Non-symmetric chiral liquid crystal dimers. Preparation and characterisation of the (S)-(benzylidene-4′-substitutedaniline)-2″-methylbutyl-4‴-(4″″-phenyloxy)-benzoateoxy)hexanoates

The properties of six chiral non-symmetric dimers belonging to the family of (S)-(benzylidene-4′-substitutedaniline)-2″-methylbutyl-4‴-(4″″-phenyloxy)benzoate-oxy)hexanoates are described. The terminal substituents on the 4-benzylidene-4′-substituted fragment are H, Cl, Br, I, CH3 and C2H5. All six dimers exhibit an enantiotropic chiral nematic phase. The relationship between the chiral nematic-isotropic transition temperature and the terminal substituent is discussed in terms of the size of the substituent and its effect of the molecular shape, and its ability to interact with mesogenic group to which it is attached. The C2H5-substituted dimer also shows an enantiotropic monolayer chiral smectic C phase, the formation of which is attributed to the enhanced molecular inhomogeneity arising from the longer alkyl chain. The weak smectic tendencies seen for the halogen-substituted dimers are attributed to potentially repulsive interactions between the ester links that would occur in an intercalated smectic arrangement which would be expected for dimers of this type.