Browsing by Author "Koh, Teck Ming"

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New mesogenic Schiff base esters comprising benzothiazole moiety: Synthesis and mesomorphic properties
(2009-09-01)
Ha, Sie Tiong
;
Koh, Teck Ming
;
Yeap, Guan Yeow
;
Lin, Hong Cheu
;
Beh, Jun Kit
A homologous series of Schiff base esters, 6-methoxy-2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles, comprising a benzothiazole moiety as the core was synthesized. All the members of this series exhibited an enantiotropic nematic phase. The azomethine linkage along with the lateral hydroxyl and terminal methoxyl groups were found to exert an effect on the mesomorphic properties. (C) 2009 Sie Tiong Ha. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Synthesis and mesomorphic evaluation of new calamitic liquid crystals containing benzothiazole core
(2011-05-01)
Koh, Teck Ming
;
Ha, Sie Tiong
;
Lee, Teck Leong
;
Lee, Siew Ling
;
Yeap, Guan Yeow
The design and synthesis of new calamitic benzothiazole-based liquid crystals, 2[4-(4-alkyloxybenzoyloxy)-phenyl]benzothiazoles are presented. The target compound was characterized using spectroscopic techniques, such as FT-IR, NMR ((1)H and (13)C), microanalysis and EI-MS. The liquid crystalline behaviours of these compounds were thoroughly examined by differential scanning calorimetry and polarizing optical microscope techniques. These materials exhibited enantiotropic nematic phase with high thermal stability (> 168 degrees C). Smectic A phase starts to emerge as monotropic (metastable) phase from C10 member and changes into enantiotropic (stable) phase from C12 and persists up to C16 members. (C) 2010 Sie Tiong Ha. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Synthesis and mesomorphic properties of new Schiff base esters with different alkyl chains
(2009-07-01)
Ha, Sie Tiong
;
Ong, Lay Khoon
;
Ong, Siew Teng
;
Yeap, Guan Yeow
;
Wong, Joanna Pik Wan
A new series of Schiff base esters, 4-(dimethylamino)benzylidene-4'-alkanoyloxyanilines containing even number of carbons at the end group of the molecules (C(n-1)H(2n-1)COO, n = 6, 8, 10, 12, 14, 16, 18) were synthesized. The present compounds were monotropic liquid crystals. It was also found that the end groups of the molecules had effect on the mesomorphic properties. (C) 2009 Sie Tiong Ha. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.