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From Gold-Containing Liquid Crystals to Homodesmotic Reaction Analysis
AdvisorKing, Benjamin T.
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This dissertation describes, as a first part, the synthesis and characterization of gold-containing liquid crystals and poses a hypothesis for the charge carrier mobility of such liquid crystals. The second part describes pi-pi stacking as a non-covalent interaction through the use of computational methods. The third part illustrates electronic structures of certain systems, and a structural simulation of both a monomer and a polymer.Some gold-containing liquid crystals incorporate gold(I) as a linear linker and pyrazole as a chelating ligand. The resulting structure is a cyclic trimer known as a "metallatriangle." Liquid crystals of this nature tend to form columnar hexagonal mesophases due to the planar nature of the gold pyrazolate core giving rise to columnar order. Gold-gold interactions are often observed in certain cases of gold-containing complexes, and give rise to close gold-gold contacts. A gold-containing liquid crystal with close gold-gold contacts is expected to exhibit high charge carrier mobility and be readily processable. The fluid-like nature of the alkyl chains and the crystalline-like order resulting from pi-pi stacking and gold-gold interactions promotes self-healing of the material. We report on the synthesis of various gold-containing liquid crystals with one in particular satisfying our requirements: 1. Absorbs at 337 nm, which is the photoexcitation wavelength for our time of flight apparatus, 2. Is a room temperature liquid crystal, and 3. Is stable in its isotropic liquid state. Our time of flight measurements were unsuccessful so we strive to investigate the charge carrier mobility using an alternative method.pi-pi Stacking as a non-covalent interaction is described well through theoretical methods as evidenced by numerous studies found in the literature. However, accurate simulations of such systems are computationally expensive. Density functional theory is a computationally inexpensive method for the analysis of numerous molecular systems. Recently, non-covalent interactions are efficiently approximated using density functional theory. We describe the use of density functional theory and homodesmotic reaction equations to understand pi-pi stacking. We found that our results are in good agreement with computationally expensive methods, such as coupled-cluster calculations.Computational methods for the simulation of electronic structures may reveal important physical aspects of certain systems, including electron-donor or acceptor properties. Furthermore, periodic systems, such as polymers or crystalline materials, may be simulated to support empirical data and propose internal structure of systems that cannot be empirically measured. We found that, using density functional theory, the boronic ester moiety lowers the energy of frontier molecular orbitals for triphenylene-containing liquid crystals. In a separate investigation, we used molecular mechanics to simulate the structure of a monomeric monolayer and its corresponding polymer monolayer as they would appear at the air-water interface.