in electro optical devices are described application_number US 52359474 A description wherein r is straight chain alkyl of 3 to 8 carbon atoms or straight chain alkoxy of 3 to 10 carbon atoms the compounds of formula i have in the liquid crystalline state a positive anisotropy of the dielectric constants i e u03b5 sub u2225 gt u03b5 sub wherein u03b5 sub u2225 is the dielectric constant along the longitudinal axis of the molecule and u03b5 sub is the dielectric constant perpendicular thereto in an electric field the nematic liquid crystals of the invention orientate themselves because u03b5 sub u2225 gt u03b5 sub in the direction of their largest dielectric constant that is with their longitudinal axis parallel to the direction of the field this effect is utilized inter alia in the interaction between embedded molecules and the liquid crystalline molecules guest host interaction described by j h helmeier and l a zanoni applied physics letters 13 91 1968 another interesting application of the dielectric field orientation is in the rotation cell discovered by m schadt and w helfrich applied physics letters 18 127 1971 as well as in the kerr cell described in molecular crystals and liquid crystals 17 355 1972 in the electro optical rotation cell there is present essentially a condenser with transparent electrodes whose.