Investigations of the process of photoinduced isomerization on azobenzene

A photochromism-testing system for azo dyes which has the characteristics of visualization, real-time and high accuracy was established. Photochromism process of methyl red (MR) solution and MR/polymethyl methacrylate (PMMA) film were studied. It was found that the effect of strengthening laser energy is similar to that of prolonging the excitation time, and the photochromism process of MR depends on steric hindrance around azobenzene molecule. There actually are two parts in photochromism due to photo-induced isomerization of azobenzene: a fast one mainly accompanied by photo-induced isomerization and a slow one in which azobenzene molecules parallel laser polarization direction and the oriented state can remain a long time in the MR/PMMA film.