Odd-even effects in the optical properties of chiral triplet liquid crystals based on estradiol

Abstract

A series of bis ω-cyanobiphenylyloxyalkanoate esters of estradiol with variable spacers have been prepared as chiral triplet liquid crystals. The compounds show very broad cholesteric phases and are transformed into cholesteric glasses at room temperature. They exhibit a relatively weak odd-even effect with spacer length for their cholesteric-isotropic transition temperatures and the associated entropy changes. This weak odd-even effect probably results from the orientation of the ester linkages to the estradiol moiety. This causes the cyanobiphenyl groups to be poorly ordered with respect to one another, regardless of the odd or even number of methylene units in the alkanoate spacer. The selective reflection wavelength of the planar cholesteric phase of most of the compounds increases strongly with temperature and changes from blue at low temperature to red at high temperature. An odd-even effect of the selective reflection wavelength with spacer length as observed with other chiral twin and triplet liquid crystals is hardly observed.