Correlation between polymer architecture and sub-glass-transition-temperature light-induced molecular movement in azo-polyimide polymers: influence on linear and second- and third-order nonlinear optical processes

We report on light-induced linear and second- and third-order nonlinear optical effects in high-glass-transition-temperature (Tg) photosensitive nonlinear optical azo polyimides. We present evidence of light-induced orientation of azo chromophores at room temperature in very high-Tg polyimides (Tg up to 350 °C) even though the chromophore is firmly embedded into the polymer backbone. We show that the isomerization reaction and the light-induced polar and nonpolar orientation depend on the molecular structure of the unit building blocks of the polymer. The mechanism of the photoassisted poling process is clarified, and it is shown how the linear and second- and third-order nonlinear optical effects can be controlled by light.