Browsing by Subject "Heterocyclic compounds"
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Item Annulated bis(imidazolium) salts: synthesis, characterization, and applications(2007-12) Boydston, Andrew Jackson, 1978-; Bielawski, Christopher W.; Willson, C. G. (C. Grant), 1939-The design, synthesis, characterization, and applications of annulated bis(imidazolium) salts are described. New synthetic methodologies have been developed that allow access to a broad structural range of bis(imidazolium) salts. Initial studies focused on thee use of bis(imidazolium) salts as comonomers in the formation of mainchain organometallic polymers. Two distinct polymer scaffolds were synthesized, one featuring metal(II)dihalides in the main-chain, and the other featuring a chelated metal center. Ultimately, polymerizations were conducted under ambient atmosphere, proceeded in excellent overall yield, and provided main-chain organometallic polymers comprising Ni(II), Pd(II), and Pt(II) with molecular weights up to 106 Da. Departing polymer studies, focus was shifted toward the study of the physical and photophysical properties of the bis(imidazolium) salts. In few synthetic manipulations, a series of highly photoluminescent bis(imidazolium) salts were prepared whose substituents enable emission in solution, in the solid-state, and, uniquely, as free-flowing liquids. Importantly, these materials display excellent physical properties, such as low glass-transition temperatures (< 0 °C) and high thermal stabilities (> 300 °C). In addition, the bis(imidazolium) platform enabled access to two new fluorescent ionic liquid crystals, demonstrating an ability to also control mesomorphic properties of these materials. Further investigations were conducted regarding the photophysical properties of bis(imidazolium) salts. Focus was placed upon absorption and emission wavelength tunability, solvatochromism, red-edge excitation, and chemical stability. Through functional group modulation, the [lambda]em were varied from 329 -- 561 nm with [Phi]fs up to 0.91. Both the absorption and emission characteristics were found to display strong solventdependencies which were found to be strongly influenced by the nature of the bis(imidazolium) core. The red-edge effect was investigated for a series of bis(imidazolium) salts and was found to be similar between Br and BF4 salts, but distinctly different when MeSO4 anions were incorporated. The stability of an amphiphilic BBI was quantified in aqueous solutions of varying pH and > 85% of the emission intensity was retained after 2 h at pH levels of 3 -- 9.Item Development of new membranes based on aromatic polymers and heterocycles for fuel cells(2007-05) Fu, Yongzhu, 1977-; Manthiram, ArumugamProton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) have drawn much attention as alternative power sources for transportation, stationary, and portable applications. Nafion membrane is currently used in PEMFC and DMFC as electrolyte, but is confronted with a few difficulties: (i) high cost, (ii) limited operating temperature (< 100 o C), and (iii) high methanol permeability. With an aim to overcome some of the problems encountered with the Nafion membrane, this dissertation focuses on the design and development of new polymeric materials systems for use in PEMFC and/or DMFC. Sulfonated polysulfone (SPSf) membranes with various degrees of sulfonation were prepared and investigated in DMFC. With a degree of sulfonation of 50 - 70 %, the SPSf membranes exhibit low methanol permeability and electrochemical performance comparable to that of Nafion 115, making it an attractive low-cost alternative to Nafion. However, lower performance at higher current densities due to their low proton conductivities compared to Nafion is a disadvantage. It is found that the low methanol crossover is due to narrower hydrophilic channels, resulting in water/methanol confinement as in sulfonated poly(ether ether ketone) (SPEEK) membranes. Replacement of water by imidazole in Nafion helps to keep high proton conductivity at higher temperatures (> 100 o C) due to Grotthuss-type mechanism, but imidazole poisons the Pt catalyst. Interestingly, doping the Nafion-Imidazole composite membrane with H3PO4 partly suppresses the imidazole poisoning of the Pt catalyst. Employment of Pd-Co-Mo catalyst instead of Pt improves the fuel cell performance at 100 o C further due to a higher tolerance of the non-platinum Pd-Co-Mo catalyst to imidazole. Encouraged by this, benzimidazole group was then selected to promote proton conduction in the environment of sulfonic acid groups instead of imidazole (pKa = 7.0) due to its lower pKa value (5.5). Accordingly, 1,3-1H-dibenzimidazole-benzene containing two benzimidazole groups was synthesized and blended with SPSf. The blend exhibits higher proton conductivity under anhydrous conditions than plain SPSf and offers improved fuel cell performance and lower methanol crossover in DMFC. Polysulfones containing pendant N-heterocycles like benzimidazole, 2-amino-benzimidazole, or 3-amino-1,2,4-1H-triazole units were designed and synthesized. Blend membranes containing these polymers and SPEEK exhibit higher proton conductivities under anhydrous conditions as well as higher fuel cell performance due to acid-base interactions involving Grotthuss-type mechanism. They also lower methanol crossover further due to the insertion of the pendant N-heterocycles into the hydrophilic channels of SPEEK, improving the long-term stability in DMFC and reducing the Pt loading at the cathode side.Item Item Novel calixpyrrole-like anion receptors(2004) An, Deqiang; Sessler, Jonathan L.Calix[n]pyrroles (n ≥ 4) are venerable anion receptors that are based on single pyrroles and ketones as building blocks. However, the existence of only one variable, n, that defines the nature of the systems, limits this class of macrocycles to only a few core structures. To overcome this limitation, a series of building blocks other than single pyrroles, have been applied to the construction of novel calixpyrrole-like systems. These building blocks include bipyrrole, furan, thiophene, and 1,3-bispyrrolylbenzenes. Based on bipyrrole as the sole building block, a series of calix[n]bipyrroles (n = 3, 4) was synthesized. Based on bipyrrole, furan or thiophene as co-building blocks, calix[2]bipyrrole[m]furan[n]thiophene (m + n = 2) were obtained. Based on 1,3- bispyrrolylbenzenes, calix[n]bispyrrolylbenzenes (n = 2 - 4) were synthesized. These novel calixpyrrole-like macrocycles contain different core structures than calix[n]pyrroles, and thus display different anion binding properties than their parent systems. This, in turn, means that these new systems are not only helping to the chemistry of calixpyrroles, but also giving rise to selective receptors that find applications in anion coordination chemistry.Item Novel N-heterocyclic carbene architectures for use in carbene based polymers and redox swithcable : catalysis(2008-08) Kamplain, Justin Wade, 1980-; Bielawski, Christopher W.The central focus of this dissertation pertains to the synthesis and study of novel N-Heterocyclic carbene architectures. This pursuit has led to advances in carbine structure and bonding, and application of NHCs in materials chemistry in the role of monomer and catalystItem Novel N-heterocyclic carbenes: applications in materials chemistry and catalysis(2008-05) Khramov, Dimitri Mikhailovich, 1981-; Bielawski, Christopher W.A unifying theme of the chemistry presented is the synthesis, study, and application of a novel N-heterocyclic carbenes. Pursuit of these materials has resulted in new advances in carbene structure and bonding, the discovery of highly-efficient reactions, and the development of new polymers with unusual properties.Item Study of 10-methylphenothiazine cation radical chemistry.(Texas Tech University, 1975-08) Padilla, Amphlett GregNot available