Synthesis and characterization of a novel polyimide-based second-order nonlinear optical material

A processable polyimide having azo-chromophore functionalized with cyanosulfonyl group (PI-SOT) was prepared for nonlinear optics applications. To introduce a highly nonlinear optical active chromophore on the polyimide matrix, we first synthesized monomers 4-[N,N-bis(hydroxyethyl)amino] -4'-(2,5-dioxolane)azobenzene (AZO-OH2) and 4,4'-(hexafluoroisopropylidene)diphthalimide (6F-DI). After the polymerization reaction between AZO-OH2 and 6F-DI by using the Mitsunobu reaction, the dioxolane group of the resulting polymer PI-PRO was deprotected from the polymer PI-DEP having aldehyde group, and this polymer was further reacted with methanesulfonylacetonitrile to produce the final polymer PI-SOT. The molecular weight of PI-SOT was determined to be M-n = 5650 (M-w/M-n = 1.4). From DSC and TGA thermograms a glass transition temperature of ca. 186 degrees C and an initial decomposition temperature of ca. 201 degrees C were observed. PI-SOT dissolved in cyclohexanone could be easily processed into high optical quality films. The optical nonlinearity was determined to be d(31) = 50 pm V-1 and d(33) similar or equal to 150 pm V-1 (nonresonant d(33)(infinity) value: 47 pm V-1)by the second harmonic generation method in in-situ condition at a fundamental wavelength of 1064 nm and its value showed good thermal stability up to 150 degrees C. By using the simple reflection measurement technique, a large electro-optic coefficient of r(33) = 28 pm V-1 at 633 nm wavelength was obtained. (C) 2000 Elsevier Science Ltd. All rights reserved.