Non‐symmetrical luminescent 1,2,4‐oxadiazole‐based liquid crystals

Abstract

Thermal and optical behaviours of a series of highly π‐conjugated hockey stick‐shaped non‐symmetrical 1,2,4‐oxadiazoles, with liquid crystalline properties, have been studied. All of them presented liquid crystalline phases, in particular smectic and nematic phases typical of calamitic compounds. Although these substances are thermally less stable than their 1,3,4‐oxadiazole isomers, they showed better liquid crystalline behaviour with lower melting points. UV–visible spectra of compounds 1a–1f in solution displayed similar absorption patterns with maxima around 320 and 350 nm (ε ∼ 2.0–6.0×10⁴ L mol⁻¹ cm⁻¹). All compounds exhibited strong blue fluorescence ( = 405–468 nm) with large Stokes shift (79–117 nm). The quantum yields (Φ_F) are 42–65%, except for compounds 1c and 1f where the yields are 2 and 14%, respectively. These compounds also exhibited blue emission in the solid phase ( = 408–492 nm).

Keywords:

• 1,2,4‐oxadiazoles
• fluorescent LCs
• highly π‐conjugated molecules

Acknowledgments

The authors thank Mrs. Marly da Silveira Soldi (DSC measurements), Prof. Edson Minatti and Haidi Fiedler for free access to photophysical instruments. This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq – Brazil) and Merck (Germany).