The pendant dye attached to the polyamic acid backbone in the monolayer Langmuir film is directed toward the air side from the polymer main chain, so that the monolayer has a second-harmonic (SH) active C∞V symmetry where the symmetry axis is along the surface normal. The orientation is maintained in the monolayer Langmuir-Blodgett (LB) film obtained by vertical deposition. Since the counter ammonium ion with 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 imidization: the dye moieties collapse and lie along the surface in the polyimide monolayer LB film in the air. However, the dye moiety attached to polyimide maintains the SH-active C∞V symmetry in benzene solution, since the dye orientation is supported by the interaction with the solution.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Surfaces and Interfaces
- Surfaces, Coatings and Films
- Metals and Alloys
- Materials Chemistry