Fluorene Analogues of Biphenyls: Comparison of Mesogenic Behaviour

Abstract

A variety of 2, 7-disubstituted fluorenes has been synthesised including 2-alkyl-7-cyanofluorenes, 2-pentyl-7-fluorenyl esters and esters of 7-pentyl-2-fluorenecarboxylic acid. Transition temperatures have been determined and are compared with those of analogous biphenyl compounds: it is found that the melting points are higher and the nematic clearing points slightly lower than those of the biphenyl analogues. Suitable mixtures have been used to determine other physical properties. All of the fluorene esters prepared have a phenyl or cyclohexane ring incorporated in the structure to promote wide mesophase temperature ranges and higher melting points. Some of the esters also give smectic phases.