ABSTRACT
A dozen electrooptical effects in nematic liquid crystals (LC) connected with director reorientation of different types are known. In these cases, if the liquid crystalline materials contains a dichroic dye, the electrically induced LC director reorientation causes a simultaneous change in the orientation of the dye's long molecular axes and, therefore, the color of the electrooptical cell also changes. This phenomenon is utilized in the design of color displays. The polarizer is oriented in such a way that the polarization of the incident light is parallel to the LC director. Then, the electric field applied to the LC layer will rotate the director, thus changing the absorption of those dye molecules whose long axes form an angle less than 90° with the director. When one applies a voltage two to three times higher than the threshold one the director becomes homeotropic, thus lowering the absorption of the dye.
