Light-induced orientation in azo-polyimide polymers 325 °C below the glass transition temperature

We report on light-induced nonpolar orientation of sidechain nonlinear-optical polyimides [glass transition temperatures (Tg) up to 350 °C] containing no flexible connectors or tethers. The nonlinear-optical azo-dye chromophore is incorporated through the donor substituent as a part of the polymer backbone. This impressive photoinduced orientation occurs at room temperature, i.e., at least 325 °C below the Tg of one of the polymers that we investigated. Furthermore, it is shown that, after photoinduced ordering, this polymer must be heated to 350 °C to induce main-chain movement and to erase the orientation, whereas the direction of orientation of the chromophores can easily be controlled at room temperature simply by choice of the appropriate polarization of the irradiating light. This light-induced orientation process is shown to be useful for storing images in waveguides.