Effect of subphase divalent ions on optical second harmonic properties of hemicyanine Langmuir-Blodgett films interleaved with compatible spacer

The surface pressure-area (π-A) isotherms of 1.10-bistearyl-4.6.13.15-tetraene-8-nitrogen-crown-6 (NC) monolayers at the air-water interface, the UV-visible absorption spectra and optical nonlinear properties of Y-type hemicyanine/NC interleaving Langmuir-Blodgett (LB) multilayers containing divalent ions in the subphase (such as Cd2+, Ba2+ and Co2+) were investigated in the paper. It was found that the π-A isotherms of the NC monolayer, the peak position of absorption spectra and the optical second harmonic intensity in the alternating LB multilayers strongly depend on the divalent ions in the subphase. The 2ω resonance effect of molecular hyperpolarizability β was responsible for the change of the observed second order polarizability χ(2) of LB multilayers.