Reentrant phenomenon in cyanoaryl alkylthioxybenzoates and cyanobenzoyloxyphenyl alkylthiobenzoates

Three new series of cyanoaryl 4-alkylthioxybenzoates have been synthesized and characterized. The 4-cyanophenyl series displays only transient mesomorphic properties while the 6-cyano-2-naphthyl and 4-cyanobiphenyl series exhibit the classical nematic and smectic A phases; a reentrant nematic phase is also found in the latter. Two other new series in which the position of the sulphur atom in the central rigid core has been varied were also prepared: The 4–[4′-cyanobenzoyloxy]-phenyl 4-alkylthiobenzoates and 4–[4′-alkylbenzoyloxy]phenyl 4-cyanothiobenzoates. As in the analogous benzoate series, the reentrant phenomenon with the sequence C, SAre, Nre, SA, N, I is observed with the nonyl derivatives. Comparisons between the alkoxybenzoates and the alkylthioxybenzoates are given. © 1990 Taylor & Francis Group, LLC.