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Synthetic Modifications and Solid State Structural Analysis of Bridged Molecular Gyroscopes and Solid State Photochemistry of Alkyl-Substituted α-Santonin

  • Author(s): Commins, Patrick John
  • Advisor(s): Garcia-Garibay, Miguel A
  • et al.

The field of solid state chemistry studies the reactivity and chemical transformations of solid phase materials. Although the tools used for analyzing the chemical properties and dynamics in solids have historically been rudimentary, one of the great advantages of studying solids is that all of the atoms are arranged in precise positions. Knowing this information can provide a great sense of control and understanding of the reaction environment present in solids. By analyzing compounds in the crystalline state, structural variations, such as functional group substitutions and deletions, can be rigorously monitored and their exact effect on the compound's solid state reactivity can be understood. To this extent, my work has focused on studying the effects of synthetic modification and solid state analysis towards two fields--crystalline molecular machines in the form of bridged molecular gyroscopes and solid state photochemistry by synthetically altering α-santonin.

Chapter one provides a brief introduction to the field of organic solid state chemistry, in which the fundamentals of both molecular machines and solid state photochemistry are discussed. The molecular machines overview reviews the first molecular machines and the advancement of molecular gyroscopes through the literature. The area of solid state photochemistry is also described, and its underlying principles such as the topochemical postulate, are examined.

Chapter two details a general strategy for synthesizing bridged molecular gyroscopes. A one-pot macrocyclic synthesis was developed and it was found to be robust in forming ether and ester linked macrocyclization. The results yielded both singly and triply bridged molecular gyroscopes and revealed the propensity for bridged molecular gyroscopes to "collapse" in toward the rotator, ultimately hindering the desired rotation.

Chapter three describes the design synthesis and solid state characterization of an azobenzene bridged molecular gyroscope that was made to function as a photochromic molecular brake. The compound was synthesized and its solid state physical characteristics were analyzed using UV-Vis absorption spectroscopy, single crystal X-ray diffraction and spin echo 2H NMR. The compound was found to undergo a photochromic isomerization between a cis and trans isomer as a nanocrystalline suspension and the energy of activation for the cis and trans states was measured to be 4.6 kcal/mol and 5.1 kcal/mol, respectively, indicating a 0.5 kcal/mol difference between the two states.

Chapter four explores the addition of different functional groups to the bridged molecular gyroscopes in order to understand and control the packing of the molecules. Two of the compounds were found to have isostructural packing and crystallized in the desired lamellar sheet arrangement. The data suggested that the electronic and steric environment shared between these functional groups was key in attaining the lamellar structure.

Chapter five was done in collaboration with the Naumov group at New York University in Abu Dhabi and describes the synthesis, crystal packing, and photochemical reactions of α-santonin and its methyl, ethyl, n-propyl, and n-butyl derivatives. The photosalient effect of α-santonin was captured, using a high-speed camera, and its splitting found to occur normally to the b axis of the unit cell. The study analyzed the crystal structures and the photochemistry both solution and using nanocrystalline suspensions in water. The solution photochemistry was in accord with literature precedence and the crystalline suspensions yielded a variety of photoproducts including a hydrate, which is not commonly observed in neutral water. An exocyclic alkene photoproduct was also discovered and its presence is hypothesized to be produced by an intermolecular deprotonation caused by a molecule of water present in the crystal.

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