PRINCIPAL COMPONENT ANALYSIS OF THE ABSORPTION-SPECTRA OF THE DYE THIACYANINE IN THE PRESENCE OF THE SURFACTANT AOT - PRECISE IDENTIFICATION OF THE DYE-SURFACTANT AGGREGATES

Spectral change of a cationic dye 3,3'-diethylthiacyanine iodide (THIA ) in the presence of an anionic surfactant AOT has been presented. The THIA-AOT system exhibits blue-shifted metachromasia at AOT concentrat ions below its critical micellar concentration (CMC) and is thought to be due to the aggregation of electrostatically bound dye-AOT complex (DS). Metachromasia is gradually reversed to the monomeric band (peak at 425 nm) by AOT above its CMC. Principal component analysis (PCA) me thod has been applied for spectral analysis; the results show that the metachromatic peaks at 377 and 366 nm originate, respectively, from t rimer and hexamer of the dye associated with AOT. From PCA, the molar absorption coefficient spectra of the individual absorbing components and the equilibrium constants for the systems, monomer reversible arro w trimer and hexamer reversible arrow monomer below and above CMC of A OT, respectively, have also been obtained. The micellar aggregation nu mber of AOT obtained from PCA is found to be 16 which is in good agree ment with the literature value. (C) 1997 Academic Press.