Synthesis and physical properties of tolane liquid crystals containing 2,3-difluorophenylene and terminated by a tetrahydropyran moiety

ABSTRACT

Four series of tolane liquid crystals containing 2,3-difluorophenylene and terminated by a tetrahydropyran (THP) moiety have been synthesised via multistep reactions based on 4-alkylcyclohexanecarboxylic acids and 4-bromo-2,3-difluorophenol. Their properties were measured by differential scanning calorimetry, polarising optical microscopy, Abbe refractometer and an electrical constants instrument. The results show that the THP-based liquid crystals nT reveal a relatively high value of the birefringence, negative dielectric anisotropy, good solubility and a broad nematic mesophase. The effects of the terminal alkyl chain, the lateral fluoro substituents and the THP terminal group on the mesomorphic and physical properties are discussed. Meanwhile, density functional theory calculations of molecular conformation and polarisability were conducted to correlate the experimental findings.

GRAPHICAL ABSTRACT

KEYWORDS:

• Tolane liquid crystals
• 2-difluorophenylene
• tetrahydropyran
• DFT calculations

Acknowledgements

We are grateful to Professor Wenliang Wang at Shaanxi Normal University for theoretical calculations at Shaanxi Normal University. We also thank Senior Engineer Jian Li at Xi’an Modern Chemistry Research Institute for testing the dielectric anisotropy.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors would like to thank the Defense Industrial Technology Development Program of China [B0520132007, B1120132028]; Shaanxi National Science Foundation [2014JM7270]; Key Technologies R&D Program of Xian [CXY1430(2)]; the Key Technologies R&D Program of Shaanxi Province [2014K10-06]; Program for Changjiang Scholars and Innovative Research Team in University [IRT-14R33] and the Fundamental Research Funds for the Central Universities [GK201504008, GK201501007, GK201501002] for financial support of this work.