Fixation of Polar Assembly of Columnar Liquid Crystals with a Phosphine Oxide Group

We have developed a polar polymer film with a fixed polar assembly based on the phosphine oxide group. A polymerizable columnar liquid crystal with a polar triphenylphosphine oxide core was designed and synthesized. The in situ photopolymerization of the columnar liquid crystal under electric fields leads to fixation of a one-dimensional polar alignment of the phosphine oxide group. Fixation of the polarity of the cross-linked film was confirmed based on the results of second-harmonic generation measurements. In contrast, the polarity of the non-cross-linked triphenylphosphine oxide-based columnar liquid crystals was switchable under external electric fields. Moreover, it was not maintained after the removal of the electric fields. These findings have significant implications for potential applications in piezo-responsive devices and contribute to a broader understanding of polar liquid crystals and their prospective uses.