Monomolecular Photo-Alignment Layer for Liquid Crystal Alignment

In this article, we disclose a cinnamate-based compound that contains a phosphonic acid group, serving as a photoalignment layer for liquid crystals. The proposed alignment material demonstrates a strong affinity for various metal oxides due to the presence of phosphonic acid as an anchoring group. It can be applied to an ITO-coated glass substrate through a dip-coating technique, followed by a washing process. These photoalignment materials can form a monomolecular layer that demonstrates effective alignment when irradiated with polarized light. These materials are characterized by high anchoring energy, a high voltage holding ratio, and low residual direct current, offering both planar and vertical alignment of nematic liquid crystals depending on their molecular structure. This alignment technique is suitable for displays and other photonic devices that can be fabricated on flexible and solid substrates. Additionally, the dip-coating method simplifies the fabrication process by eliminating the complex and energy-intensive hard baking typically associated with conventional polyimides (PIs). As a result, this can significantly reduce fabrication costs and the carbon footprint for display production lines.