Browsing by Author "Win, Yip-Foo"

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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.
Mesogenic Schiff base esters with benzothiazole core: synthesis and phase transition studies
(2010)
Ha, Sie-Tiong
;
Koh, Teck-Ming
;
Yeap, Guan-Yeow
;
Lin, Hong-Cheu
;
Lee, Siew-Ling
A series of new rod-shaped mesomorphic compounds, 6-ethoxy-2(4-alkanoyloxybenzylidenamino)benzothiazoles, consisting of a 2,6-disubstituted benzothiazole core and a Schiff base central linkage, were synthesized and their structures were ascertained via elemental analysis and spectroscopic techniques. Their mesomorphic properties were studied using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD) analysis. All compounds showed enantiotropic mesomorphism. Whilst the lower members of the series, hexanoyloxy and octanoyloxy derivatives exhibited nematic phase, the higher members (decanoyloxy, dodecanoyloxy, tetradecanoyloxy, hexadecanoyloxy and octadecanoyloxy derivatives) exhibited nematic and smectic C phases.
Synthesis and mesomorphic behaviours of a homologous series of 2-(4-alkyloxybenzylidenamino)benzothiazoles
(2014-11-02)
Foo, Kok-Leei
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Ha, Sie-Tiong
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Win, Yip-Foo
;
Yeap, Guan-Yeow
;
Lin, Hong-Cheu
The synthesis and characterisation of a series of new rod-shaped liquid crystal (LC), 2-(4-alkyloxybenzylidenamino)benzothiazoles possessing even number of carbon atoms at the alkyloxy chain (CnH2n + 1O-, n=2, 4, 6, 8, 10, 12, 14, 16, 18) are reported. The molecular structures of title compounds were elucidated using FTIR and nuclear magnetic resonance spectroscopic techniques. The phase behaviour of these new compounds was characterised and studied by differential scanning calorimetry and polarising optical microscopy. Lower members (n=2, 4 and 6) did not exhibit mesophase. Octyloxy derivative was monotropic LC. Enantiotropic smectic A phase was observed from n-decyloxy derivatives onward to the last homologous synthesised.
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.
Synthesis and Mesomorphic Properties of 6-Methoxy- and 6-Ethoxy-2-(2-Hydroxy-4-Alkanoyloxybenzylidenamino)Benzothiazoles
(2010)
Ha, Sie-Tiong
;
Koh, Teck-Ming
;
Yeap, Guan-Yeow
;
Lin, Hong-Cheu
;
Lee, Siew-Ling
Two new series of Schiff base thermotropic liquid crystals, 6-methoxy-2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles and 6-ethoxy-2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles, comprising different terminal groups, a methoxyl and ethoxyl group, respectively, were synthesized. Structural elucidation was carried out using elemental analysis and spectroscopic techniques such as Fourier transform infrared (FTIR), 1H and 13C nuclear magnetic resources (NMR), and mass spectrometry. The mesomorphic properties and thermal stabilities of the title compounds were studied by using differential scanning calorimetry, optical polarizing microscopy, and thermogravimetric analysis. No liquid-crystal phases were observed for the short-chain members (n=2 and 3) in both series, and the remaining members all exhibited nematic phase with Schlieren or marble-like textures. Effects of the lateral hydroxyl group, terminal group, and the length of the terminal alkanoyloxy chain on the mesomorphic properties are discussed. Structure-property relationships were established upon comparison with other structurally related compounds.
Synthesis and phase transition behaviours of laterally substituted liquid crystals containing methylhydroquinone: emerging of smectic C phase for higher homologues
(2017-01-01)
Seou, Chi-Kien
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Ha, Sie-Tiong
;
Lee, Siew-Ling
;
Yeap, Guan-Yeow
;
Lin, Chien-Min
A series of laterally substituted low-molar-mass liquid crystals with molecular geometry were constructed with three phenyl rings bridged through ester central groups as the rigid core and a lateral methyl group as the flexible part of a molecule, with a view to understanding and establishing the effect of molecular structure on liquid crystal behaviour. Low-molar-mass mesogens known as 1,4-bis[(4-n-alkyloxybenzoyl)oxy]toluene with different number of carbon (n) at the alkyl chain have been prepared. Their molecular structures were proposed via physical measurements and spectroscopic techniques. Mesomorphic properties were studied by using differential scanning calorimetry, optical polarizing microscopy and powder X-ray diffraction techniques. The results showed that the melting points as well as the clearing temperatures decreased upon lengthening of the terminal alkyloxy chain lengths. Members with the shorter chain (n = 2-10) exhibited nematic phase. As for higher homologues, members with n = 12, 14, 16 and 18 showed polymorphism, whereby these compounds displayed both smectic and nematic properties.