Polyelectrolyte Multilayer Assemblies Containing Nonlinear Optical Dyes

An ionene-type polycation incorporating a nonlinear optical chromophore was synthesized. It was employed for the assembly of alternating polyelectrolyte multilayers on charged and uncharged substrates, using different organic polyanions as well as montmorillonite clay as anionic counterparts. The assembly process was followed by UV/vis spectroscopy. The influences of the choice of anionic species and of variations in the layer architecture were studied. Different kinds of aggregation were observed for different species of polyanions employed, and the increase of absorbance with the number of layers proved to be dependent on the specific multilayer composition. The degree of orientation of the chromophores was investigated by second-harmonic generation and the nonlinear response was found to depend strongly on the anionic species. This result demonstrates that polyelectrolyte multilayers do not necessarily have a centrosymmetric structure, as generally assumed.