Synthesis, thermal and optical behaviour of non-symmetric liquid crystal dimers alpha-(4-benzylidene-substituted-aniline-4 '-oxy)-omega-[pentyl-4-(4 '-phenyl)benzoateoxy]hexane

A series of six non-symmetric liquid crystal dimers -(4-benzylidene-substituted-aniline-4'-oxy)--[pentyl-4-(4'-phenyl)benzoateoxy]hexane have been synthesized and characterized. These dimers vary from one another in terms of the terminal substituent (H, CH3, C2H5, F, Cl and Br) with different polarizabilities and molecular sizes. Investigation on the thermal behaviour shows that the dimer with a more polarizable terminal substituent of Br atom exhibits a smectic A phase as well as an enantiotropic nematic phase. Influence of the molecular size of the terminal substituent in stabilizing the liquid crystalline properties is also studied.