Development of synthetic methodologies toward five-membered S-heterocycles and their fluorinated derivatives: Applications to liquid crystal synthesis | Posted on:2003-06-09 | Degree:Ph.D | Type:Thesis | University:Kent State University | Candidate:Kiryanov, Andre Anatolievich | Full Text:PDF | GTID:2461390011984210 | Subject:Chemistry | Abstract/Summary: | | This dissertation describes the development of synthetic approaches toward a variety of novel liquid crystals containing five-membered S-heterocycles and their fluorinated derivatives. It was anticipated that these S-heterocycles would have several beneficial physical characteristics when compared to their phenyl counterparts, such as lower viscosity, fast switching times and high dielectric biaxiality, and might be useful in surface-stabilized ferroelectric liquid crystal (SSFLC) displays.; Chapter II deals with the synthesis of potential achiral host materials for SSFLC displays. A series of studies toward the synthesis of the liquid crystalline thienylbiphenyl and terphenyl compounds containing 1,1-difluoropentyl terminal chain are delineated, including fluorodeoxygenation (using DAST, MorphDAST and DeoxoFluor®) and fluorodesulfurization ([DBH, NBS, NIS or NOBF4]/Pyr-xHF) approaches. These 1,1-difluoropentyl-based systems displayed significantly different mesomorphic behavior from the other more conventional alkyl, alkoxy and alkanoyl-based compounds and were characterized by high melting points and a tendency toward orthogonal phase behavior (S A and SB phases). Only in a single case was a disordered tilted phase (SF) observed in such systems. A number of the analogous alkoxythienyl and alkylthienyl mesogens display remarkably high SC mesophase stabilities for ‘bent’ compounds and warrant further investigation as potential achiral ferroelectric host materials.; Chapters III and IV outline our progress toward chiral non-racemic S-heterocyclic ferroelectric dopants with low melting points and high dielectric biaxiality. Specifically, in Chapter III, the synthesis of several liquid crystals containing 5-alkoxy-1,3-thiazole and 2-alkyl-1,3,4-thiadiazole moieties via microwave-assisted Lawesson's reagent-mediated cyclization of the corresponding 1,4-dicarbonyl precursors is described. These liquid crystals were found to have high clearing points and supported the desired smectic C mesophases.; In Chapter IV, an effort was made to synthesize the fluorinated thiophene moiety via a Balz-Schiemann fluorination approach and introduce it into liquid crystalline materials using regioselective electrophilic bromination and regioselective Suzuki coupling chemistry. One of the target fluorinated mesogens supported tilted smectic C mesophases at substantially lower temperatures than those of the corresponding non-fluorinated derivative. A detailed study of the physical properties of this compound showed that this new material is of exceptional promise for the use in SSFLC displays and other applications. | Keywords/Search Tags: | Liquid, S-heterocycles, SSFLC, Fluorinated, Synthesis | | Related items |
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