Influence of CTACl cationic micelles on the spectral behavior of crystal violet

In an aqueous medium, the absorption spectrum of UV-Vis of crystal violet decomposes in the sum of two Gaussians centered at 17,953 cm−1 (λ = 557 nm) and 16,807 cm−1 (λ = 595 nm). The addition of a surfactant, CTACl (hexadecyltrimethylammonium chloride), causes the appearance of a third Gaussian centered at 16,474 cm−1 (λ = 607 nm). The Gaussian centered at 16,474 cm−1 appears as a consequence of the formation of a new ionic pair structure between the crystal violet and the ion Cl− in the Stern layer of the micelle, at the same time that the areas of the Gaussians centered at 17,953 and 16,807 cm−1 decrease. On the basis of the areas of the constituent Gaussians, we can obtain the values of the association constants of the different structures of the fundamental state of the crystal violet in the CTACl micelles.