Fluorosubstitution of the Molecular Core in Chiral Esters with Short Terminal Carbon Chains: Influence on Physical Properties

Comparative study of chiral liquid crystalline (S)-(1)-4’-(1-methylheptylcarbonyl) biphenyl-4-yl 4-[4-(2,2,3,3,4,4,4-heptafluorobutoxy)butyl-1-oxy] benzoate (4HH) and (S)-4’-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[4-(2,2,3,3,4,4,4-heptafluorobutoxy) butyl-1-oxy]-2,3-difluorobenzoate (4FF) is performed by complementary methods. For 4HH melting of the low-temperature crystal phase and subsequent cold crystallization (from antiferroelectric smectic CA* phase to the high-temperature crystal phase) are reported, crystallization kinetics is examined and a monotropic hexatic SmXA* phase is observed on cooling. For 4FF rich polymorphism in the solid state is investigated mainly by simultaneous X-ray diffraction and differential scanning calorimetry measurements. Influence of fluorosubstitution on structural, electro-optic and dielectric properties of the smectic phases is reported. Unit cell parameters of crystal phases of 4HH and 4FF are determined. The reported results show that the double fluorosubstitution slows down the Goldstone mode and PH phason in the smectic phases and facilitates crystallization.