sustainable materials, however, has been severely hampered by a lack of a general method to orient reactive groups into the proper geometry to undergo a chemical reaction. Professor MacGillivray and his research group make use of noncovalent bonds (e.g. hydrogen bonds) in a general way to guide the assembly of molecules in crystals so that reactive groups are properly and reliably aligned to undergo reaction. Thereby they study the scope of starting materials that react in the solid state and how to eventually manufacture a wide variety of molecules and materials as products. The research has the potential to lay the foundation for a “greener” manufacturing approach for the chemical industry where reactions can be performed using purely organic solids without the use of metals or metal ions. As part of the project’s outreach activities, high-school students are introduced to noncovalent bonding and organic solid-state chemistry. The principal investigator also involves students from underrepresented groups in the research activities, maintains active collaborations with undergraduate colleges, and engages middle-school students to promote careers in chemical science (e.g. X-ray crystallography). Technical Abstract: The project, supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, makes reactions performed in the organic solid state more valuable to synthetic chemists and materials scientists by developing solids that form the basis of functional materials and expand the scope of reactions and products. Specifically, the researchers study (i) their potential as metal-free organic switches, (ii) uses of cocrystals to perform metal-free ‘click’ reactions, and (iii) an approach to generate broad ranges of molecules. Photochromic switches are designed using hydrogen-bond-directed self-assembly that direct intermolecular [2+2] photodimerizations. The click reactions are conducted with the assistance of perfluorophenyl-phenyl interactions to generate extended pi-conjugated molecules. Broad ranges of molecules are synthesized in crystals using post-synthetic modifications of cyclobutanes functionalized with aryl nitriles. The research is motivated by the fact that although the organic solid state is a highly attractive medium to perform chemical reactions to make (and break) covalent bonds, there remains a lack of general methodologies to perform reactions ‘at will’ akin to the liquid phase. Outcomes of this research are expected to enable a broader application of reactions in solids to problems and challenges of organic synthesis (e.g. complex molecules, additional chemical reactions), green chemistry (e.g. solvent-free preparation), and materials science (e.g. single-crystal switches).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.