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Synthesis and mesomorphic properties of some fluorinated phenyl 4-[(4-n-alkoxyphenyl)ethynyl]benzoates

Eight homologous series of fluorinated phenyl 4-[(4-n-alkoxyphenyl)ethynyl]benzoates have been synthesized. Textural observations by polarizing microscopy and DSC measurements of the phase transitions show that most of these compounds are thermotropic liquid crystals with nematic and smectic A phases; furthermore, several show monotropic high order smectic phases. The results showed that the SmA phase is enhanced with increasing degree of fluorosubstitution on the para- and meta-positions of the terminal phenyl groups. The mesomorphic properties of these compounds are also affected by the direction of ester bonds. The effect of triple bonds is also discussed.