Antiphase Behavior in the 4-n-alkoxybiphenylyl-4′-cyanobenzoates (nOBCB's)

Abstract

Abstract A number of members of the 4-n-alkoxybiphenylyl-4′-cyanobenzoate (nOBCB) homologous series were prepared and found to exhibit smectic antiphase behavior. The early homologues (n-pentyloxy to n-heptyloxy) possess At phases while the higher members (n-octyloxy to n-dodecyloxy) show_Ad phases. At the n-octyl homologue a tilted C antiphase is introduced. The Ad to [Ctilde] phase change was shown to be strongly first order from differential scanning calorimetry. Later members of the series also exhibit smectic Cˇ phases on cooling the C phase, for example, the decyloxy compound exhibits an Ad, [Ctilde], C phase sequence on cooling. Miscibility studies between the early and later members show reentrant nematic phase behavior which occurs at the junction of the N-A1 and N-Ad transition temperature curves. The analogous materials, the 4-cyanophenyl 4′-n-alkoxybiphenyl-4-carboxylates do not exhibit antiphases and simply show N and A phases.