Unique Electro‐Optical Properties of Liquid Crystals Designed for Molecular Optics

• Published in: Advanced functional materials 2001-04, Vol.11 (2), p.87-94
• Main Authors: Lagerwall, S. T., Dahlgren, A., Jägemalm, P., Rudquist, P., D’havé, K., Pauwels, H., Dabrowski, R., Drzewinski, W.
• Format: Article
• Language: English
• Subjects: Antiferroelectricity; Liquid crystals, orthoconic; Liquid crystals, smectic; Molecular optics
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/1616-3028(200104)11:2<87::AID-ADFM87>3.0.CO;2-E

Antiferroelectric order has been known to exist in liquid crystals since more than a decade and is now an intensely studied field of research. The great application potential of antiferroelectric liquid crystals has especially been demonstrated in sophisticated flat‐panel display prototypes, which nevertheless have not yet reached manufacturing, due to the severe intrinsic problem of folds in the smectic layers, which drastically limit the achievable contrast, and which seem impossible to circumvent. By proper molecular design, we have developed and tested a new generic class of antiferroelectric materials that present an elegant solution to this problem. Their optical properties make them unique not only among liquid crystals but among electro‐optical materials in general. The design of this generic class, which we call orthoconic, also gives an illustrative example of the physical meaning of the addition of tensorial properties. Normal surface‐stabilized antiferroelectrics are optically positive biaxial crystals, with an effective optic axis along the smectic layer normal. The surprising optical property of the corresponding orthoconic antiferroelectric can be formulated as a theorem: When the tilt directions in adjacent smectic layers are made perpendicular to each other, the material becomes negatively uniaxial with the optic axis lying perpendicular to the smectic layer normal. The electro‐optic effect in such a material is based on the fact that the optic axis can be switched between three mutually orthogonal directions, corresponding to zero, negative, or positive values of the applied electric field. By proper molecular design, a new generic class of antiferroelectric materials have been developed and tested. Their optical properties make them unique not only among liquid crystals but among electro‐optical materials in general. The design of this generic class, which is called orthoconic, also gives an illustrative example of the physical meaning of the addition of tensorial properties (see Figure).