Nonlinear optical properties of a processable polyimide having azo-dye functionalized with cyanosulfonyl group

A processable polyimide having azo-chromophore functionalized with cyanosulfonyl group (PI-SOT) was prepared for the nonlinear optics applications. The molecular weight of PI-SOT was determined to be Mn=5 650 (Mw/Mn=1.4). From differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) thermograms, it was observed that a glass transition temperature of ca. 186°C and an initial decomposition temperature of ca. 201°C. PI-SOT dissolved in cyclohexanone could be easily processed into high optical quality films. The optical nonlinearity was determined to be d33=150 pm V−1 (nonresonant d33(∞) value: 47 pm V−1) by the second harmonic generation method in in situ condition. By using the simple reflection measurement technique, a large electro–optic coefficient of r33=28 pm V−1 at 633 nm wavelength (5.4 pm V−1 at 852 nm) was obtained and its value showed a good thermal stability up to 150°C.