Influence of the rigidity of the steroid core in the structure of chiral dopants on the temperature dependence of cholesteric short pitch

• Dopants are derivatives of industrially available steroid and their synthesis is simple.
• Dopants own high twisting power and weak temperature shift of reflective wavelength.
• Low concentrations of dopant in nematic are needed to obtain red, green and blue colors.
• Good solubility of dopants in nematics provides the stability of reflected colors in time.

New chiral compounds of the steroid type, namely, 3-alkanoyl- and 3-alkyl derivatives of 16-arylidene estrone, were synthesized and exhibited high helical twisting power (HTP) in nematic liquid crystals E63 and LC-1289. The peculiarities of the molecular structure of chiral compounds (CCs) and their high degree of chirality were discussed. Quite small concentrations of chiral compounds in both nematic solvents were needed to obtain a short-pitch cholesteric helical macrostructure with the selective light reflection in the visible range of the spectrum. The insignificant temperature dependence of the maximum wavelength of the selective light reflection obtained on the whole cholesteric range for all studied liquid crystalline (LC) systems could be related to relatively rigid molecular structure of the chiral compounds. The cholesteric LC mixtures comprising 3-alkanoyl- and 3-alkyl derivatives of 16-arylidene estrone were characterized by the phase stability and the stability of reflective characteristics in time that makes it possible to consider this series of dopants as appropriate for development of bistable cholesteric reflective LC displays.

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