EFFECT OF THE POSITION OF LATERAL FLUORO SUBSTITUENTS ON THE PHASE-BEHAVIOR AND FERROELECTRIC PROPERTIES OF CHIRAL 1-METHYLHEPTYL ECYLOXPHENYL)PROPIOLOYLOXY]BIPHENYL-4-CARBOXYLATES OR CYLOXYPHENYL)PROPIOLOYLOXY]BIPHENYL-4-CARBOXYLATES

The syntheses of four chiral laterally fluoro-substituted propiolate e sters are described, along with transition temperatures, ferroelectric properties, phase diagrams and related data. The position of the fluo ro-substituent was found to influence dramatically the formation of tw ist grain boundary (TGB A and TGB C*) phases as well as the magnitude s of spontaneous polarization and optical tilt angle in the ferroelect ric 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 rac emate. Circular dichroism and optical rotation measurements, carried o ut over a temperature range in which the diffuse peak occurs, appear t o confirm the presence of a degree of chiral organization within the i sotropic liquid. It is suggested that this phenomenon may be due to th e presence of cybotactic groups or a network of entangled screw disloc ations occurring close to the clearing point.