Browsing by Author "Ong, Lay-Khoon"

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Heterocyclic benzothiazole-based liquid crystals: synthesis and mesomorphic properties
(2009)
Ha, Sie-Tiong
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Koh, Teck-Ming
;
Lin, Hong-Cheu
;
Yeap, Guan-Yeow
;
Win, Yip-Foo
Two homologous series of 2-(4-alkanoyloxybenzylidenamino)benzothiazoles and 2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles were synthesised and characterised. Their molecular structures differed wherein the latter comprised a lateral hydroxyl group, unlike the former. Spectroscopic techniques such as FT-IR, 1H 13C NMR and mass spectrometry together with elemental analysis were employed to elucidate the molecular structures. The transition temperatures and their mesophases were determined by differential scanning calorimetry, optical polarising microscopy and X-ray diffraction techniques. Members with decanoyloxy till hexadecanoloxy chain in the series without the lateral hydroxyl group each exhibited a smectic A phase, while those in the series with the lateral hydroxyl group were non-mesogenic. The mesomorphic properties of the present series were compared with other structurally related series to establish the chemical structure-mesomorphic properties relationship.
Heterocyclic pyridine-based liquid crystals: synthesis and mesomorphic properties
(2018-01-01)
Ong, Lay-Khoon
;
Ha, Sie-Tiong
;
Yeap, Guan-Yeow
;
Lin, Hong-Cheu
;
材料科學與工程學系
A series of new calamitic liquid crystals, 4-{[(pyridin-4-yl)methylidene]amino}phenyl 4-alkoxybenzoates comprising a heterocyclic (pyridine) and two phenyl rings core system, terminal alkoxy chain, imine and ester linkers were synthesised and characterised. This series consists of nine members wherein the members differ by the length of alkoxy chain (CnH2n+1O-, where n=2, 4, 6, 8, 10, 12, 14, 16, 18). Spectral analysis results were in accordance with the expected structure. Their thermotropic behaviours were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. A single mesophase (nematic) was observed for the first three members of the series (n=2, 4 and 6). As the alkoxy chain increased to n=8 and n=10, the nematic phase appeared together with an additional smectic A (SmA) phase. When moving from n=12 until the highest members (n=18), the nematic phase disappeared and these compounds only exhibited a single mesophase (SmA). [GRAPHICS] .
Mesogenic Schiff base esters with terminal chloro group: Synthesis, thermotropic properties and X-ray diffraction studies
(2010-05-01)
Ha, Sie-Tiong
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Ong, Lay-Khoon
;
Sivasothy, Yasodha
;
Yeap, Guan-Yeow
;
Lin, Hong-Cheu
A new homologous series of Schiff base esters comprising a terminal chloro substituent was studied. The chloro substituent contributes to the molecular polarizability, thus, affecting intermolecular interactions, hence, resulting in smectic polymorphism. The mesomorphic properties were studied using differential scanning calorimetry, polarizing optical microscopy and temperature-dependent X-ray diffractometry. Whilst the n-pentanoyloxy and n-heptanoyloxy derivatives exhibited enantiotropic smectogenic A and B phases, monotropic smectogenic A and B phases were observed in the n-butanoyloxy and n-hexanoyloxy derivatives. Enantiotropic smectogenic A and monotropic smectogenic B phases were observed in the n-octanoyloxy to n-hexadecanoyloxy derivatives. The highest member of this series, the n-octadecanoyloxy derivative, exhibited an enantiotropic smectogen A phase. The homologous members were compared with structurally related series to establish their chemical structure-mesomorphic behavior relationships.
Mesogenic Schiff's base ether with dimethylamino end group
(2009)
Ha, Sie-Tiong
;
Ong, Lay-Khoon
;
Wong, Joanna Pik-Wan
;
Yeap, Guan-Yeow
;
Lin, Hong-Cheu
A series of Schiff base ethers comprising a dimethylamino group at one terminal position and an even number of carbons at the other along the molecular axis was studied. The dimethylamino unit, acting as a charge-transfer donor in the formation of conjugative interactions, contributes to the molecule's polarizability and in turn affecting its intermolecular interactions, leading to the formation of less-ordered mesophase. The mesomorphic properties were studied using polarizing optical microscopy and differential scanning calorimetry. Whilst the n-butyloxy to n-hexadecyloxy derivatives exhibited nematic phase, the n-ethyloxy, n-propyloxy and n-octadecyloxy derivatives were not mesogenic. Their phase transitions during heating and cooling run were presented. The title compounds were compared with other structurally related series to establish their chemical structure-mesomorphic property relationships.
Synthesis and Mesomorphic Properties of 2-(4-Alkyloxyphenyl)benzothiazoles
(2009)
Ha, Sie-Tiong
;
Koh, Teck-Ming
;
Yeap, Guan-Yeow
;
Lin, Hong-Cheu
;
Boey, Peng-Lim
A homologous series of 2-(4-alkyloxyphenyl)benzothiazoles with an even number of carbons in the terminal alkoxyl chain was synthesized and characterized. The structure of the compounds was postulated using elemental analyses, FT-IR, NMR, and mass spectrometry techniques. Their liquid crystalline properties have been investigated by optical polarizing microscopy, DSC, and X-ray diffraction (XRD) techniques. Whilst the n-octyloxy to n-hexadecyloxy derivatives exhibited a monotropic smectic A phase, the n-ethoxy to n-hexyloxy and the n-octadecyloxy derivatives were not mesogenic. The mesomorphic properties of the present series were compared with other structurally related series to establish the chemical structure-mesomorphic properties relationship.