The UV absorbance of various aromatic organic counterions has been investigated in the presence of ionic surfactant micelle. Addition of the cationic surfactant micelle to aqueous solutions of the aromatic organic salts induces a red shift of the adsorption spectra. It is proposed that the red shift is caused by cation-π interaction, which requires proper situation and distance between the surfactant's headgroup and the aromatic organic counterion. By measuring the adsorption of the surfactant and the aromatic organic counterions, it is discovered that different aromatic organic counterions adopt different configurations. This explanation is consistent with the NMR results.

Key words: SURFACTANTS, LAURYL SODIUM SULFATE, INTERACTIONS, BENZENECARBOXYLIC ACID P, POTASSIUM BIPHTHALATE, ULTRAVIOLET SPECTROPHOTOMETRY