Adsorption-Induced Second Harmonic Generation from the Layer-by-Layer Deposited Ultrathin Film Based on the Charge-Transfer Interaction

This paper is concerned with the second harmonic generation (SHG) from as deposited layer-by-layer adsorbed films. A nanolayered film was fabricated through the intermolecular charge-transfer interaction between the electron-donating carbazole (Cz) group and electron-accepting 3,5-dinitrobenzoyl group in the side chains of methacrylate-based polymers. A nonlinear optical dye was introduced in the film by using the copolymer in which Cz and disperse red 1 (DR1) groups were attached to the side chains. The DR1 moiety was highly oriented through the adsorption of PCzEMA-DR1, and the orientation was relaxed by additional adsorption of the polymers onto the DR1-containing layer. The second harmonic (SH) intensity of the multilayered film remained almost constant for the layers of even and odd numbers. This behavior could be explained by considering the change in the nonlinear susceptibility of the succeeding DR1-containing layer. The SH intensity kept constant up to 120 °C for thermal stability.