ODD-EVEN EFFECTS IN THE THERMOTROPIC AND OPTICAL-PROPERTIES OF 3 SERIES OF CHIRAL TWIN LIQUID-CRYSTALS

Three series of novel chiral twin liquid crystals consisting of a chol esteryl and a 4'-cyanobiphenyl-4-yloxy group (III) or a 4-cyanophenoxy group (IV) and of a dihydrocholesreryl and a 4'-cyanobiphenyl-4-yloxy group (V) connected by an alkanoate spacer with a varying number (1-7 and 10) of methylene units were synthesized and their mesogenic prope rties investigated. Strong odd-even effects were observed as a functio n of spacer length for the phase transition temperatures, the correspo nding entropy changes and the selective reflection wavelengths associa ted with the chiral nematic phase. The compounds with an even number o f methylene units have a smaller pitch than the compounds with an odd number of methylene units. Replacement of the cholesteryl group by a d ihydrocholesteryl group results in an larger pitch, whereas replacemen t of the 4'-cyanobiphenyl-4-yloxy group by a 4-cyanophenoxy group give s a smaller pitch.