Lay-Khoon Ong

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.

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.

Influence of Linking Group Orientation on Mesomorphism of Two Aromatic Ring Mesogens

A new homologous series of alkyl 4-{[(4-chlorophenyl)imino]methyl}benzoates were prepared, and all the members are differentiate by the alkoxy chain length, , where –7, 9, 11, 13, 15. Their phase transition behaviors and mesophase characteristics were studied by differential scanning calorimetry (DSC) and optical polarizing microscopy techniques. DSC thermograms show direct isotropization and recrystallization during heating and cooling processes, respectively. The crystal phase changed directly to dark area textures (isotropic phase) without displaying any mesophase. The mesomorphic properties of compounds studied are strongly dependent on the orientation of the ester linkage. Reversed ester linkage has caused depression of mesomorphic property in the compounds studied.

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 and phase transitions studies on Schiff base symmetrical dimers: α,ω-Bis(4-pyridine-3- methyleneaminoxy)alkanes

A series of symmetrical dimers bearing heterocyclic ring, α,ω-bis(4-pyridine-3methylideneaminoxy)alkanes, were prepared and all the members are differed by the spacer length, CnH2n, where n = 6, 8, 10 and 12. Their transition temperatures and mesophase characteristics were studied by differential scanning calorimetry and optical polarizing microscopy techniques. DSC thermograms exhibited direct isotropization and recrystallization during heating and cooling cycles, respectively. The crystal phase texture changed to dark region isotropic without displaying any mesophase. The influence of molecular structure on the mesomorphic properties of symmetrical dimers was studied.

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.