Dielectric Properties of Liquid Crystalline Isothiocyanato-tolane Derivatives with Fluorine Atom at Various Lateral Positions

Dielectric studies were performed for several isothiocyanato-tolane compounds having the F atom attached to the benzene rings at different lateral positions and the alkoxy or alkyl chain at the p-position. They form the nematic phase in broad temperature intervals. The static as well as dynamic properties of the compounds in the nematic and isotropic phases were studied. Tensor permittivity components: ε‖, ε⊥, ∆ε, as functions of temperature were measured. The complex dielectric permittivity, ε∗(f) = ε′(f)−iε′′(f), was measured in the frequency range of 1 kHz – 3 GHz from which the relaxation times τ‖ and τ⊥ were calculated. The order parameter S(T ) was determined from the dielectric data. It was found that the close vicinity of the F atom and the alkoxy group results in blocking of the internal rotation of the wing around the O-phenyl bond.