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 po lyimide of high glass transition temperature (T-g approximate to 210 d egrees 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 nonlinea r optical chromophores induces, in turn, a movement of the polyimide m ain chain. This allows for an efficient orientation of the dye molecul es in spite of the stiffness of the polyimide main chain. A nonpolar o rientation is induced by polarized light irradiation alone, whereas po lar orientation is achieved by application of a de field during the ph otoisomerization process. Further light irradiation in the absence of a de field destroys the previously induced stable polar order. A detai led theoretical study of this light-induced depoling process is also p resented. (C) 1996 Optical Society of America.