# C 3‑Symmetric Photoresponsive Chiral Dopants Based on Tribenzotriquinacene

## TL;DR

This paper introduces new chiral dopants that can change the optical properties of liquid crystals when exposed to light, enabling reconfigurable materials for color displays.

## Contribution

The study introduces C3-symmetric TBTQ-based chiral dopants with high helical twisting power and unusual photoresponsive behavior.

## Key findings

- TBTQ hydrazone dopants show higher helical twisting power (β) than azobenzene dopants.
- The Z isomer of TBTQ hydrazone has unexpectedly higher β values than the E isomer.
- Codoping with hydrazone and azobenzene dopants enables reversible handedness inversion in liquid crystals.

## Abstract

Doping cholesteric liquid crystals (CLCs) with photoresponsive
chiral molecules is an effective strategy for devising responsive
soft materials, as it allows for the phototuning of the noncovalent
interactions in the CLCs, and hence, their helical pitch and optical
properties. Here we describe the use of tribenzotriquinacene-based
(TBTQ) hydrazone and azobenzene chiral dopants in the modulation of
the helical pitch of the LC host, 5CB. The unique C
3-symmetry of the TBTQ scaffold enhances the noncovalent
interactions with the host and thus the chiral information transfer,
resulting in helical twisting power (β) values as high as 147
μm–1. Notably, the TBTQ hydrazone exhibits
an unusual deviation from trends observed so far in previous studies,
resulting in larger β values for the Z isomer
rather than the E one. Moreover, the overall β
values for the hydrazone-based dopants are unexpectedly higher than
those of the azobenzene dopants. These results indicate that the host/guest
interactions are better when the photoswitchable chiral dopant is
more rigid, as is the case with the H-bonded Z state
of the hydrazone. The large β values and excellent miscibility
of the hydrazone-based dopants in 5CB allowed us to design films that
reflect visible structural color. The properties of the azobenzene-based
dopants precluded their use in such applications. By codoping 5CB
with hydrazone and azobenzene derivatives of opposite chirality, we
demonstrated reversible handedness inversion upon photoswitching,
providing a versatile soft material platform for reconfigurable photonic
materials and colorimetric display technologies.