2ND HARMONIC-GENERATION IN HEMICYANINE LANGMUIR-BLODGETT MONOLAYERS DEPOSITED FROM AQUEOUS SUBPHASE OF HALIDE SALT SOLUTION

Langmuir-Blodgett (LB) monolayers of hemicyanine dye were deposited onto glass substrates from aqueous subphase. The concentration of potassium iodide (KI) in the subphase was found to have a remarkable effect on both the isotherms and second harmonic generation (SHG) signals of the monolayers. SHG from mixed hemicyanine-arachidic acid LB monolayers prepared with and without KI in the subphase, and SHG from stilbazium salt (which has the same chromophore as hemicyanine except for substitution of the I- ion for Br- in the latter) LB monolayer were also carefully studied. The results of these experiments confirm that the I- ions in the subphase play an important role not only in disintegrating the formation of H aggregates in hemicyanine LB monolayers but also in increasing the monomeric hyperpolarizability beta as a result of changing the charge distributions in dye molecules.