SPECTRAL PROPERTIES OF AGGREGATES IN ADSORBED DYE MONOLAYER FILMS

Adsorbed dye monolayer films are prepared by the complexation of a cya nine dye dissolved in the aqueous subphase to stearic acid (SA), oleic acid (OA) and dihexadecyl phosphate (DHP) monolayers at the air-water interface. Using UV-Vis spectroscopy, a wide range of aggregation beh aviour of the dye was observed with variation of the subphase pH and p re-treatment of the quartz substrate onto which the monolayers were tr ansferred from the water surface. The dye complexed to a 1:1 molar mix ture of SA and OA showed both monomer and J-aggregate on a hydrophobic substrate and only monomer when transferred onto a hydrophilic substr ate. For the DHP/dye monolayers, changing the subphase pH and the surf ace pressure at transfer yielded differing amounts of monomer and aggr egate, with the greatest amount of aggregate being obtained when trans ferring from the condensed phase. Furthermore, two different types of J-aggregate for the DHP/dye systems were observed depending upon the s ubstrate pre-treatment. (C) 1997 Elsevier Science S.A.