Improved mesomorphic behaviour and large birefringence of fluorinated liquid crystals containing ethynyl and 1-methyl-1H-benzimidazole moieties

ABSTRACT

With altering molecular dipole moments via lateral fluoro atom and π-conjugation through carbon–carbon triple bond, improved mesomorphic behaviour is achieved for new kind of fluorinated mesogenic compounds containing ethynyl and 1-methyl-1H-benzimidazole moieties, namely, 2-[4-[2-[4-(alkoxy) phenyl]ethynyl]-3-fluorophenyl]-1-methyl-1H-benzimidazole derivatives (nPEF(3)PMx). The compounds nPEF(3)PMx mainly display enantiotropic nematic mesophases with mesophase ranges of 27.1–59.1 °C and 62.7–96.7°C on heating and cooling for nPEF(3)PMH, 59.499.1°C and 96.2–144.6°C for nPEF(3)PMM, and 101.6–109.4°C and 104.9–157.2°C for nPEF(3)PMN (n < 8), respectively. Compared with nonfluorinated reference analogues I, nPEF(3)PMx give obviously lower melting points and much wider or comparable nematic mesophase ranges, meanwhile, they show much lower melting points and higher nematic mesophase stability than reference analogues II because of their reduced molecular dipole moments and enhanced π-conjugation. In addition, the compounds nPEF(3)PMx are composed of benzene ring, ethynyl bridge and benzimidazole mesogenic unit, therefore, they have high birefringence of 0.48–0.62 resulted from their large π-conjugated molecule. The result indicates that nPEF(3)PMx has a potential application in liquid crystal mixture.

GRAPHICAL ABSTRACT

KEYWORDS:

• Fluorinated mesogenic compounds
• 1-methyl-1H-benzimidazole
• ethynyl group
• birefringence
• dipole moment
• nematic mesophases

Acknowledgments

The authors thank for the financial support by National Science Foundation Committee of China (51773112, 51873100 and 21673134), Program for Science & Technology Innovation Team of Shaanxi Province (2018TD-030), and the Fundamental Research Funds for the Central Universities (GK201801001, GK201703030 and 2019TS001).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by National Science Foundation Committee of China [51773112, 51873100, and 21673134]; Program for Science & Technology Innovation Team of Shaanxi Province [2018TD-030]; the Fundamental Research Funds for the Central Universities [GK201703030, GK201801001, and 2019TS001].