Lipid-like hemicyanine Langmuir-Blodgett film characterized by second harmonic generation

A lipid-like hemicyanine molecule was synthesized and the Langmuir-Blodgett (LB) film was formed. The optical anisotropy of the LB film caused by film -forming process and the influence of the bulk pH value on the LB film when dipped in solution were investigated. From the experimental data and simul ation, it has been found that the lipid-like hemicyanine molecule on the LB film has at least four different forms at different pH values in solution. The surface pK(a) between these forms and the difference of pH value betwe en the surface and the bulk were derived: pK(a1) = 0.42, PKa2 = 5.11, pK(a3 ) = 12.40 and Delta pH = pH(s) - pH(b) = - 0.63. A surface potential of - 3 7.3 mV was derived from the simulation.