Synthesis and properties of benzoxazole-based liquid crystals containing ethynyl group

ABSTRACT

Series of heterocyclic compounds containing ethynyl group, 2-[4-[2-[4-(alkoxy)phenyl]ethynyl]phenyl] -benzoxazole derivatives (nPEPBx), are prepared and investigated. They display enantiotropic nematic and smectic mesophases with large mesophase ranges of 30–133°C (heating) and 31–141°C (cooling). Compared with reference analogues without ethynyl group, the compounds nPEPBx roughly give lower melting points and much higher nematic mesophase stability because of the introduction of triple carbon-carbon bond. Meanwhile, they show much higher birefringence (Δn, 0.50–0.65 and 0.55–0.68 for experimental and calculated values with density functional theory (DFT), respectively) than common tolane-based liquid crystals, which indicates that the introduction of benzoxazole unit is an effective method to enhance Δn values of the rod-like molecule. It is concluded that nPEPBx has a potential application in liquid crystal mixture as a dopant to enhance the performance of the host mixture.

GRAPHICAL ABSTRACT

KEYWORDS:

• Benzoxazole-based compounds
• ethynyl group
• birefringence
• density functional theory
• liquid crystals

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

The authors thank for the financial support by National Science Foundation Committee of China [51773112, 51873100, 21673134]; Program for Science & Technology Innovation Team of Shaanxi Province [2018TD-030] and the Fundamental Research Funds for the Central Universities [GK201801001, GK201703030].