Unique electro-optical properties of liquid crystals designed for molecular optics

Antiferroelectric order has been known to exist in liquid crystals since mo re than a decade and is now an intensely studied field of research. Tile gr eat application potential Of antiferroelectric liquid crystals has especial ly been demonstrated in sophisticated flat-panel display prototypes, which nevertheless have not yet reached manufacturing, due to the severe intrinsi c problem of folds in the smectic layers, which drastically limit the achie vable contrast, and which seem impossible to circumvent. By proper molecula r design, we have developed and tested a new generic class of antiferroelec tric materials that present an elegant solution to this problem. Their opti cal properties make them unique not only among liquid crystals but among el ectro-optical materials in general. The design of this generic class, which we call orthoconic, also gives an illustrative example of the physical mea ning of the addition of tensorial properties. Normal surface-stabilized ant iferroelectrics are optically positive biaxial crystals, with an effective optic asis along the smectic layer normal. The surprising optical property of the corresponding orthoconic antiferroelectric can be formulated as a th eorem: When the tilt directions in adjacent smectic layers are made perpend icular to each other; rite material becomes negatively uniaxial with the op tic axis lying perpendicular to the smectic layer normal. The electro-optic effect in arch a material is based on the fact that the optic axis can be switched between three mutually orthogonal directions, corresponding to zer o, negative, or positive values of the applied electric field.