Sequentially adsorbed electrostatic multilayers of branched side-chain polyelectrolytes bearing donor-acceptor type Azo chromophores

Two newly synthesized polyelectrolytes (PBANT-AC and PBACT-AC) functionalized with branched side chains bearing electron donor-acceptor type azobenzene chromophores were used as polyanions to build up multilayer films through an electrostatic sequential adsorption process by using poly(diallyldimethylammonium chloride) (PDAC) as the polycation. When dissolved in anhydrous DMF 14 and a series of DMF-H2O mixed solvents with different DMF to H2O ratios, both azo polyelectrolytes could form uniform multilayer films through the layer-by-layer adsorption process. Altering the water content of the dipping solutions of both azo polyelectrolytes was found to dramatically change the thickness of the sequentially adsorbed bilayers, chromophore orientation, and surface roughness of the multilayer films. On the other hand, the solvent effect on the H-aggregation in the multilayer films was determined by the structural details of the azo polyelectrolytes. After the irradiation with a linearly polarized Ar+ laser beam at 488 nm, significant dichroism was induced in the PBANT-AC/PDAC multilayer films prepared from the DMF dipping solution. Upon exposure to an interference pattern of Ar+ laser beam at modest intensities, optically induced surface modulation on the multilayer surfaces was observed.