Increasing the negative dielectric anisotropy of liquid crystals with polar substituents parallel to their long molecular axis through adding terminal 2,2-difluoroethyl group

ABSTRACT

A series of 2,3-difluorophenylene-based negative liquid crystals which own different terminal groups has been synthesised in high yields through many classical named reactions such as Suzuki coupling and Williamson etherification. Thermal properties of these mesogens were tested by differential scanning calorimetry and the effects of the terminal groups on the melting points of molecules were evaluated. Dielectric anisotropies of the synthesised molecules were then measured and found that relatively long alkyl substituents would decrease the Δε value when compared with the ethyl. For the compound with a polar substitute on the long molecular axis, the introduction of 2,2-difluoroethyl would increase the negative Δε when it was put into the opposite direction of the original polar group, making this strategy a new access for the improvement of negative Δε. DFT calculations were carried out to analyse the orientation of the dipole moment in molecules and found that the introduction of 2,2-difluoroethyl had changed the orientation of the dipole moment into nearly perpendicular to the long molecular axis, which benefited the growth of the negative Δε value, revealing the mechanism of this strategy from the view of molecular level to some extent.

GRAPHICAL ABSTRACT

KEYWORDS:

• Fluorinated liquid crystals
• negative dielectric anisotropy
• 2,3-difluorophenylene
• 2,2-difluoroethyl
• density functional theory calculation

Acknowledgments

Here the authors would like to thank Dr. Qiang Guo at College of Optoelectronic Engineering, Chengdu University of Information Technology for some useful suggestions and kindly help in the DFT calculations.

Disclosure statement

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

Supplementary data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/02678292.2023.2238659.

Additional information

Funding

This work was supported by grants from Key Research and Development Program of Shaanxi [Program No. 2023-YBGY-457].