The effect of intermolecular actions on the nematic phase range of tolane-liquid crystals

ABSTRACT

An approach to understand the effect of intermolecular actions on the nematic stability, a series of tolane compounds nH containing intermolecular π–π stacking, dipole–dipole and hydrogen bond interactions, are developed and investigated. Their mesophase behaviour were measured by differential scanning calorimetry (DSC) and polarising optical microscopy (POM), the results show that carboxylic acids nH exhibit high melting points and narrow nematic phase intervals, which are attributed to the too strong intermolecular actions. By disrupting the intermolecular hydrogen bond, their corresponding methyl esters nC have been designed and synthesised. It is interesting to note that these compounds exhibit broad nematic mesophase intervals and low melting points. The above results demonstrate that the interruption of intermolecular actions is an effective way to improve the nematic stability. In addition, the effects of the terminal alkyl chains and the terminal polar groups on the nematic stability were also discussed. Finally, DFT calculations of molecular conformation and dipole moment were conducted to better understanding of the molecular structure–mesomorphic property relationship.

GRAPHICAL ABSTRACT

KEYWORDS:

• Tolane liquid crystals
• nematic mesophase
• hydrogen bond interaction
• DFT calculations

Acknowledgement

We are grateful to Professor Wenliang Wang at Shaanxi Normal University for theoretical calculations.

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]Joint Fund of Ministry of Education[6141A02022219], National Science Foundation Committee of China [21673134, 21543012] and the Fundamental Research Funds for the Central Universities [GK201704008] for financial support of this work.