EFFECT OF THE POSITION OF LATERAL FLUORO SUBSTITUENTS ON THE PHASE-BEHAVIOR AND FERROELECTRIC PROPERTIES OF CHIRAL 1-METHYLHEPTYL 4'-[(2-FLUORO-4-TETRADECYLOXPHENYL)PROPIOLOYLOXY]BIPHENYL-4-CARBOXYLATES OR 3-FLUORO-4-TETRADECYLOXYPHENYL)PROPIOLOYLOXY]BIPHENYL-4-CARBOXYLATES

The syntheses of four chiral laterally fluoro-substituted propiolate esters are described, along with transition temperatures, ferroelectric properties, phase diagrams and related data. The position of the fluoro-substituent was found to influence dramatically the formation of twist grain boundary (TGB A* and TGB C*) phases as well as the magnitudes of spontaneous polarization and optical tilt angle in the ferroelectric smectic C* mesophases. Differential scanning calorimetric studies revealed the presence of a diffuse liquid-liquid transition above the clearing point in both of the 3-fluoro enantiomers, but not in the racemate. Circular dichroism and optical rotation measurements, carried out over a temperature range in which the diffuse peak occurs, appear to confirm the presence of a degree of chiral organization within the isotropic liquid. It is suggested that this phenomenon may be due to the presence of cybotactic groups or a network of entangled screw dislocations occurring close to the clearing point.