Influence of surfactant-based microheterogeneous fluids on aggregation of copper phthalocyanine tetrasulfonate

Electronic absorption spectroscopy was used to measure the molecular associ ation of copper phthalocyanine tetrasulfonate in micellar solutions, a micr oemulsion made with cationic surfactant, and homogeneous solvents. Analysis of absorbance versus concentration data using a multiple-aggregation model and non-linear regression analysis gave values of association constants, m olar absorptivities and estimates of average aggregation number. Microemuls ions and aqueous micellar solutions made with alkylammonium surfactants inh ibited aggregation, probably because of interactions between the phthalocya nine sulfonate groups and the cationic surfactant head groups at interfacia l surfaces. Similar aggregation behavior was observed previously in multipl e-bilayer films of cationic surfactants. Water and aqueous solutions contai ning tetraethylammonium bromide or anionic SDS micelles provide environment s facilitating extensive aggregation of (CuPcTS4-)-Pc-II. The major species are dimers in water and acetonitrile/water, but the formation of higher ag gregates is promoted by addition of SDS or TEAB. Aprotic organic solvents p rovide environments intermediate between these two extremes, giving relativ ely large aggregation numbers (i.e, five to seven) but smaller association constants than aqueous media not containing cationic surfactants. Copyright (C) 1999 John Wiley & Sons, Ltd.