Mesomorphic Behavior of 4-t-Butylphenyl 4-(4-Alkoxybenzylideneamino)benzoates and 4-(4-Alkoxybenzylideneamino)phenyl4-t-Butylbenzoates

Phenyl 4-(4-alkoxybenzylideneamino)benzoates become more strongly smectogenic by the incorporation of the 4-t-butyl group to the phenyl moiety and only the methoxy member is purely nematogenic. The ethoxy to pentyloxy members exhibit both a nematic phase and a smectic A phase. The higher homologous members are no longer nematogenic and a smectic C phase is additionally generated. The t-butyl group gives a decrease in the nematic thermal stability by 26 to 6 degrees C relative to that of the unsubstituted phenyl esters depending upon the alkyl chain length. The mesomorphic properties of the 4-ethylphenyl and 4-isopropyl esters are presented for comparison. A smectic: C phase is observed for the hexyloxy and higher members of the latter ester. In contrast, the isomeric 4-(4-alkoxybenzylideneamino) phenyl 4-t-butylbenzoates produce no smectic: phase.