Azo Polymer Multilayer Films by Electrostatic Self-Assembly and Layer-by-Layer Post Azo Functionalization

This work focuses on the development of a novel method for molecular level assembly and processing of multilayer azo polymer films. Poly(acrylic acid)-based precursor anilino-functional polymer was first synthesized and used as a polyanion. This polymer was assembled into mono- and multilayer thin films by an electrostatic layer-by-layer deposition technique in conjunction with a polycation. The aniline group in the assembled polymer layer was subsequently converted to an azobenzene chromophore by post azo coupling reaction with appropriate diazonium salts. This method provides easy control of film thickness and well-ordered chromophore structure in the multilayer. Second harmonic generation was observed in all multilayer films, indicating acentric organization of the chromophores synthesized in the multilayered films. The second harmonic intensity and film thickness are dependent on the assembly conditions (pH, etc.) of the polyions. The post-functionalized azo polymer layers were further modulated by light-driven mass transport.