Advances in Metal-organic Frameworks: From Engineered Photo-responsivity to Cutting-edge Characterization

The research described in this dissertation encompasses two areas of permanently porous crystalline materials; the design, synthesis, and characterization of photo-active metal-organic frameworks utilizing the diraylethene class of photochromes, and the characterization and analysis of flexible metal-organic frameworks and the factors contributing to change in lattice structure. The development of photo-responsive metal-organic frameworks was accomplished largely through the design and development of photochromic organic linkers. The developed linkers utilized a stable and rigid phenanthrene backbone with a photochromic diarylethene pendant group. The design of these ligands afforded the maximum potential inclusion of the photochromic moiety into the void space of the resulting metal-organic framework. The study of the resulting photo-active MOFs (UBMOF-1, -2, and -3) led to numerous insights into the effects of covalent incorporation on the photophysics of the linker, as well as the discovery of novel fatigue products in diarylethene based metal-organic frameworks. The insights gained into the incorporation of the diraylethene photochromic moiety into metal organic frameworks will aid in the future design of photo-responsive metal-organic frameworks. The in situ study of flexible metal-organic frameworks throughout the processes behind the change in lattice structure can lead to important insights into factors driving the flexibility of the lattice. A greater understanding of guest-host interactions and structural factors behind the flexibility in metal-organic frameworks is crucial to the design of more effective materials. The guest evacuation and loading process of the [Co(AIP)(Bipy)0.5(H2O)]•2H2O framework, and corresponding structural change, was studied through in situ single crystal X-ray diffraction. Through the use of an environmental control cell designed for single crystal studies, and the careful control of the environment of the sample, the dehydration process of the framework and associated structural changes were studied in detail. The stabilized congeners along the dehydration path offered insights into the role of guest-host interactions on the change in structure of the lattice. Further, the guest selectivity and loading process of the framework were studied through the selective loading of the evacuated framework with carbon dioxide. The response of the lattice to the guest and the apparent selectivity offered further insights into the role of guest-host interactions and structural components on the flexibility and shape of the lattice. Studies on the temperature dependent flexibility of a series of interpenetrated frameworks with a diamondoid net, X-dia (Co, Ni) series, throughout a wide temperature range provided insight into the role of structural components on the flexibility of the frameworks. The role of the metal center of the frameworks was investigated through the comparison of the structural response to temperature of the series of isostructural frameworks. Insights gained into the factors governing the flexibility of metal-organic frameworks offer valuable information for the design of future flexible materials.