Synthesis and characterization of new mesogenic esters derived from 1,2,4-oxadiazole and study the effect of alkoxy chain length in their liquid crystalline properties

ABSTRACT

In this study, a new series of non-symmetrically 3,5-disubstituted of 1,2,4-oxadiazole derivatives, 4-[5-(4-methylphenyl)-1,2,4-oxadiazol-3-yl]-phenyl-4-alkoxybenzoate (G₁–G₁₁), which containing ether and ester linkages in the same molecule, is synthesized using different synthetic procedures and their structures are confirmed by several spectroscopic techniques (FT-IR and ¹H nuclear magnetic resonance). The mesomorphic properties of these compounds are studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM); all these derivatives exhibited as mesogens and displayed an enantiotropic liquid crystal with nematic texture, the nematogenic phase of these materials was appeared in wide temperature ranges on heating and cooling cycles that were observed by POM and DSC. The influence of 1,2,4-oxadiazole ring and the elongation of alkyl chain in the mesomorphic properties of this series were investigated. The mesogenic behaviour of this series was compared with the compounds possessing a somewhat similar structure.

Graphical Abstract

KEYWORDS:

• 1,2,4-Oxadiazole
• mesomorphic
• liquid crystalline
• ester mesogens

Acknowledgements

The authors thank Chemistry Department at Al-Mustansiriyah University to provide them with all the necessary requirements for the completion of this study by providing materials and some analysis available within the department. We also thank Dr. Dhafir Al-Heetimi at University of Baghdad and Dr. Mohanad H. Masad at Al al-Bayt University in Jordan for helping us in ¹H NMR and DSC analyses, respectively. Likewise, an abundance of thanks and regard to ASTF (Arab Science and Technology Foundation) for supplying our department with optical polarizing microscopy equipped with hot stage.

Disclosure statement

No potential conflict of interest was reported by the authors.