Alkanoyloxy Chain Research Articles

SYNTHESIS AND MESOGENIC PROPERTIES OF NEW AROMATIC SCHIFF BASE’S ESTERS

A homologous series of new Schiff base’s esters, 4-bromobenzylidene-4’-alkanoyloxyanilines were syn-thesized. The structure of the synthesized compounds was elucidated using IR and NMR spectroscopic techniques along with mass spectrometric method. Nine homologous members were prepared whereby the length of alkanoyloxy chain, Cn-1H2n-1COO is varied from n = 2, 4, 6, 8, 10, 12, 14, 16 and 18. Their thermotropic properties were analyzed using differential scanning calorimetry and polarized optical mi-croscopy techniques. Whilst short chain members (number of carbons, n = 2, 4) are non-mesogens, member with n = 6 exhibited monotropic smectic A (SmA) phase. As the n increased to 8, this com-pound becomes the only member that exhibited SmA and SmB as enantiotropic phase. Varying from n = 10 to n = 16, these members displayed enantiotropic SmA and monotropic SmB phases. Longest chain member, n-octadecanoyloxy derivatives exhibited only single mesophase (monotropic SmA). The ester linkage and polar terminal (bromo) group in the present series are essential for the smectic polymorphism in Schiff bases

Effect of terminal chain length on mesomorphic behavior and selective reflection of blue phase liquid crystals

ABSTRACT A series of new chiral liquid crystal compounds named Mt4BOPnAB containing (-)-menthyl group has been prepared and characterised by FT-IR and 1H NMR spectra. The series contains nine membersthat vary in the terminal length of the alkanoyloxy chain (C n − 1H2n − 1COO-, where n = 2, 4, 6, 8, 10, 12, 14, 16, 18). The thermal properties and optical properties were investigated by differential scanning calorimetry (DSC), polarising optical microscopy (POM), X-ray diffraction (XRD) and ultraviolet/visible sepctroscopy (UV/Vis). High chiral menthyl group in Mt4BOPnAB molecules triggers the formation of a cubic structure of a blue phase (BPI/II). Increasing the length of the terminal alkanoyloxy group leads to the reduction in T c , narrowing the N* phase, and contributing to the development of the Sc* phase. In addition, only CLCs with short terminal chains (n ≤ 8) show selective reflection of visible light and themochromic behaviors.

New Homologues Series of Heterocyclic Schiff Base Ester: Synthesis and Characterization

A homologous series of liquid crystal bearing with heterocyclic thiophene Schiff base ester with alkanoyloxy chain (CH3(CH2)nCOO–, where n=4, 6, 8, 10, 12, 14, 16) was successfully synthesized through the modification of some reported methods. The structural information of these compounds was isolated and characterized through some spectroscopic techniques, such as FTIR, 1H, and 13C NMR and elemental analysis. Textural observation was carried out using a polarizing optical microscope (POM) over heating and cooling cycles. It was found that all synthesized compounds (3a–g) exhibited an enantiotropic nematic phase upon the heating and cooling cycle with high thermal stability. Moreover, a characteristic bar transition texture was observed for compounds 3f and 3g which have shown transition of nematic-to-smectic C phase. This has been further confirmed by obtaining relative phase transition temperature using the differential scanning calorimetry (DSC).

Mesomorphic Properties and X-Ray Diffraction Studies of 4-Alkanoyloxybenzylidene-4'-fluoroaniline

A new homologous series of Schiff base esters comprising a terminal fluoro substituent was studied. Molecular polarizability is enhanced by the presence of fluoro substituent, subsequently, affecting intermolecular interactions and resulting in smectic molecular arrangement. All members can be differed from the number of carbons at the alkanoyloxy chain (Cn-1H2n-1COO-, n = 10, 12, 14, 16, 18). The structure of the title compound was confirmed by spectroscopic (IR and NMR) techniques along with mass spectrometric analysis. Their mesomorphic properties were studied by using differential scanning calorimetry and optical polarizing microscopy techniques. Early members (n = 10, 12 and 14) exhibited monotropic smectic A phase while the longer chain members (n = 16 and 18) are non mesogenic compounds. X-ray diffraction analysis was used and confirmed monolayer of smectic A phase in n-dodecanoyloxy derivative.

Mesomorphic behaviour of new azomethine liquid crystals having terminal bromo substituent

Abstract A homologous series of azomethine esters, 4-n-alkanoyloxybenzylidene-4′-bromoanilines possessing even number of carbon atoms at the terminal alkanoyloxy chain (Cn−1H2n−1COO–, n = 8, 10, 12, 14, 16, 18) was synthesized and characterized. Whilst n-octanoyloxy to n-dodecanoyloxy derivatives exhibited enantiotropic smectic A and smectic B phases, n-tetradecanoyloxy to n-octadecanoyloxy derivatives possessed enantiotropic smectic A and monotropic smectic B properties. n-Decanoyloxy derivatives demonstrated the optimum exhibition for both smectic A and smectic B phases. It was found that the length of terminal alkanoyloxy chain has an influence on mesomorphic properties.

Heterocyclic benzoxazole-based liquid crystals: Synthesis and mesomorphic properties

Abstract New Schiff base liquid crystals containing benzoxazole core and alkanoyloxy chain at the end group of the molecules (C n −1 H 2 n −1 COO–, n = 14, 16, 18) was synthesized. The present compounds are enantiotropic smectic A liquid crystals. It was also found that the end groups of the molecules and polar chloro substituent at the benzoxazole fragment had effect on the mesomorphic properties.

Mesomorphic behavior of new azomethine liquid crystals having terminal iodo group

A series of azomethine esters, 3-hydroxy-4-{[(4-iodophenyl)imino]methyl}phenyl alkanoates possessing even number of carbon atoms at the terminal alkanoyloxy chain (Cn-1H2n-1COO-, n = 4,6,8,10,12,14) was synthesized. n-Butanoyloxy was found non-mesogenic, whilst n-hexanoyloxy to n-tetradecanoyloxy exhibited enantiotropic smectic A phase with fan-shaped texture. It was found that the length of terminal alkanoyloxy chain influenced the mesomorphic properties.

Synthesis and Mesomorphic Properties of 6-Methoxy- and 6-Ethoxy-2-(2-Hydroxy-4-Alkanoyloxybenzylidenamino)Benzothiazoles

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 of new schiff base ester liquid crystals with a benzothiazole core

A series of new calamitic liquid crystals, 6-methoxy-2-(4-alkanoyloxybenzylidenamino)benzothiazoles, comprising a benzothiazole core, terminal methoxy group and a Schiff base linkage were synthesised and characterised. This series comprises 12 members wherein members differ by the length of the alkanoyloxy chain (C n-1H2n-1COO-, where n = 2–8, 10, 12, 14, 16, 18). Their mesomorphic properties were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. The short chain derivatives (n = 2 and 3) were non-mesogenic compounds, while an enantiotropic nematic phase was present throughout the remaining members of the series. The smectic C phase emerged from the decanoyloxy derivative onwards.

New Schiff Bases with Pyridine Core: Spectral, Thermal and Optical Characterizations

Problem statement: Numerous studies have been conducted on the Schiff base's alkyl and alkyloxy possessing aromatic core. However, the thermo tropic properties of Schiff base's ester (or alkanoyloxy) with pyridine core was rare studied. Approach: To study spectral, thermal and optical behaviors of Schiff base ester possessing heterocyclic (pyridine) terminal core. A series of 4-[(pyridin-3-ylmethylene) amino] phenylalkanoates were prepared and all the members are differed by the length of alkanoyloxy chain, Cn-1H2n-1COO, where n = 12, 14, 16 and 18. The thermal and optical characteristics were studied using differential scanning calorimetry and polarizing optical microscopy. Results: DSC studies showed that all of the title compounds exhibited direct isotropization and recrystallization during heating and cooling cycles, respectively. Under polarizing optical microscope, crystal phase texture was observed to change to dark region isotropic without displaying any liquid crystal phase. Conclusion: The presence of terminal pyridine core suppressed the formation of mesosphere in the compounds studied.

New Mesogenic Schiff Base Esters with Polar Chloro Substituent: Synthesis, Thermotropic Properties and X-Ray Diffraction Studies

Problem statement: Many studies have been conducted on the Schiff base’s alkyl and alkyloxy possessing terminal halogen substituent. However, the thermotropic properties of Schiff base’s ester (or alkanoyloxy) with chloro terminal group remained unstudied. Approach: Synthesis a series of new Schiff base ester possessing polar chloro group and investigate its mesomorphic properties. The title compounds were prepared via condensation and esterification reactions. The molecular structures were confirmed using spectroscopic techniques. All the members are differed by the length of alkanoyloxy chain, Cn-1H2n-1COO, where n = 2-8, 10, 12, 14, 16 and 18. The mesomorphic properties were studied using differential scanning calorimetry, polarizing optical microscopy and temperature-dependent X-ray diffractometry. Results: Whilst short members (n = 2-5) were not mesogenic compounds, n-hexanoyloxy and n-heptanoyloxy derivatives exhibited monotropic SmA and SmB phases. Enantiotropic smectogenic A and monotropic smectogenic B were observed in n-octanoyloxy to n-hexadecanoyloxy derivatives. Highest member of the series, n-octadecanoyloxy derivatives exhibited monotropic SmA phase. Conclusion: The ester linkage and polar terminal group in the present series are essential for the formation of liquid crystal phase in Schiff bases.

Mesogenic aromatic esters with sulphur containing alkyl chains

Abstract A new series of aromatic esters, 1 and 2 with a sulphur atom in one of the side chains, is described. They exhibit nematic and/or smectic A/C mesophases as a function of the length of the alkyloxy chain. The presence of sulphur in the 4-position of the alkanoyloxy chain depresses both the clearing and the melting points with respect to the corresponding carbon analogues 3, resulting from the higher conformational mobility of the thiaalkyl chain. In 2, the presence of a methyl group in the 2-position of the alkanoyloxy chain induces a SA phase below room temperature.