Dissertation/Thesis Abstract

Preparation of Heteroatom-Substituted 1,3 Thiazoles as Building Blocks for Liquid Crystal Synthesis
by Grubb, Alan M., Ph.D., Kent State University, 2011, 314; 10631080
Abstract (Summary)

Ferroelectric liquid crystals (FLCs) offer several advantages for display applications, such as high resolution and fast switching speeds. However, chevron defects have commonly been observed in FLCs which have hindered their use in displays. In this dissertation, we present synthetic routes to four novel series of 2 alkoxy-, 5-alkoxy-, 5-alkoxy-4-fluoro, and 5-carboxy-1,3-thiazole-based FLCs (compounds 4.12, 2.12, 5.76, and 6.8, respectively), all of which showed smectic C* phases and three of which were free of chevron defects. The first series of FLCs presented (compounds 2.12) utilized a Lawesson's reagent-mediated cyclization of a corresponding α-benzamido ester to generate the first reported family of 5-alkoxy-1,3-thiazole-based liquid crystals in excellent yield. To facilitate efficient approaches to other alkoxy-substituted 1,3-thiazole-based FLCs, we developed new and improved preparations of two important synthetic building blocks, 2,4- and 2,5-dibromo-1,3-thiazole (compounds 3.11 and 3.3, respectively). These approaches offer significant improvements over the previously reported literature approaches. A second series of FLCs (compounds 4.12) was generated in excellent yield via selective SNAr chemistry on 2,5-dibromo-1,3-thiazole (3.3) to produce the first reported family of 2-alkoxy-1,3-thiazole-based liquid crystals, which are structural analogs of the previously presented 5-alkoxy-1,3-thiazole-based FLCs. In a third study, electrophilic aromatic fluorination was used to generate the first reported series of 5-alkoxy-4-fluoro-1,3-thiazole-based FLCs (compounds 5.76). As part of this study, we developed the first synthetic strategy for the synthesis of a 4-fluoro-1,3-thiazole to be reported outside the patent literature. In a final study, starting from 2,5-dibromo-1,3-thiazole (3.3), we also generated a 5-carboxy-1,3-thiazole-based liquid crystal (compound 6.8) which is a structural isomer of the 2- and 5-alkoxy-1,3-thiazole-based liquid crystals described above, in which the positions of the phenyl and 1,3-thiazole rings are transposed. In addition to reporting phase transition temperatures for all synthesized mesogens, we also present the results of several electro-optical studies for the 2-alkoxy-, 5-alkoxy-, and 5-alkoxy-4-fluoro-1,3-thiazole-based liquid crystals (compounds 4.12, 2.12, and 5.76, respectively), all of which were found to be free of chevron defects.

Indexing (document details)
Advisor: Sampson, Paul, Seed, Alexander
Commitee: Basu, Soumitra, Bos, Philip, Ellman, Brett, Twieg, Robert
School: Kent State University
Department: Chemistry
School Location: United States -- Ohio
Source: DAI-B 78/11(E), Dissertation Abstracts International
Subjects: Organic chemistry
Keywords: 3-thiazole, 4-fluoro-1, Alkoxy-1, Carboxy-1, Dibromo-1, Synthetic organic chemistry
Publication Number: 10631080
ISBN: 978-0-355-01379-5
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