Photochemistry, photo retro diels alder reactions, photoacid, pentacene, polymers, materials
In chapter I Photo-retro-Diels-Alder (PrDA) reactions of a variety of Diels Alder (DA) adducts were studied. Experimental results showed that the photoreactivity (quantum yield) depends on the electron-donating ability of the diene component and the electronwithdrawing ability of the dienophile component. The mechanism was studied by trapping the reaction intermediate, O2 quenching and femtosecond time-resolved absorption spectroscopy. All the results support a mechanism that involves a charge-separated intermediate generated from a singlet excited state. The PrDA reaction may find applications in photoresponsive materials, photolithography, drug delivery and mechanistic research. Chapter II shows two applications of the PrDA reaction. The first, being the formation of the 2 nd -ring DA adduct together with the central-ring adduct in a reaction of pentacene and tetracyanoethylene (TCNE) at room temperature. DFT calculations showed that the difference between the free energy of the two isomers is about 3.9 kcal/mol. Photo- and thermally induced isomerization between the central-ring adduct and the 2nd -ring adduct were studied in solutions and in polymer films. In solution, the less stable 2nd -ring adduct can be completely converted to the more stable central-ring adduct either thermally or photochemically, but the reverse transformation does not occur. In a polymer matrix, isomerization can be photochemically induced in both directions at different wavelengths, which results in a photoswitchable system. Formation of pentacene in the photochemical experiments was also observed, which supports an isomerization process involving a photoretro-Diels Alder (PrDA) reaction. iv The second application was the design and synthesis of a polymer with an anthracene diketone moeity which could undergo a PrDA reaction which should result in significant conductivity changes. Although the synthesis of this type of polymer was unsuccessful during this study, we still believe in the theoretical soundness of the synthesis and utility of this type of polymer. Chapter IV undertakes the study of a class of photoacids which are based on a merocyanine core. These photoacids have been studied and characterized using UV-Vis spectroscopy and the pH of two photoacids have been shown to decrease by 2.0 units upon irradiation with blue light. In addition, the relaxation times of these photoacids have been studied in water and ethanol. We have taken one step further and synthesized and characterized three polymers which have a photoacid moeity in them. These polymers respond to visible light reversibly in solution and in solid state.
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Doctor of Philosophy (Ph.D.)
College of Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Dissertations, Academic -- Sciences, Sciences -- Dissertations, Academic
Johns, Valentine, "Photochemistry And Applications Of Diels-alder Adducts And Photoacids In Materials Science" (2012). Electronic Theses and Dissertations, 2004-2019. 2496.