Abstract
Cyanine (Cy) dye was embedded in (or absorbed by) an arachidic acid monolayer on an air-water interface and multilayer samples deposited on glass slides were obtained. The studies of their absorption spectra showed that Cy in Langmuir-Blodgett (LB) films formed H aggregates. The enhanced large third-order susceptibility has been measured to be 5 × 10 -8 e.s.u. for the LB films, which is three orders of magnitude larger than that deduced from the measured second-order hyperpolarizability of Cy monomers in bulk solution. The origin of this large third-order susceptibility for the LB films, due to the near-reaonant effect and indirect transformation between H aggregate and monomers and delocalized exciton enhancement in the aggregates, has been discussed as well.
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