VARIOUS ORIENTATIONS OF PENDANT DYE ATTACHED TO POLYAMIC ACID LANGMUIR AND LANGMUIR-BLODGETT-FILMS STUDIED BY AN OPTICAL 2ND-HARMONIC GENERATION INTERFEROMETRY TECHNIQUE

The pendant dye attached to the polyamic acid backbone in the monolaye r Langmuir film is directed toward the air side from the polymer main chain, so that the monolayer has a second-harmonic (SH) active C(infin ityV) symmetry where the symmetry axis is along the surface normal. Th e orientation is maintained in the monolayer Langmuir-Blodgett (LB) fi lm obtained by vertical deposition. Since the counter ammonium ion wit h long alkyl chain functions as a pillar to support the dye moieties, the structure is changed owing to the removal of the counter ion by im idization: the dye moieties collapse and lie along the surface in the polyimide monolayer LB film in the air. However, the dye moiety attach ed to polyimide maintains the SH-active C(infinityV) symmetry in benze ne solution, since the dye orientation is supported by the interaction with the solution.