Synthesis and mesomorphic properties of banana-shaped compounds derived from 2,7-dihydroxynaphthalene
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Thirty eight compounds composed of achiral banana-shaped molecules belonging to three new homologous series have been synthesized and their mesomorphic properties investigated. The mesophases have been characterized using a combination of polarized light microscopy, differential scanning calorimetry, miscibility methods and X-ray diffraction measurements. All the compounds reported exhibit mesomorphic properties. Most of the homologues in the three series show B1 and B2 phases and the transition temperatures of these are lower in the fluoro substituted compounds. Some of the lower homologues of the fluoro substituted derivatives also show the nematic phase.Keywords:
Miscibility
Homologous series
Polarized light microscopy
Abstract The phase transition temperatures of the liquid crystal 4‐[4‐n‐hexyloxybenzylideneamino]‐azobenzene have been investigated by the thermal microscopy and the Differential Scanning Calorimetric (DSC) studies. These studies confirm that this mesogen exhibits nematic, smectic A and smectic B phases. The transition enthalpies, transition entropies and also the textures exhibited by the different phases are presented.
Azobenzene
Mesogen
Polarized light microscopy
Transition temperature
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We have designed novel liquid crystal oligomers in which three mesogenic units are connected via 3,5‐dihydroxybenzoic acid. 4‐Cyanobiphenyl‐4′‐yl 3,5‐bis{6‐[4‐(5‐octylpyrimidin‐2‐yl)phenyloxy]hexyloxy}benzoate and 4‐(5‐octylpyrimidine‐2‐yl)phenyl 3,5‐bis{6‐[4‐(5‐octylpyrimidine‐2‐yl)phenyloxy]hexyloxy}benzoate have been prepared, and their physical properties investigated by optical microscopy and differential scanning calorimetry. The Y‐shaped liquid crystal oligomers were found to show a direct phase transition from isotropic liquid to anticlinic SmC (SmCanti) phase.
Mesogen
Polarized light microscopy
Crystal (programming language)
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A series of new rod-shaped liquid crystal, 6-methoxy-2-(4-alkyloxybenzylidenamino) benzothiazoles possessingeven numbers of carbon atoms at the alkyloxy chain (C n H 2n+1 O-, n = 10, 12, 14, 16, 18) are prepared and characterized. The phase behaviour of these new compounds was studied by differential scanning calorimetry and polarising optical microscopy. All members exhibited mesophase. Influence of alkyl chain length on the mesomorphic properties was studied. Enantiotropic nematic phase was identified in all the members except for n = 18. Lower member (n = 10) exhibited monotropic (metastable) smectic A phase. The enantiotropic smectic A phase was observed from n -dodecyloxy derivatives onward to the last homologous synthesized.
Homologous series
Metastability
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Synthesis, characterization and phase transition studies in 4-hexyloxy benzylidene 4’-alkoxyanilines
Synthesis and the characterization through polarizing optical microscope (POM) textures in number of 4-hexyloxy benzylidene 4'-alkoxyanilines, 6O.Om with m = 4, 6 to 10 liquid crystalline materials are carried out. Furthermore, the density and thermal expansion coefficient results reveal that the phase transitions present, viz., isotropic–nematic, nematic–SmC and SmC–SmI show first-order nature as expected. The transition temperatures obtained thorough the differential scanning calorimetry is found to be in agreement with the literature data. The first two compounds exhibit only the nematic phase while the next four compounds show enantiotropic SmC phase as per the literature data. The compound with m = 10 exhibits monotropic SmI phase. However, we, the authors, are able to observe this phase in addition to SmC and nematic through POM only as per the literature. The parameters calculated across the phase transitions and in the phases are in agreement with the body of the data available.
Characterization
Polarized light microscopy
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Abstract A homologous series of chiral thiolactate liquid crystals, alkyl 2-[4-(4-decyloxyphenyl)benzoyloxyphenyloxy]thiopropionates, ADBPT-n (n=2–6), was prepared from (R)-2-(4-hydroxyphenoxy)propionic acid. Structural effects on the mesomorphic and physical properties were investigated in terms of variation in the length of alkyl chain attached to the thiolactate group. The mesophases and their corresponding transition temperatures were identified by polarizing optical microscopy and differential scanning calorimetry. Compound ADBPT-4 exhibited SmA* and SmC* phases, whereas other compounds in the series exhibited the SmA* phase along with unidentified SmX1* and SmX2* phases. The maximum P s value measured for ADBPT-4 in the SmC* phase was 17.5 nC cm−2, suggesting the polarization of the material is rather low. The tilt angles were also measured, reaching a maximum of 48 degree.
Homologous series
Polarized light microscopy
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The synthesis and characterization of a new homologous series of compounds, the 2-cyano-1,3-phenylene bis[4-(4-n-alkoxyphenyliminomethyl)benzoates] derived from 2-cyanoresorcinol is reported. All the compounds are enantiotropic mesogens and exhibit the fascinating B7 mesophase. The characterization of the mesophase was performed using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies.
Homologous series
Benzoates
Characterization
Polarized light microscopy
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Abstract The experimental investigation of the induced smectic phase (ISP) phenomenon in the binary system of the homologous series of alkyl cyano phenylcyclohexane (PCH) and 4-n-hexyloxyphenyl 4'-pentyl benzoate ester (5.0.6) is reported. The phase transition temperatures were determined by differential scanning calorimetry and the optical textures were observed through a polarizing microscope in conjunction with a hot-stage. We found that the ISP-effect on equimole mixture of PCH and 5.0.6 increased sharply with the increasing of the length of terminal alkyl chain. By comparing PCH with Cyanobiphenyl (CBP) we also found that the ISP-effect was influenced by molecular framework.
Homologous series
Polarized light microscopy
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Abstract The phase behaviour of blends of poly(ethylene oxide) (PEO) with the liquid crystal p-azoxyanisole (PAA) has been studied by differential scanning calorimetry and optical microscopy. This system exhibits partial miscibility of the components in the molten state (at temperatures above 337 K). The melting temperature and enthalpy of the PAA phase has been found to depend on the blend composition, whereas the melting behaviour of the polymer phase remains quite unaltered. The occurrence of the PAA nematic phase, dispersed within an isotropic liquid phase, has been observed at high concentrations of liquid crystal. The morphology of the blends in the solid state changes largely with the PAA content, depending on the solubility of the components in the liquid phase.
Miscibility
Morphology
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We report the synthesis and properties of a homologous series of asymmetrically substituted 4-(5-(4-benzyloxyphenyl)-1,3,4-oxadiazol-2-yl)phenyl 2-X-4-dodecyloxybenzoates, which have pronounced hockey-stick molecular architectures. The structure was varied through the lateral substitution with various groups, X (H, Me, MeO, Cl, F) in the outer benzene ring. The effect of the lateral group on liquid crystal phase behaviour was investigated by thermal optical microscopy and differential scanning calorimetry. Nematic and dark conclomerate phases were observed with both displaying macroscopically chiral domains.
Homologous series
Polarized light microscopy
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This study describes the novel synthesis of a homologous series of quinoline-containing liquid crystalline 2-(4-alkylphenyl)-6-methoxyquinolines (nPQOMe, n = 4–8) compounds. Preparation of these compounds was completed in the overall two-step reaction and fair to good yields (47–60%) were obtained. Thermotropic behaviors of these liquid crystalline compounds were investigated using differential scanning calorimetry and polarized optical microscopy. Liquid crystals of these 2-(4-alkylphenyl)-6-methoxyquinolines display only nematic phase.
Thermotropic crystal
Homologous series
Polarized light microscopy
Quinoline
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