Synthesis and characterization of novel fluorinated diphenyldiacetylenic liquid crystals

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Abstract
Five series of asymmetric diphenyldiacetylenes containing a single fluorine, two fluorines or a trifluoromethyl group at one end and an alkyl, alkyloxy or alkenyloxy group on the other end, were prepared and characterized. Most of the 4-alkylphenyl-4′-fluorophenyldiacetylenes, 4-alkyloxyphenyl-4′-fluorophenyldiacetylenes and 4-alkenyloxyphenyl-4′-fluorophenyldiacetylenes obtained exhibit an enantiotropic nematic phase and no smectic phase. However, most of the 4-alkyl-3′, 4′-difluorodiphenyldiacetylenes, 4-alkenyloxy-3′,4′-difluorodiphenyldiacetylenes and 4-alkyl-4′-trifluoromethyldiphenyldiacetylenes show no mesomorphic behaviour. The effects of alkyl, alkyloxy, alkenyloxy, fluoro, 3,4-difluoro and trifluoromethyl end groups on the mesomorphic behaviour of the diphenyldiacetylenes prepared are discussed.