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Engineering and Characterizing Dynamics in Crystalline Solids: Progress Towards Coupling Molecular Rotors via Mechanical or Electromagnetic Interactions

  • Author(s): Jellen, Marcus James
  • Advisor(s): Garcia-Garibay, Miguel A
  • et al.

The early investigations of Jean-Pierre Sauvage, Sir J. Fraser Stoddart and Bernard J. Feringa into artificial molecular machines (AMMs) were recognized with the 2016 Nobel prize for the development of molecules with controllable movements, allowing them to perform various tasks when provided with energy. The first examples of AMMs mimicked the function of macroscope machines such as molecular motors, molecular gyroscopes, and a variety of other simple machines. Synthesizing these structures required connecting multiple molecular components such as a stator, axle, and rotator to create autonomous structures. These final ensembles minimize the number degrees of freedoms accessible to their molecular components, allowing them carry out a specific function when given an appropriate stimulus.

A new paradigm in the field has recently emerged whereby chemists consider the collective function of many molecules in concert, rather than the function of an individual machine. For example, the combination of many molecules into a crystalline array creates materials with functionalities that are related to the physicochemical properties of each molecule, but the ensemble also has opportunities to exhibit high-order, emergent properties. When the molecular components contain magnetic or electric dipoles, domains in these materials have potential to respond in a cohesive manner when interfaced with external stimuli. The magnitude of this response allows a user to transduce various forms of energy, such as mechanical work to electricity, encode memory in magnetically polarized states or to store charge on the macroscopic scale. Applying the principles above to current technologies allows the creation of higher-order function systems and the development of advanced (programmable) materials. However, the precise control of microscopic motions through macroscopic inputs has not yet been achieved. My doctoral research focuses on using molecular rotation to develop both autonomous- and collective function-type molecular machines.

Chapter One is a perspective on strategies to develop crystalline molecular gears utilizing amphidynamic crystals. Chapter Two describes the synthesis and study of the first amphidynamic crystal containing a nitroxide-based paramagnetic rotor. Interestingly, a combination of SQUID magnetometry and EPR measurements revealed that this material has potential for developing ferromagnetic materials and has anisotropic interactions with impingent radiofrequency, demonstrating the potential of amphidynamic crystals to be utilized in quantum information science. Chapter Three is about the investigation of hydrogen bonded cocrystals containing molecular rotors and their ability to develop relaxor-type ferroelectric materials. Chapters Four establishes the importance of macrocyclization for enhancing gearing fidelity of molecular spur gears utilizing a previously known spur gear example combined with a convenient approach cyclize the compound with a gold-phosphine complex. Using molecular simulations, we were able to show that this compound is the most efficient spur gear synthesized to date. Chapter Five is a study about the dynamics and viscosity of solvents within nanoconfined environments. Using a combination of various NMR techniques, we were able to use the ligands of two amphidynamic MOFs to measure the viscosity of six different solvents at different temperature ranges. We also used a combination of T1, T2 and diffusion measurements to understand the various dynamic processes of the solvent molecules and teased out the barriers to various processes leading to motion within the MOF. Using these measurements, we attempt to make a model for the behavior of solvent molecules going from a static environment to an intermediate regime and finally to a highly dynamic environment.

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