Teck-Ming Koh

Heterocyclic benzothiazole-based liquid crystals: synthesis and mesomorphic properties

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's base ether with dimethylamino end group

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 molecules 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

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 of New Schiff Base: 4-[(Pyridin-3-ylmethylene)- amino]phenyldodecanoate

A new Schiff base 4-[(pyridin-3-ylmethylene)amino]phenyldodecanoate was synthesized via Steglich esterification. IR, 1H NMR, 13C NMR and MS spectroscopic data are presented.

Phase transition behaviours of calamitic liquid crystals comprising phenylbenzothiazole core

A series of new calamitic liquid crystals 2-[4-(4-alkyloxybenzoyloxy)-phenyl]benzothiazoles comprising a benzothiazole core, terminal alkyl chain and an ester linkage were synthesised and characterised. This series consists of 13 members, wherein the members differ by the length of alkyloxy chain (C n H2n+1O−, where n = 2–10, 12, 14, 16, 18). Their mesomorphic properties were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. Enantiotropic nematic phase was present throughout the series, i.e. from the lowest member (n = 2) until the highest member (n = 18) of the series. The smectic A phase emerged from the nonyloxy derivative onwards.

Synthesis of a New Liquid Crystal, 3-Hydroxy-4-{[(6-methoxy-1,3-benzothiazol-2-yl)imino]methyl}phenyl Palmitate

A new Schiff base ester comprising of heterocyclic moiety, 3-hydroxy-4-{[(6-methoxy-1,3-benzothiazol-2-yl)imino]methyl}phenyl palmitate was synthesized and its IR, 1H NMR, 13C NMR, elemental analysis and MS spectroscopic data are presented.

Synthesis of a New Heterocycle with Liquid Crystal Properties: 2-(3-Methoxy-4-hexadecanoyloxyphenyl)benzothiazole

A new heterocycle 2-(3-methoxy-4-hexadecanoyloxyphenyl)benzothiazole was synthesized and its IR, 1H NMR, 13C NMR and MS spectroscopic data are presented.

Synthesis of New Schiff Base Ether: p-n-(Dimethylamino)-benzylidene-p-dodecyloxyaniline

A new Schiff base ether, p-n-(dimethylamino)benzylidene-p-dodecyloxyaniline, was synthesized and its IR, 1H NMR, 13C NMR and MS spectroscopic data are reported.

Synthesis of 4-[(4-dimethylaminobenzylidene)amino]phenyl tetradecanoate

A new Schiff base ester, 4-[(4-dimethylaminobenzylidene)amino]phenyl tetradecanoate, was synthesized and its IR, 1H NMR, 13C NMR and MS spectroscopic data are reported.

Synthesis of 2-(4-Propyloxyphenyl)benzothiazole

A new 2-(4-propyloxyphenyl)benzothiazole was synthesized and its IR, 1H and 13C NMR and MS spectroscopic data are presented.