Light-induced orientation in a high glass transition temperature polyimide with polar azo dyes in the side chain

We report on both polar and nonpolar light-induced orientation of a polyimide of high glass transition temperature (T-g approximate to 210 degrees C) with nonlinear optical azo dye molecules in the side chain. This photoinduced orientation is shown to occur at room temperature, i.e., at least 190 degrees C below the T-g value of the polymer, which indicates that the photoisomerization-induced movement of the nonlinear optical chromophores induces, in turn, a movement of the polyimide main chain. This allows for an efficient orientation of the dye molecules in spite of the stiffness of the polyimide main chain. A nonpolar orientation is induced by polarized light irradiation alone, whereas polar orientation is achieved by application of a de field during the photoisomerization process. Further light irradiation in the absence of a de field destroys the previously induced stable polar order. A detailed theoretical study of this light-induced depoling process is also presented. (C) 1996 Optical Society of America.