Control of Thermally Enhanced Photoinduced Reorientation of Polymethacrylate Films with 4-Methoxyazobenzene Side Groups by Irradiating with 365 and 633 nm Light and Annealing

Abstract

This paper describes two different techniques for thermally enhanced photoinduced reorientation of liquid crystalline polymethacrylate (PLC) films that contain 4-methoxyazobenzene side groups with various alkylene spacer lengths. One is the classical method based on photoselection and rotational diffusion in the steady state of the E/Z photoisomerization, which includes irradiating with linearly polarized (LP) 365 nm light and subsequently annealing in the liquid crystalline (LC) temperature range of the film. The spacer length and exposure dose significantly influence the reorientation direction. In-plane reorientation perpendicular to the electric vector (E) of the LP 365 nm light was generated for PLCs with short spacers, but out-of-plane reorientation with a small degree of in-plane reorientation was predominant for PLCs with long spacers. The other is an alternative technique based on an axis-selective Z-to-E photoisomerization using LP 633 nm light and thermally enhanced molecular reorientation. Regardless of the spacer length, a high order of in-plane reorientation parallel to E of LP 633 nm light was accomplished. Polarization UV−vis spectroscopy was used to investigate these reorientational behaviors and to clarify the mechanism.