Applications of supramolecular chemistry : synthesis of vinyl crown ethers, pharmaceutical polymorph control, diene photoreactivity, and thermal expansion in stoichiometric polymorphs
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Crystal engineering strategies have been applied to the design and synthesis of functional molecular solids with desired physical and chemical properties through reliable intermolecular interactions, including hydrogen bonding, ionic bonding, and π···π stacking. A convenient, high-yielding, and scalable synthetic approach to the construction of 4'-vinylbenzocrown ethers has been developed using a decarboxylation and cyclization strategy. The structures of the crown ethers were further confirmed via single-crystal X-ray diffraction studies. Two hydrates and one anhydrous form of the vinylbenzocrown ethers were crystallized using crystal engineering principles. We utilize cocrystallization/salification strategies to obtain salts of trimethoprim with enantiopure D- or L-lactic acid, with up to five times improved solubility. Both salts are polymorphic, and fully reversible interconversion (cycling) between their polymorphs is demonstrated via mechanochemistry and slurry methods. We demonstrate that polymorph interconversion requires both solvent contact and mechanical force, providing insights into the mechanism of cycling between solid forms. This thesis also investigates solid-state [2 + 2] photocycloadditions of dienes. By tuning the relative π-π stacking arrangement, we obtained two photoreactive crystals: an “out-of-phase” and an “in-phase” polymorph. A wavelength-selective light screening strategy was employed to systematically explore their photoreactivity. Under different wavelengths of light, the chemical functionality can be programmed into discrete and distinct products containing dimers, trimers, tetramers, or oligomers/polymers. Moreover, the wavelength-dependent photomechanical behaviors of these two polymorphic crystals were examined. Lastly, cocrystallization strategies were utilized to construct hydrogen-bonded binary solids with four stoichiometric polymorphs and one ternary solid. Thermal expansion behavior of these solids can be precisely controlled by systematically modulating the hydrogen bonding connectivity.
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Ph. D