FLUORESCENCE POLARIZATION METHOD FOR STUDYING MOLECULAR-ORIENTATION OF MONOLAYERED AND MULTILAYERED POLYIMIDE FILMS PREPARED BY THE LANGMUIR-BLODGETT TECHNIQUE

Molecular orientation of mono- and multilayered polyimide films has been studied by the fluorescence polarization method. The high sensitivity of the fluorescence method enabled us to measure the orientation of extremely thin films. A perylene pigment was synthesized as a fluorescence probe and was introduced into polyamic acid chains. Layered films of polyamic acid alkylamine salt were prepared by the Langmuir-Blodgett (LB) technique. Even after chemical conversion to polyimide, molecular axes of the polyimide chain retained a 2-dimensional distribution in the substrate plane. The perylene probes in the LB film showed fluorescence anisotropy, and their second moment of orientation, (cos2-omega), was determined to be 0.54-0.58 by 2-dimensional analysis. The principal axis of the orientation was in agreement with the dipping direction. These measurements reveal the orientation of a "genuine surface" of molecular dimension. This LB polyimide surface aligns highly liquid-crystal molecules as a rubbed surface of polyimide film does. The ability of LB films to orient a liquid crystal correlated with the surface orientation measured by the fluorescence method.