The influence of structural changes of the N-substituent on liquid crystalline behaviour of ester imides

Several new ester imide derivatives with different N-substituents in the imide ring were synthesized and their mesogenic properties investigated by thermal analysis, optical microscopy and X-ray diffraction. All the esters of N-4-[(4'-decyloxybiphenyl-4-yl)oxycarbonyl]phthalimideacetic acid and aliphatic alcohols exhibited monolayer SmA and SmC phases. In addition, for the ethyl and propyl esters a monotropic hexatic (F or I) phase was observed. The introduction of additional substituents at the carbon atom in the methylenemethoxycarbonyl group (in the vicinity of the nitrogen atom) substantially influenced liquid crystalline properties: the compounds with a flexible chain exhibited monotropic SmA-SmB dimorphism, but liquid crystalline properties vanished for the substituent containing the more rigid phenyl ring.