Orientation of functional groups in polyelectrolyte multilayers studied by second-harmonic generation (SHG)

The orientation of polymer bound, NLO-active dye disperse red in alternating polyelectrolyte multilayers was investigated by second harmonic generation. Film growth was followed by UV/Vis spectroscopy, and films were probed for internal order and roughness by small angle X-ray reflectivity. The orientation of the dyes was followed in-situ using Second Harmonic Generation (SHG). Some chromophore orientation was observed for most systems, which however, typically passes over a maximum with ongoing film growth. The intensity of the SHG could not be correlated with the molecular structure of the polymers employed. Surprisingly, heating/drying of certain films increased the SHG activity substantially. Attempts were made to increase and to stabilize the orientation of the chromophores by inclusion complexation with a charged cyclodextrin.