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ABSTRACT
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 (CH3O, CH3, 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 (ΔαM). 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.
Graphical Abstract
Acknowledgments
The authors gratefully acknowledge the cooperation and help of Magdi M. Naoum, Prof. of Physical Chemistry, Department of Chemistry, Cairo University for his helping in the discussion.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Correction Statement
This article has been corrected with minor changes. These changes do not impact the academic content of the article.