Preparation and properties of 1-methyl-1H-benzimidazole-based mesogenic compounds incorporating ethynyl moiety

ABSTRACT

Heterocyclic mesogenic compounds are one of the interesting liquid crystals. Here, a series of 1-methyl-1H- benzimidazole-based mesogenic compounds incorporating ethynyl moiety, 2-[4-[2-[4-(alkoxy)phenyl]ethynyl]phenyl]-1-methyl-1H-1,3-benzimidazole derivatives (nPEPMx) with terminal groups of H, CH₃ and NO₂ (coded as nPEPMH, nPEPMM and nPEPMN, respectively), are synthesised and their properties are evaluated. It is noted that the compounds nPEPMx with short alkoxy chain less than 9 carbon atoms display enantiotropic nematic mesophases, whereas corresponding reference compounds without ethynyl moiety have enantiotropic smectic mesophases. The mesophase ranges of compounds nPEPMx 50–70°C and 55–108°C on heating and cooling for nPEPMH, 76–106°C and 98–142°C for nPEPMM, and 78–132°C and 130–166°C for nPEPMN, respectively. Besides, compounds nPEPMx show obviously large birefringence of 0.501–0.641, suggesting a potential application in liquid crystal mixture. The high birefringence may result from its large π-conjugated molecule structure incorporating ethynyl and benzimidazole π-conjugated mesogenic unit.

GRAPHICAL ABSTRACT

KEYWORDS:

• 1-methyl-1H-1; 3-benzimidazole derivatives
• ethynyl moiety
• birefringence
• enantiotropic nematic mesophases
• liquid crystals

Acknowledgments

The authors thank 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).

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, 21673134]; Program for Science & Technology Innovation Team of Shaanxi Province [2018TD-030]; the Fundamental Research Funds for the Central Universities [GK201801001, GK201703030].