A STUDY OF HOMOLOGATION AND THE OCCURRENCE OF AN SA-SC-SA SEQUENCE OF PHASES IN THE 4-N-ALKOXY-3-FLUOROPHENYL 4-(5-N-ALKYL-2-THIENYL)BENZOATES

Seventeen esters, derived from 4-n-alkoxy-3-fluorophenols and 4-(5-n-alkyl-2-thienyl)benzoic acids, have been prepared and their liquid crystal transition temperatures determined by thermal optical microscopy. On cooling the isotropic liquid, the S(A)-S(C)-S(A) sequence of phases reported for the octyloxy-octyl and octyloxy-nonyl esters has been observed for certain other homologues, principally members of the 4-(5-n-nonyl-2-thienyl)benzoates. For these compounds, the temperature range of occurrence of the intermediate S(C) phase decreases as the length of the alkoxy chain increases (for the hexyloxy-nonyl to dodecyloxy-nonyl esters) and the S(C) phase is absent for the tetradecyloxy-nonyl homologue.