Mesomorphism in the 4,4′-Dialkoxy-trans-Stilbenes

Abstract

In order to ascertain the effect of linkage groups (X[dbnd]Y) in mesomorphic substances of the general formula a homologus series of stilbenes has been prepared, where R[dbnd]C_n, H_2n+1O—, X[dbnd]Y[dbnd]CH. The lower members of the series (1 ≤ n ≤ 10) are monotropic nematic, while the higher members (12 ≤ n ≤ 16) are monotropic smectic substances. The mesophase-isotropic transition temperatures are higher than those reported for the related nitrones (X[dbnd]CH, Y[dbnd]N → O) and Schiff Bases (X[dbnd]CH, Y[dbnd]N). Also the entropies of the nematic-isotropic transitions, as measured by differential scanning calorimetry, are nearly the same in the stilbenes and the nitrones. These results suggest that the permanenet dipole associated with the linkage group plays a relatively unimportant role in enhancing the intermolecular attractions which are responsible for mesomorphic alignment.