Determination of CMC of Surfactants Using Polarity Sensitive Aryl Dye

A spectrophotometric method using a red absorbing aryl dye has been studied for the determination of critical micelle concentrations of surfactants. Cyanine dye related aryl dye compounds may be prepared by condensation of arylcarboxaldehydes with a quaternary salt of a heterocycle having a methyl group in the 2- or 4-position. These dyes have relatively longer absorption and fluorescence wavelengths than the aryl compound itself, allowing the researcher to utilize the lower interference of this region. In this paper one compound that belongs to the aryl dye family obtained by condensing 1-pyrenecarboxaldehyde with 3-ethyl-2-methylbenzothiazolium bromide was used as a hydrophobicity probe to detect formation of micelles. The chromophore has an absorption maximum at 564 nm in ethanol and at 619 nm in aqueous solutions. The analytical utility of these phenomena has been evaluated.