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ABSTRACT
A new series of liquid crystals consisting of biphenyl unit connected to phenyl core system have been successfully prepared wherein various substituents X= OCH3, F, Cl, Br and I were introduced in the para position of the imine fragment while the length of terminal alkoxy chain of seven carbon atoms was intact. The mesomorphic and thermal studies by POM and DSC exhibit dominant enantiotropic nematic (N) phase. A relatively weak magnetism was detected with vibrating sample magnetometer (VSM) for compounds 3F and 3I at room temperature, wherein the magnetic strength of fluoro-substituted compound appeared stronger than the iodo-substituted compound. The connectivity between the substituents X and their kinetic stability associated with the changes in HOMO-LUMO energy gap value (ΔEgap) supports that the terminal substituents X have great influence on the ΔEgap which can be ascribed to the chemical activity of the compounds. Present study shows an increase in the ΔEgap from OCH3 < I < Br < Cl < F, where the largest ΔEgap indicates high molecular kinetic stability and low chemical reactivity because adding electrons to high-lying LUMO is energetically unfavourable, resulting in disruption of the molecular packing and reduction of nematogenic, which were validated by DSC and POM.
GRAPHICAL ABSTRACT
Acknowledgments
The main author (G.-Y. Yeap) would like to thank Ministry of Higher Education Malaysia for Fundamental Research Grant Scheme (FRGS 2020-1) with Project Code: FRGS/1/2020/STG04/USM/01/2. All researchers are also grateful for the research funding under International Collaborative Research by Soka University (Japan).
Disclosure statement
No potential conflict of interest was reported by the author(s).
Supplementary data
Supplemental data for this article can be accessed online at https://doi.org/10.1080/02678292.2023.2294958.