Selenium-linked cyanobiphenyl-based liquid crystal dimers: the effects of chalcogen linkage and spacer length on the twist-bend nematic phase

ABSTRACT

We synthesised selenium-linked liquid crystal dimers and examined their phase behaviour to determine the effects of chalcogen linkage and spacer length on the formation of a twist-bend nematic (N_TB) phase. Two new homologous series of nonsymmetric selenoether- and ether- or thioether-linked cyanobiphenyl-based dimers (CBSenOCB and CBSenSCB, respectively) comprising an alkyl spacer chain with a carbon number (n) of 3, 5, 6, 7, 9, and 11 were developed. We also synthesised n = 6 and 11 of previously reported symmetrically selenoether-linked CBSenSeCB homologues. Conventional nematic (N) and N_TB phases were observed for nearly all odd-n CBSenSeCB, CBSenOCB, and CBSenSCB dimers. The phase transition behaviours of the three homologous series were compared with those of the known symmetric ether-linked CBOnOCB, thioether-linked CBSnSCB, and asymmetric thioether- and ether-linked CBSnOCB dimers. Replacing ether with thioether or selenoether resulted in lower LC phase-transition temperatures, particularly for selenoether. Single-crystal structural analyses revealed that CBS3SCB and CBSe3SeCB exhibited folded U-shaped molecular shapes that were bent more than the V-shapes of CBOnOCB (n = 3 and 5) and CBS5SCB. In addition, thioether and selenoether linkages rendered the molecular forms of odd-spacer dimers in the crystals more bent.

GRAPHICAL ABSTRACT

KEYWORDS:

• Twist-bend nematic phase
• cyanobiphenyl dimer
• chalcogen linkage
• selenoether
• thioether
• ether

Acknowledgments

The authors acknowledge funding from the Japan Society for the Promotion of Science (KAKENHI grant number 20K15351) and Toyohashi University of Technology.

Disclosure statement

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

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/02678292.2024.2302981.

Additional information

Funding

This work was supported by the Japan Society for the Promotion of Science (KAKENHI) under [Grant Number 20K15351] and Toyohashi University of Technology.