Optical behaviour of photoimageable cholesteric liquid crystal cells with various novel chiral compounds

Abstract

In theory, both polarity and steric hindrance are basic factors which affect molecular interactions. To investigate the optical properties and steric structures of chiral compounds having different chiral moieties which affect the wavelength of light reflection in liquid crystal (LC) cells, a series of novel chiral compounds and azobenzene derivatives were synthesized. The liquid crystalline phases of the compounds were identified using small angle X‐ray diffraction, differential scanning calorimetry and polarizing optical microscopy. Cholesteric LC cells with various synthesized chiral dopants which selectively reflect visible light were first prepared, the photochemical switching behaviour of colours was then investigated, with special reference to the change in transmittance in cholesteric LC cells containing an azobenzene derivative as a photoisomerizable guest molecule. Reversible isomerization of azobenzene molecules occurred in the cholesteric systems, resulting in a depression of T _ChI and a shift of the selectively reflected wavelength. We discuss the photochemically driven change in the helical pitch of the cholesteric LCs with respect to structural effects involving the chiral moieties. Molecular interactions caused by the added dopants, reliability and stability of the photoisomerization, and UV irradiation effects on the cholesteric LC cells were also investigated. A real image was recorded through a mask on a cholesteric LC cell fabricated in this investigation.

Acknowledgements

The authors would like to thank the National Science Council (NSC) of the Republic of China (Taiwan) for financial support of this research under Contract No. NSC 92‐2216‐E006‐003.

Notes

^aWeight ratio ZLI‐2293: S811: chiral dopant.

^bMajor reflected wavelength, before and after UV irradiation.

^c T _ChI: clearing temperature from cholesteric to isotropic phase.