Preparation and characterisation of laterally monofluorinated mesogenic benzimidazole-based compounds

ABSTRACT

Series of laterally monofluorinated compounds, 2-(4ʹ-alkoxy-3-fluorobiphenyl-4-yl)-1H-benzimidazole derivatives (nPPF(3)Mx) bearing different substituents (H, CH₃, NO₂, coded as nPPF(3)MH, nPPF(3)MM and nPPF(3)MN, respectively) at 5-position, were prepared and their structures were characterised. According to the results from differential scanning calorimetry and polarising optical microscopy, the present compounds nPPF(3)Mx exhibit enantiotropic smectic mesophases, for which the mesophase ranges are 13–67 and 47–111°C on heating and cooling for nPPF(3)MH, 84–112 and 126–154°C for nPPF(3)MM, and 23–102 and 49–117°C for nPPF(3)MN, respectively. Compared to non-fluorinated analogues, monofluorinated nPPF(3)Mx have low melting/clearing points and display enhanced mesophase range both in heating and cooling, which are attributed to the disruption of the side-to-side intermolecular packing caused by the ortho lateral fluoro substituents and the increased dipole–dipole interaction between the polar fluoro-substituted molecules, respectively. It is noted that nPPF(3)MM and nPPF(3)MN show a much wider mesophase range than nPPF(3)MH, which suggest that the substituent at benzimidazole moiety can improve the mesophase stability.

Graphical Abstract

KEYWORDS:

• Laterally monofluorinated compounds
• benzimidazole derivative
• enantiotropic smectic mesophase
• photophysical properties

Acknowledgements

The authors thanks for the financial support by the Key Technologies R&D Program of Shaanxi Province (2014K10-06), National Science Foundation Committee of China (51373092, 21543012), Special Research Fund for the Doctoral Program of Higher Education (20130202120010), Program for Key Science & Technology Innovation Team of Shaanxi Province (2015KCT-13) and the Fundamental Research Funds for the Central Universities (GK201703030, GK201603058, GK201501007, GK201501002).

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

The authors thanks for the financial support by the Key Technologies R&D Program of Shaanxi Province (2014K10-06), National Science Foundation Committee of China (51373092, 21543012), Special Research Fund for the Doctoral Program of Higher Education (20130202120010), Program for Key Science & Technology Innovation Team of Shaanxi Province (2015KCT-13) and the Fundamental Research Funds for the Central Universities (GK201703030, GK201603058, GK201501007, GK201501002).