2+2] photocycloadditions have been the basis of study for many years, due to numerous potential applications, for example: optical switches, shape-memory polymers, and photolithography. Even though these reactions have been widely studied, there are still unanswered questions. These cycloadditions in the solid state become more complicated due to the limited movement allowed by solids. Understanding the effect this limit has on the system is necessary for understanding the photoreaction. A

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... fic example is a single-crystal-to-singlecrystal (SC to SC) transformation. Generally, materials undergo a SC to SC reaction when irradiated with light in the tail of the absorption band ("tail" irradiations) or wavelength selective irradiations. The reaction progresses differently with broadband irradiations. There are very few materials that actually can undergo a single-crystal-to-single crystal photoreaction. Cinnamic acid is one of those few materials. Two materials, cinnamic acid and a supramolecular complex, 2(4, 4 bipyridyl ethylene) · 2(resorcinol), have been studied using tail irradiations. Partially-reacted single crystals of cinnamic acid have been examined, and the tensor of the product has been determined. Domain size experiments using spin diffusion have been performed for determining the mechanism of formation of the products under wavelength selective irradiation in cinnamic acid single crystals. The wavelength selective kinetics curve for the supramolecular complex has been determined. The crystal structure of the product has also been determined and confirmed with powder X-ray diffraction and simulations. The third material studied is a shape-memory polymer which was synthesized for the purpose of analyzing the photoreaction and the reversible crosslinking. The results of 13 C CP (cross polarization) and CPMAS solid state NMR experiments will be discussed. iii Acknowledgements As I write this I am reminded of all of the people who have helped me to be able to get this far. I would like to thank my committee, Dr. Jake Schaefer and Dr. Kevin Moeller for being there for me in my committee meetings, and for being willing and able to answer any and all questions that I had for you. Thank you for all of your help in my committee meetings helping to make sure that I stayed on track and for helping me to acknowledge the gaps in my knowledge. I would also like to thank my defense committee, Dr. Richard Mabbs, Dr. Viktor Gruev, and Dr. Mark Conradi for being willing to take the time out of their busy schedules to read my thesis and be a part of my defense. I would like to especially thank Dr. Mark Conradi for his help in the design and understanding of my probe. You are always a wealth of knowledge and I have always enjoyed our interactions. I would also like to thank our collaborators on these projects, Dr.