A practical guide to versatile photoalignment of azobenzenes
Yannick Folwill, Zouheir Zeitouny, Jasleen Lall, Hans Zappe
Abstract
Photoalignment refers to a technique for the definition of the orientation of liquid crystals using light. The approach is based on the use of materials that either absorb or trigger a chemical reaction with an anisotropy that depends on the polarisation of light. Azobenzenes are a well-established for aligning liquid crystals in research applications. Despite their popularity, only few details of the process are publicly available. We consider here the optimisation of the photoalignment process using the dichroic dye Brilliant Yellow. Its solubility in various solvents; the alignment quality as a function of exposure time and intensity; the influence of humidity at various stages; and the stability of the process in the presence of environmental light are investigated. Additionally, the dichroic dyes Congo Red and Chrysophenine are tested to increase the portfolio of available photoalignment materials.