Tetracarboxylic dianhydride containing the second-order nonlinear optical chromophore thiophene-type stilbene with diethylamino and tricyanoethenyl substituents on each terminal was newly synthesized. Polyamic acid prepared from the tetracarboxylic dianhydride and N, N<sup>′</sup>-diaminodiphenyl ether was soluble in aprotic polar solvents and had an inherent viscosity of 0.2 dL/g. Polyimide obtained by heating of the polyamic acid at 160 °C was thermally stable to 240 °C. Polyimide Langmuir–Blodgett (LB) films were prepared by the precursor method through polyamic acid alkyl amine salts (the precursor of polyimide) with three kinds of alkyl amine. The precursor LB film had a Y-type structure and a good linear relationship between thickness and absorption at 650 nm in both precursor and polyimide LB films. Fourier-transform IR spectra before and after imidization indicated that the nonlinear optical chromophore remained in the polyimide LB film. It was found from the observation of transmission UV–visible spectra that the nonlinear optical chromophore was oriented more nearly perpendicularly in polyimide LB film than in the precursor LB film.
© 1998 Optical Society of America
Cheolsoo Jung, Mitsutoshi Jikei, and Masa-aki Kakimoto, "Synthesis of polyamic acid possessing second-order nonlinear optical properties and its application to Langmuir Blodgett films," J. Opt. Soc. Am. B 15, 471-476 (1998)