Photoinduced surface alignment for liquid crystal displays

This review examines surface alignment of liquid crystals by exposure to li ght. Two distinct effects are discussed: illumination with polarized light induces a surface anisotropy to an alignment layer and hence a preferred in -plane orientation of the overlying liquid crystal director. Alternatively, a photochemical reaction of the alignment surface changes the liquid cryst al anchoring conditions from homogeneous to homeotropic. We discuss how cis /trans isomerization, crosslinking and photodegradation are used to produce photoalignment layers and we show how the performance of the materials can be optimized by molecular design. Pretilted alignment is discussed and the oretical models are introduced to explain the photoalignment process. A ran ge of display and non-display applications for photoalignment is presented.