Synthesis and mesomorphic properties of laterally fluoro azo/ ester based on four ring compounds with a wide range mesophase thermal stability

New series of compounds were prepared by replacing the lateral methyl and bromo substituents in the previously investigated 4-ring compounds by the strong electronegative and smaller size fluorine atom. The two wings of the rode-shaped molecules, one is a compact polar group (CH 3 O, CH 3 , H, and B...

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Bibliographic Details
Published in:Liquid crystals 2022-04, Vol.49 (5), p.666-678
Main Authors: Ahmed, Nagwa H.S., Saad, Gamal R., Fahmi, Abdelgawad A., Abdelfattah, Ahmed M.
Format: Article
Language:English
Subjects:
Anisotropy
Azo/ester/azo four ring
Bromine
Cyclic compounds
Electronegativity
Fluorine
Homology
lateral f
Lateral stability
Mesophase
mesophase behaviour
Phases
polarisability anisotropy
Polarity
Temperature
Thermal stability
Transition temperatures
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Summary:New series of compounds were prepared by replacing the lateral methyl and bromo substituents in the previously investigated 4-ring compounds by the strong electronegative and smaller size fluorine atom. The two wings of the rode-shaped molecules, one is a compact polar group (CH 3 O, CH 3 , H, and Br), while the other is an alkoxy group with varying chain length that varies between 6-16 carbon atoms. Transition temperatures and temperature ranges of the observed phases were determined by DSC and phases identified by PLM. Except for the terminally methoxy-substituted homologues, which were found to be purely nematogenic, homologues of all the remaining derivatives are dimorphic possessing both N and SmA phases with wide temperature range. The fluoro derivatives were compared with the previously investigated lateral Br and methyl analogues in order to evaluate the effect of the polarity and size of the lateral group on their mesomorphic behaviour and polarisability anisotropy (Δα M ). The comparison revealed that the replacement of lateral substituent by the small-sized strong electronegative fluorine atom is accompanied by an enhancement of thermal stability and temperature ranges of the mesophases compared with lateral Br and methyl substituents. The results were discussed in terms of molecular polarisability and steric effect.
ISSN:0267-8292
1366-5855
DOI:10.1080/02678292.2021.2000053