Factors Affecting In-Plane and Out-of-Plane Photoorientation of Azobenzene Side Chains Attached to Liquid Crystalline Polymers Induced by Irradiation with Linearly Polarized Light

Photoinduced orientational behavior of polymethacrylates with side chains (amorphous polymers, pMAz2 and C2MeO, and liquid crystalline polymers, C6MeO and C12MeO) with different alkylene spacer lengths ( n = 2, 6, 12) were investigated by means of polarized Fourier transform infrared (FT-IR) and UV−vis absorption spectroscopy. Being different from pMAz2, C2MeO showed high optical anisotropy due to in-plane orientation and the excellent thermostability even above T g, which can be explained in terms of potential liquid crystallinity to be able to have a tendency to form a well-ordered domain. We observed marked dependence of photoorientation processes on film temperatures of C6MeO. While in-plane orientation was generated in glassy state as well as at 76 °C, irradiation at 90 °C slightly lower than T SN (transition temperature between smectic and nematic phases) gave rise to the distinct transformation from in-plane orientation at the early stage to successive out-of-plane reorientation, which was accompanied by H-aggregation. This situation enabled ones to record optical images in a C6MeO film on the basis of the difference in birefringences between two orientational modes. The biaxial reorientation occurred also for C12MeO, though both in-plane and out-of-plane photoorientation occurred simultaneously at room temperature as well as elevated film temperatures.