Liquid Crystals with Symmetrical Diamide Linkages

The Liquid Crystalline Compounds comprising of amide linkages are rare as it was believed that amide linkages are deterrent to mesomorphism. Our school has contributed significantly in synthesizing and evaluating the mesogenic properties of amide compounds (1,2,3). So far compounds with single amide linkage were studied and these were found to be thermally stable Liquid Crystals. In the present study attempt has been made to evaluate the mesogenic properties of compounds with two amido linkages. The two amide linkages will raise the solid-mesomorphic temperature very high, hence two lateral methoxy substituents were preferred on the biphenyl ring to depress the solid-mesomorphic temperatures. The first ever extensive series with diamide linkages behaves like a normal nematogenic series with wide range of mesomorphism. The lower members are nematic, the middle members exhibit polymesomorphism and the higher members exhibit only smectic mesophases. The series is thermally quite stable. The present work is compared with structurally related compounds to evaluate the salient features of the series. The smectic phases are characterized from the textures and by the contact method. The role of acoplanarity in reducing the mesogenic properties is evaluated by spectroscopic measurements of substituted and non-substituted biphenyl derivatives.