Synthesis, mesomorphic and fluorescent properties of stilbene-containing 1,3,4-oxadiazole compounds

ABSTRACT

A new class of mesogenic 1,3,4-oxadiazole derivatives 2a-2e based on stilbene has been synthesised and characterised by means of nuclear magnetic resonance (NMR), electro spray ionisation-mass spectrometry (ESI-MS) techniques and elemental analyses. The thermal properties were investigated by means of differential scanning calorimetry (DSC), polarising optical microscopy (POM) and thermogravimetric analyses (TGA). All compounds exhibited enantiotropic liquid crystal behaviours with typical calamitic mesophases (Smectic A (SmA), Smectic C (SmC) and Nematic phases) in very wide temperature range with excellent thermal stability. The nature of the mesophase is determined greatly by the polarity of the terminal groups. The electron-withdrawing cyano (for 2a) and fluoro (for 2b) groups tended to form smectic A phase, while the electron-donating methyl (for 2c), methoxy (for 2d) and decyloxy (for 2e) groups facilitated the SmA or SmC and nematic phases. Out of expectation, no banana phases were found in these mesogens. It’s noted that the solutions of all compounds in CH₂Cl₂ individually displayed one absorption band with λ_max values at 340–355 nm, and exhibited an intense emission with λ_max values at 428–486 nm and photoluminescence quantum yields of 0.39–0.55. The relationship between the molecular structures and mesogenic properties is discussed briefly in this work.

GRAPHICAL ABSTRACT

KEYWORDS:

• Heterocyclic liquid crystal
• 1,3,4-oxadiazole
• fluorescence
• synthesis

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

We are grateful for financial support from the National Training Program of Innovation and Entrepreneurship for Undergraduates [No. 202110055073].