Synthesis and mesomorphic properties of the nematic mesophase benzoxazole derivatives with big twist angle of difluoro-biphenyl unit

ABSTRACT

Modifying the position and numbers of lateral fluorine substituent is a common method to design and adjust the mesophase of liquid crystal compounds. Here, a series of 2-(2,2ʹ-difluoro-4ʹ-alkoxy-1,1ʹ-biphenyl-4-yl)-5-substituted benzoxazole with both non-polar (H, CH₃) and polar (NO₂) groups (coded as nPF(2)PF(2)Bx) is synthesised and characterised. All of the compounds show a conspicuous inter-ring twist angle of 38° compared with corresponding reference compounds I and II which are calculated by density functional theory method, and it is interesting to note that the final compounds nPF(2)PF(2)Bx show only nematic mesophase during heating or cooling. Meanwhile, the UV-vis absorption bands and photoluminescence emission peaks both display remarkable blue-shifted. The aforementioned results reveal that lateral difluoro substituents play a key role to stable the nematic mesophase by increasing the dihedral angle of biphenyl.

Graphical Abstract

KEYWORDS:

• Lateral difluoro substituent
• benzoxazole derivatives
• enantiotropic mesophase
• liquid crystal properties

Acknowledgments

The authors thanks for the financial support by National Science Foundation Committee of China (51773112, 21673134), Program for Key Science & Technology Innovation Team of Shaanxi Province (2018TD030), Ministry of Education Joint Fund (6141A02022219) and the Fundamental Research Funds for the Central Universities (GK201801001, GK201703030, 2018CBLZ005).

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by National Science Foundation Committee of China [51773112, 21673134]; Program for Key Science & Technology Innovation Team of Shaanxi Province [2018TD030]; Ministry of Education Joint Fund [6141A02022219];  the Fundamental Research Funds for the Central Universities [GK201801001, GK201703030, 2018CBLZ005].