INFLUENCE OF SPACER LENGTHS ON THE PROPERTIES OF CHIRAL TRIPLET LIQUID-CRYSTALS BASED ON ESTRADIOL

A series of 3-[omega-(4-cyanobiphenyl-4'-yloxy)alkyl] ethers of estrad iol 17-[omega-(4-cyanobiphenyl-4'-yloxy)alkanoates] with variable spac ers has been prepared as chiral triplet liquid crystals. The compounds show very broad range cholesteric phases and are transformed into cho lesteric glasses at room temperature. They exhibit odd-even effects fo r their cholesteric-isotropic transition temperatures and the associat ed entropy changes as a function of spacer length. The odd-even effect s are observed upon changing the parity of both the ester and of the e ther spacer. The best ordering is observed for compounds with an even number of methylene groups both in the ester and the ether spacer. In these cases the three mesogen units are oriented more or less parallel when the alkyl spacers are in the all-trans-conformations. Odd-even e ffects are also observed for the selective reflection wavelength of th e planar cholesteric phase, depending on the parity of both spacers. F or several compounds with short spacers the selective reflection wavel ength increases strongly with temperature, whereas for other compounds this is almost temperature independent.