Synthesis of Some New Fluorene Esters with Mesomorphic Behavior

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Abstract
A number of 2-fluorenyl 4′-alkylbenzoates and 4′-alkoxybenzoates have been synthesized to study the effects of the central ester linkage on their mesomorphic behavior. These compounds typically show nematic (N) and the uniaxial smectic phases. Many isomeric fluorene esters with reversed ester linkage were also prepared, but no major differences were observed. The presence of a lateral substituent in the phenyl ring decreases the nematic-isotropic (N-I) temperature by about 28°C. Replacement of phenylene by trans-cyclohexylene has the unusual effect of increasing the N-I transition temperature by about 21°C. The presence of a nitro group at position (7) of the fluorene ring increases N-I temperature by about 66°C and stabilizes the SA.