Mesophase behaviour of 1,2,3-triazole-based nematic liquid crystals influenced by varying alkyl chains and halogen atom substitution

ABSTRACT

To develop novel nematic-phase liquid-crystal (LC) materials with practical potential in optical and photovoltaic devices, the alkyl chain and halogen atom substitution in 1,2,3-triazole-based compounds were varied, and the effects on the mesophase behaviour were investigated. The 4-(4-propylcyclohexyl)phenyl 4-(1-alkyl-5-hydro/halo-1,2,3-triazol-4-yl)benzoate series 1 was successfully synthesised through tandem aerobic oxidative halogenation and click reaction via in situ activation. Except for 5-thiophene-1,2,3-triazole compound 1c-Th displaying no mesomorphism, the other compounds 1 form enantiotropic nematic mesophases, among which compounds 5-hydro-1,2,3-triazole 1c-H (C10) and 1d-H (C12) (long straight chain compounds) form two mesophases (smectic C phase and nematic phase). For 5-halo-1,2,3-triazole compounds 1c-X (× = halide), the mesomorphic temperature range was wider than for the corresponding compound 1c-H because of the effect of the halogen atom substituent on the triazole. Density functional theory (DFT) analysis showed that the structure-property relation for series 1c-X(H) could be defined by using the calculated dihedral angles, dipole moment, polarisability, and molecular electrostatic potential as parameters. Notably, introducing halogen atoms at the 5-position of 1,2,3-triazole can greatly broaden the mesogenic temperature range, ascribed to the weak intermolecular forces and large dipole moment in this class of compounds.

GRAPHICAL ABSTRACT

KEYWORDS:

• Nematic phase
• click chemistry
• halogen atom substitution effect
• triazoles
• DFT calculations

Acknowledgements

The support of this research by the National Natural Science Foundation of China (Fund numbers 21772135, 51773140 and 51973143) is gratefully acknowledged. We would like to thank Editage (www.editage.cn) for English language editing.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [21772135,51773140,51973143]