Photo-induced Inversion of the Cholesteric Helix in Systems Containing 3(R)-Methylcyclohexanone 6-Arylidene Derivatives

Abstract

Induced cholesteric systems which were based on 4-pentyl-4′-cyanobiphenyl and contained 3(R)-methylcyclohexanone 6-arylidene derivatives as chiral dopants showed the helix inversion under UV light exposure due to the effective E-Z photoisomerization of the dopant. Rather high twist extent produced during this process remained invariable under the subsequent irradiation or at elevated temperatures. The effect observed was driven by the sign and value difference in helical twisting powers of E- and Z-isomers of 3(R)-methylcyclohexanone derivatives. The cholesteric mixtures containing Z-isomers of 3(R)-methylcyclohexanone derivatives exhibited the selective visible light reflection.

Keywords:

• α,β-unsaturated ketones
• chiral dopants
• E-Z-isomerization
• helix inversion
• induced cholesteric
• liquid crystals
• selective visible light reflection

Acknowledgments

The authors are thankful to Drs. S. V. Iksanova, V. V. Vashchenko and Mr. O. V. Boryak for measurements of ¹H NMR, mass-spectra, and for the HPLC analyses supply.

Notes

^a Estimated by using Eq. (4)

^b Estimated by using Eq. (2)

^c Estimated by using Eq. (3)