Studies of the Structural Boundaries of Solid-State Photodimerization Reactions via Isocoumarins and Heteromeric Assemblies

The study of molecules in crystals has gained considerable attention in the field of structural chemistry. Much interest has focused on the use of molecular crystals for the construction of materials with specific functional properties. Because the design of such materials requires a critical understanding of intermolecular interactions, use of the building-block approach continues to offer an important strategy to multimolecular frameworks. Though the use of template and metal-ligand interactions has provided successful opportunities to organize chemical reactions in solids, these methods require secondary molecules and are limited to achiral starting materials. As such, exploring chiral synthesis with simplified precursors holds much promise to the design of next generation materials. Recent research conducted in Dr. Wheeler's group focused on [2+2] photodimerization reactions of olefins by investigating a family of cinnamylsulfonamides that self-assemble to give photoreactive dimers. Though photodimerization in solids has been extensively studied, photobehavior of cocrystalline systems constructed from two chemically distinct molecules and chiral materials are rare.This thesis focuses on a cocrystalline approach for the construction of multicomponent assemblies to study solid-state [2+2] photodimerization reactions. Racemic alanine sulfonamidecinnamic acid (a fish hook shaped molecule) successfully cocrystallized with co-formers 4,4'-dipyridyl, 4,4'-dipyridyl-N,N'-dioxide dehydrate, and trans-1,2-bis(4-pyridyl)ethylene by use of the complementary features of hydrogen bonds and molecular shape to form supramolecular tetramers. The co-former (E)-but-2-enediamide did not result in cocrystal formation. Though cocrystals obtained from co-former trans-1,2-bis(4-pyridyl)ethylene effectively organized adjacent olefins for [2+2] photodimerization reaction via an inter-dimer route, UV illumination did not result in the cyclobutane photoproduct.In a second study, racemic and chiral syntheses of sulfonamide isocoumarin compounds and their [2+2] photodimerization reactions were examined. Two fish-hook shape molecules were synthesized by use of racemic and homochiral sulfonamide isocoumarin compounds. All synthetic steps were analyzed using NMR techniques, and where possible, X-ray crystallography. Racemic isocoumarin was crystallized by use of hydrogen bonds to form a supramolecular homodimer. These homodimers aligned with favorable olefin· · · olefin spacing for UV initiated single-crystal-to-single-crystal (SCSC) [2+2] photodimerization reactions to give cyclobutane photoproduct in 100% conversion. While homochiral isocoumarin could not be processed as a SCSC reaction, photoirradiation of a powdered sample gave cyclobutane photoproduct in 64.6% conversion as revealed by NMR studies.