New Memory Systems Constructed with Polyimide LB Films Having Azobenzene Pendant Groups: Behavior of In-Plane Anisotropic Photoisomerization, Photoinduced Optical Anisotropy, and Anisotropic Photofading

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Abstract
Polyamic acids functionalized by azobenzene units possessing p-methoxy (3a) and p-nitro (3b) subtituents as pendant groups were newly synthesized for photomemory materials. Langmuir-Blogdett (LB) films of polyimides 5a and 5b were prepared by “Precursor Method” via LB films of polyamic acid long alkyl amine salts 4a and 4b. FTIR transmission and RA spectroscopy revealed conformational change of the pendant azobenzene groups between polyamic acid and polyimide LB films. Three kinds of new photomemory systems were fabricated using the polyimide LB films. In the beginning, the polyimide LB film of 5a performed in-plane anisotropic trans-cis photoisomerization on irradiation of the linearly polarized light at 400 nm. The reversible change (erase) was achieved by irradiation at 500 nm. Second, reversible photoinduced optical anisotropic property was observed in this LB film of 5a, which was caused by the alternative polarized light at 400 nm and nonpolarized light at 500 nm. The anisotropic property was erased by irradiation of the nonpolarized light at 400 nm. The third example was in-plane anisotropic photofading in the LB film of 5b. After irradiation of the polarized argon ion laser to the LB film, decrease in absorption due to photo-bleaching of chromophore was observed selectively in the parallel plane to the incident polarization.