Novel bent-shaped liquid crystalline compounds: III. Synthesis of Schiff base liquid crystal dimers

A group of new bent-shaped mesomorphic compounds with two identical mesogens (Schiff base), which have 2-hydroxy-1,3-dioxypropylene (–OCH2CH(OH)CH2O–) as a short spacer unit, and different lengths of terminal alkoxy chains (–OCnH2n+1; n = 5–10, 12), are synthesized. Transition temperatures and phase characterization were studied by DSC, POM and XRD analyses. The dependence of phase transition temperatures on the terminal alkoxy chain lengths is discussed. With the increase in the terminal chain lengths, the thermal stability of the smectic mesophases of these liquid crystals was increased, and the smectic–isotropic transition temperatures in this series showed an even–odd effect.