# Chirality inversion in cholesteric phases of bent-shaped liquid crystal dimers with chiral dopants

## TL;DR

This paper shows that adding chiral dopants to bent-shaped liquid crystal dimers can cause helical pitch divergence and chirality inversion in cholesteric phases.

## Contribution

The study reveals chirality inversion and helical pitch divergence in cholesteric phases of bent-shaped LC dimers with chiral dopants.

## Key findings

- Chirality inversion was observed in cholesteric phases of bent-shaped LC dimers with chiral dopants at specific concentrations.
- Helical pitch divergence and reforming with opposite chirality occurred near phase transition temperatures.
- The effect was specific to ester-linked dimers and not observed in other types of dimers.

## Abstract

Incorporating molecular chirality into liquid crystals (LCs) yields nanoscale one-handed helical structures. The helical pitch of a cholesteric (Ch) phase (i.e., a chiral nematic phase) is typically slightly temperature-dependent, and the sense of helical rotation (i.e., chirality) rarely inverts. This study reports helical pitch divergence and chirality inversion in the Ch phase of bent-shaped LC dimers added with a chiral dopant (CD). We prepared four chiral LC mixtures containing equal proportions of two ester-linked 4-(trans-4-pentylcyclohexyl)phenyl-based bent-shaped LC dimers with odd-numbered spacers, each doped with 0.25, 0.50, 1.0, or 2.0 wt% of an isosorbide-based CD, ISO-(6OBA)2. All mixtures exhibited enantiotropic chiral twist-bend nematic and Ch phases near room temperature. Polarized optical microscopy revealed that in the Ch phases of the dimer mixtures with 0.25, 0.50, and 1.0 wt% CD, the helix diverged and reformed with opposite chirality just above the phase transition temperature. The high- and low-temperature Ch phases were identified as right- and left-handed, respectively, using circular dichroism spectroscopy and the contact preparation method. The dimer mixture with 2.0 wt% CD exhibited only helix divergence of the right-handed Ch phase. These phenomena were also observed in each nonblended dimer, but not in other bent-shaped cyanobiphenyl-based twist-bend nematogenic dimers with different linkages. Our findings offer new insights into chirality inversion in LCs and have promising potential for temperature-tunable chiral-switching systems based on bent-shaped LC dimers.

We report helical pitch divergence and chirality inversion in cholesteric phases of bent-shaped liquid crystal dimers added with a chiral dopant.