ADSORPTION OF CYANINE DYES AND OPTICAL-PROPERTIES OF PHOSPHATIDIC-ACID LANGMUIR MONOLAYERS AND LANGMUIR-BLODGETT-FILMS

The optical properties and the aggregate structure are investigated for phosphatidic acid (PA) Langmuir films adsorbing cyanine dyes from the aqueous solution to the air-water interface and for PA Langmuir-Blodgett (LB) films containing the dyes on glass substrates. H* aggregation of the dyes oriented perpendicularly to the water surface is observed for the PA Langmuir films for subphases at pH 5. The H* aggregate, however, is not observed after the LB films are deposited onto the substrates, and J aggregates appear instead. Aggregate properties of the dyes in the PA Langmuir films and the LB films depend on the pH of the subphase and are different from those of the dyes adsorbed in arachidic acid (C20) films. Furthermore, absorption peaks of the aggregate models, calculated using the extended dipole model, coincide with the experimental absorption spectra. The properties are of great interest for controlling the characteristics of LB films adsorbing dyes and fabricating LB devices.