Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Physics

Supervisor

Yang, Song

Abstract

Chemical transformations of molecular materials induced by high pressure and light radiation exhibit novel and intriguing aspects that have attracted much attention in recent years. Particularly, under the two stimuli, entire transformations of molecular species can be realized in condensed phases without employing additional chemical constraints, e.g., the need of solvents, catalysts or radical initiators. This new synthetic approach in chemistry therefore satisfies increasing need for production methods with reduced environmental impacts. Motivated by these promises, my Ph. D thesis focuses on this state-of-the-art branch of high-pressure photochemistry. Specifically, high pressure is employed to create the necessary reaction conditions to transform molecular materials, whereas monochromatic light is applied to trigger and direct the chemical reaction according to selective paths. Systematic studies on selective molecular hydrocarbon materials provide new insights into the understanding of different effects that is achieved by the combined pressure-light tuning and demonstrate significant feasibility and controllability of the method in material synthesis.

Using optical microscopy and vibrational spectroscopy, I firstly studied pressure effects on production of energetic materials from laser-induced decomposition of fluid ethylene glycol and mixture of 2-butyne and water. The work demonstrated that type of reactions and quantity of products as well as the associated kinetics were highly pressure dependent. Next, I examined pressure effects on photochemical phase transitions of fluid (Z)-stilbene. The study showed that increasing pressure not only tunes the photoisomerization type phase transitions but also opens a new reaction type, and thus allowing the production of novel crystal and liquid material, respectively. Finally, I explored polymeric transformations from three unsaturated hydrocarbon monomers under high pressure and/or UV radiation. In these studies, single reaction channel permits the quantitative analysis of polymerization kinetics and the pressure-dependence, so that correlations between rate constant, activation volume and pressure can be obtained. Moreover, physical states of matter accessed by compression significantly influence the polymerization kinetics, selectivity and microstructures of products. Overall, these studies provide important contributions in discovering and understanding the high-pressure photochemical behaviors of molecular materials and show profound implications of using the combined pressure photon tunable power to produce controlled molecular materials of potential new applications.

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