Photoinduced surface alignment for liquid crystal displays

TLDR

Illuminating a liquid crystal alignment layer with polarized light induces surface anisotropy and a preferred in‑plane director orientation, while photochemical reactions can switch anchoring from homogeneous to homeotropic. This review examines surface alignment of liquid crystals by light exposure and discusses how cis/trans isomerization, crosslinking, and photodegradation can be employed to create photoalignment layers and optimize their performance. The authors describe pretilted alignment and introduce theoretical models to explain the photoalignment process, detailing how molecular design and light‑induced reactions produce the desired anchoring. The review presents a range of display and non‑display applications for photoalignment and demonstrates that cis/trans isomerization, crosslinking, and photodegradation can be used to produce layers with optimized performance.

Abstract

This review examines surface alignment of liquid crystals by exposure to light. 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 crystal 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 theoretical models are introduced to explain the photoalignment process. A range of display and non-display applications for photoalignment is presented.