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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

DIBENZO[a,c]PHENAZINE AND 2,3- DIPHENYLQUINOXALINE DISCOGENS WITH PHENANTHROLINE AND CROWN ETHER, AND FLUOROUS POLYCATENAR LIQUID CRYSTALS

Tzeng, Mei-Chun 06 September 2012 (has links)
In this PhD thesis, there are two major motifs: dibenzo[a,c]phenazine- and 2,3-diphenylquinoxaline novel discogens and fluorous polycatenar liquid crystals. The thermo properties of these new compounds were elucidated using optical microscopy, differential scanning calorimetry and powder X-ray diffraction. In the phenanthroline series (Chapter 2), 1,10-phenanthroline core incorporated into dibenzo[a,c]phenazine structure exhibit columnar mesophases with extremely wide width. X-ray diffraction study pinpoints to that half-shaped mesogens with reduced symmetry has preferential intra-molecular parallel conformation in the mesophase. This molecule has gel ability with different solvents. In dimeric crown ether series (Chapter 3A), 2,3-diphenylquinoxaline-based mesogens containing dibenzo-18-crown-6 has hexagonal columnar mesophase with extremely narrow width. Incorporation potassium metal ion into crown moiety dramatically enhanced mesomorphic stability and for metal complexes, as side chain increases, hexagonal mesophases predominate over rectangular mesophases. Furthermore, both in hexagon or rectangle, per columnar slice consist of two molecules. All of prolonged long glassy formation up to one year at room temperature. In monomeric crown ether series (Chapter 3B), metal-free molecules fail to be mesomorphic, but complexation with lithium and sodium metals enhanced thermo stability and rectangular mesophase (C2mm) were found. Also, per columnar slice was comprised of four molecules. Last (Chapter 4), a series of tri- and tetra-catenar mesogens containing various combinations of hydrocarbon and semiperfluorocarbon chains has been prepared to elucidate the fluorophlic-fluorophobic effect on mesomorphism. Tricatenar with one terminal semiperfluoro- and two hydrocarbon chains are aligned into lamellar periodicity driven by the mutual incompatibility of the hydrocarbon and fluorocarbon portions. But unsymmetric tetracatenar mesogens show rectangular mesophase.

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