Cyanobiphenyl- and Cyanoterphenyl-Based Liquid Crystal Dimers (CB<i>n</i>CT): The Enantiotropic Twist-Bend Nematic Phase

Cyanobiphenyl- and Cyanoterphenyl-Based Liquid Crystal Dimers (CB<i>n</i>CT): The Enantiotropic Twist-Bend Nematic Phase

We report the first homologous series of methylene-linked cyanobiphenyl- and cyanoterphenyl-based liquid crystal (LC) dimers (CB<i>n</i>CT). To induce the heliconical twist-bend nematic (N<sub>TB</sub>) phase through bent molecular shapes, the CB<i>n</i>CT homolog...

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Bibliographic Details
Main Authors: Yamato Shimoura, Yuki Arakawa
Format: Article
Language:English
Published: MDPI AG 2025-01-01
Series:Crystals
Subjects:
liquid crystal dimer
twist-bend nematic phase
cyanoterphenyl
cyanobiphenyl
birefringence
Online Access:https://www.mdpi.com/2073-4352/15/2/120
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Summary:We report the first homologous series of methylene-linked cyanobiphenyl- and cyanoterphenyl-based liquid crystal (LC) dimers (CB<i>n</i>CT). To induce the heliconical twist-bend nematic (N<sub>TB</sub>) phase through bent molecular shapes, the CB<i>n</i>CT homologs have an odd-numbered flexible alkylene spacer (<i>n</i>) ranging from 1 to 17. Polarized optical microscopy and differential scanning calorimetry are used to identify phases and analyze the phase-transition behavior. Except for <i>n</i> = 1, all the CB<i>n</i>CT homologs exhibit the conventional nematic (N) and N<sub>TB</sub> phases. The CB<i>n</i>CT dimers with <i>n</i> = 3 and 5 show a monotropic N<sub>TB</sub> phase, while those with <i>n</i> = 7, 9, 11, 13, 15, and 17 demonstrate an enantiotropic N<sub>TB</sub> phase below the conventional N phase temperature. The N<sub>TB</sub> phases of the CB<i>n</i>CT dimers (<i>n</i> = 7, 9, and 11) remain stable down to room temperature and vitrify without crystallization. Compared with cyanobiphenyl-based LC dimer homologs (CB<i>n</i>CB), the CB<i>n</i>CT dimers show significantly broader N and N<sub>TB</sub> phase temperature ranges with higher isotropic and N<sub>TB</sub>–N phase-transition temperatures. The N<sub>TB</sub> phase temperature ranges of CB<i>n</i>CT (<i>n</i> = 7, 9, 11, and 13) are over 100 °C. Additionally, more CB<i>n</i>CT homologs exhibit the enantiotropic N<sub>TB</sub> phase than the CB<i>n</i>CB ones. These enhancements result from increased π-conjugation and asymmetric molecular structures. Furthermore, CB9CT exhibits higher birefringence than CB9CB owing to its longer π-conjugated terphenyl moiety.
ISSN:2073-4352

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