Synthesis and study the liquid crystalline properties of compounds containing benzoxazole core and terminal vinyl group

ABSTRACT

Terminal vinyl-based benzoxazole liquid crystalline compounds, 2-(3-fluoro-4ʹ-alkoxy-1,1ʹ-biphenyl −4-yl)-5-(2-propenyloxymethyl)-benzoxazole (nPPF(2)BP), were synthesised and their structures were confirmed by infrared (IR) spectra, proton nuclear magnetic resonance (¹H-NMR) spectra, gas chromatography with electron impact-mass spectrometry (GC/EI-MS), matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry and elemental analysis (EA). The compounds show enantiotropic smectic/nematic phases with mesophase ranges are 71–97 °C and 87–136°C on heating and cooling processes for nPPF(2)BP, respectively. They give low melting points due to lateral fluoro substituent and flexible terminal 2-propenyloxymethyl chain. It is found that the compounds nPPF(2)BP with shorter alkoxy chain (n = 3, 4) exhibit a wide range of nematic mesophase, which is ascribed to enhanced π–π interaction caused by terminal vinyl moiety, whereas further elongation of the terminal alkoxy chain results in supressing nematic phase and increasing smectic mesophase. Compared with methyl terminated analogues, 2-propenyloxymethyl terminated compounds nPPF(2)BP display much lower melting points and wider or comparable mesophase range both in heating and cooling.

GRAPHICAL ABSTRACT

KEYWORDS:

• Benzoxazole-based compounds
• enantiotropic smectic/nematic phases
• lateral fluoro substituent
• terminal vinyl group

Acknowledgments

The authors thanks for the financial support by National Science Foundation Committee of China (51773112, 21673134), Program for Science & Technology Innovation Team of Shaanxi Province (2018TD-030), Ministry of Education Joint Fund (6141A02022219) and the Fundamental Research Funds for the Central Universities (GK201801001, GK201703030).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Fundamental Research Funds for the Central Universities [GK201801001, GK201703030];Ministry of Education Joint Fund [6141A02022219];National Science Foundation Committee of China [51773112, 21673134];Program for Science & Technology Innovation Team of Shaanxi Province [2018TD-030];