Synthesis, characterisation and mesomorphic behaviours of non-symmetrically substituted 1,2,4- and 1,3,4-oxadiazole derivatives

ABSTRACT

Two series of non-symmetrically substituted bent-core mesogens derived from the central 3,5 and 2,5 cores of the 1,2,4- and 1,3,4-oxadiazole derivatives, respectively, containing ether and ester linkage have been synthesised by several straightforward synthetic procedures, and their mesomorphic behaviour was studied by optical polarising microscopy (OPM) and differential scanning calorimetry (DSC). The last five homologues of the 1,2,4-oxadiazole series exhibit a monotropic nematic phase on cooling, while the 1,3,4-oxadiazole derivatives do not show any liquid crystalline properties but rather a crystal to isotropic transition is observed by OPM. We show that the bent angles of the 1,2,4- and 1,3,4-oxadiazole rings are crucial in observing the liquid crystal (LC) phases formed, and also that the length of the alkyl substituent is observed to have a significant effect on the nature of the LC phases.

Graphical Abstract

KEYWORDS:

• 1,3,4-oxadiazole
• 1,2,4-oxadiazole
• liquid crystals
• mesomorphic

Acknowledgements

We thank Mr Mohanad H. Masad (Al al-Bayt University, Jordan) for help with the elemental analysis and the ¹H-NMR spectra, and Dr Dhafir Al-Heetimi (Baghdad University) for carrying out the DSC thermographs. Also, many thanks go to the staff of the chemistry department at Al-Mustansiriyah University for supplying us with chemicals. The authors thank the Arab Science Technology Foundation (ASTF) for supplying the OPM with a hot-stage.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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