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

ABSTRACT

We present the synthesised 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 centre 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 isomerisation of chiral dopant 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. Possible applications of the studied system are discussed.

Graphical Abstract

KEYWORDS:

• Chiral dopant
• cholesteric liquid crystals
• helical twisting power (HTP)
• l-menthol
• azo-fragment
• reversible photoisomerisation
• trans-cis isomerisation

Acknowledgments

The authors thank W Becker (Merck, Darmstadt, Germany) for his generous gift of nematic liquid crystals E7, A Kratz (Merck, Germany) for her produce of the Licristal brochure and field service specialist IV V Danylyuk (Dish LLC, USA) for his gift of some Laboratory equipments. The authors thank Prof. A Tolmachev (Chemico-Biological Center Taras Shevchenko National University of Kyiv), Dr. S Minenko (Institute for Scintillation Materials of STC “Institute for Single Crystals” of the NAS of Ukraine) and Dr. S Lukyanets (Institute of Physics of the NAS of Ukraine) for the helpful discussions.

Disclosure statement

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