Molecular-engineered hybrid organic-inorganic functional materials and progress toward light-triggered expansive organic polymers

This dissertation describes research projects on the synthesis and characterization of hybrid organic-inorganic functional materials and organic photoexpansive polymers. After an introduction of hybrid organic-inorganic materials in Chapter 1, Chapters 2 and 3 describe the preparation, fabrication and application to bridged polysilsesquioxanes. The concluding Chapter 4 focuses on the design and development of photoexpansive organic polymers.; Chapter 1 gives a general introduction of hybrid materials, followed by a brief discussion of sol-gel chemistry since it plays a key role in the preparation of hybrid materials. Much of this chapter focuses on an overview of a new family of hybrid organic-inorganic materials that are prepared by sol-gel chemistry, namely bridged polysilsesquioxanes.; In Chapter 2, the preparation of integrated chemical systems that contain iron oxide and organo silsesquioxanes is described. The synthetic procedures we have developed allow the simultaneous formation of iron oxide and bridged polysilsesquioxane networks in monolithic xerogels and aerogels. The porosity and microstructure of the materials have been determined by nitrogen porosimetry, electron microscopy, and ultra small-angle X-ray scattering. These hybrid materials exhibit a uniform dispersion of both components with no evidence for phase separation at length scales >5 nm.; Chapter 3 reports the preparation of functionalized coumarin dimers and their application as photoresponsive building blocks. In this chapter, I first describe the synthesis and chemical elaboration of 7-substitued coumarin dimers, and evaluate the chemical stability, photochemical behavior and the use of these photodimers for material synthesis. I then focus our attention on the sol-gel derived coumarin-dimer bridged polysilsesquioxanes as photoresponsive hybrid materials, their fabrication as spherical nanoparticles and their evaluation as photopatternable thin films.; Chapter 4 describes the progress toward design and development of photoexpansive organic polymers. Several generations of polymer design are illustrated. The designed polymers contain photosensitive macrocycles in the backbone. These polymers are expected to expand and/or elongate upon photoirradiation but will not change molecular weight. Model systems were prepared by ring-opening addition to a macrocyclic dilatone. Their subsequent photochemistry was studied. The preliminary results revealed that the cyclobutane ring in the model systems can be photocleaved to the corresponding olefin. Several key precursors were synthesized, and ongoing efforts for polymer preparation are described.