Non-symmetrically (1,2,4- and 1,3,4-)oxadiazole homologous: synthesis, characterisation and study the effect of different substituents on their mesophase behaviours

ABSTRACT

We have previously demonstrated that the type of oxadiazole isomers is relatively affected on showing the liquid crystalline properties of the compounds that have the same chemical compositions. In this paper, we presented the synthesis and mesomorphic behaviour of related compounds that possess ester linkage with different substituted groups on para of the phenyl to six derivatives containing 1,3,4-oxadiazole and like another six containing 1,2,4-oxadiazole rings. The formation of these compounds was evidenced by FTIR, ¹H NMR, ¹³C NMR, elemental analysis and mass techniques. Their mesophase behaviours were studied by optical polarised microscopy (OPM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). All of them presented liquid crystalline properties with nematic (N), smectic A (SmA) and smectic C (SmC) phases typically to calamitic compounds. The effect of substituent group nature and the type of oxadiazole isomers on the liquid crystalline properties of these compounds are analysed and discussed.

GRAPHICAL ABSTRACT

KEYWORDS:

• Substituted groups
• 1,3,4-oxadiazole
• 1,2,4-oxadiazole
• liquid crystals
• mesomorphic properties

Acknowledgements

We are very thankful to employees of the Chemistry Department in Al-Mustansiriyah University for the cooperation with us in the completion of the requirements of this study. We extend our thanks to Dr Mohanad H. Masad (Al al-Bayt University, Jordan) and Dr Dhafir Al-Heetimi (Baghdad University) for assisting us in completing the ¹H NMR, ¹³C NMR and DSC analyses, respectively. Also many thanks and respect to ASTF (Arab Science and Technology Foundation), in order to equip our department with OPM and hot stage.

Disclosure statement

No potential conflict of interest was reported by the authors.