Light-controllable chiral dopant based on azo-fragment: synthesis and characterization

TL;DR

This paper reports the synthesis and characterization of a novel light-controllable chiral dopant with azo and chiral features, demonstrating reversible isomerization and effects on liquid crystal helical structures under UV/VIS light.

Contribution

The study introduces a new azo-based chiral dopant with reversible light-controllable properties and analyzes its effects on liquid crystal cholesteric phases.

Findings

Reversible trans-cis isomerization under UV/VIS irradiation.

Concentration-dependent helical pitch in nematic liquid crystals.

Reversible isomerization at constant temperature.

Abstract

We present the newly synthesized chiral dopant 2-[(2-isopropyl-5-methylcyclohexyl)oxy]-2-oxoethyl 4-{(E)-[4-(decyloxy)phenyl]diazenyl}benzoate (ChD-3501), consisting of azo- and aliphatic fragments together with a chiral center based on l-menthol as a reversible light-controllable chiral dopant. To assess the effects of UV/VIS irradiation and temperature in the isotropic and liquid crystalline (LC) states, we studied the spectral kinetics of ethanol solution of ChD-3501, as well as induction of the cholesteric helix when it was dissolved in nematic LC (E7) as a chiral dopant. The concentration dependence of the helical pitch of the induced cholesterics was studied by means on Grandjean-Cano method, and the helical twisting power of ChD-3501 in the nematic host E7 was determined. The reversible trans-cis isomerization of chiral dopandt ChD-3501 in E7 under UV/VIS irradiation was studied, and it has been found that the storage of the cis-isomer at certain constant temperature also leads to the reversible isomerisation, which presents a certain interest for applications.