Stability of azobenzene-containing polyimide film to UV light

We have investigated the stability of an azobenzene-containing polyimide (Azo-Pl) film with anisotropic molecular orientation to linearly polarized light (LP-L) of wavelength 340-500 nrn. The anisotropic molecular orientation was induced by exposing the corresponding polyamic acid film to LP-L of 72 J/cm(2), and then the film was thermally imidized. No significant change was observed in the in-plane molecular order of the Azo-Pl film over prolonged light exposure of 468 J/cm(2), but a 10% decrease of the number of the Azo-Pl backbone structure was observed. From these results we found that: (i) the reorientation of the backbone structure through photo-isomerization cycles of azobenzene is inhibited in the Azo-Pl film; (ii) the photo-decomposition of the Azo-Pl film proceeds with about 2 times the rate for a poly[4,4'-oxydiphenylenepyromellitimide] film.