Dye–Surfactant Interaction: Role of an Alkyl Chain in the Localization of Styrylpyridinium Dyes in a Hydrophobic Force Field of a Cationic Surfactant (CTAB)

The interaction of a number of cationic dyes (I) with a varying number of methylene groups (Cn) in the alkyl chain attached to pyridyl nitrogen with a cationic surfactant (CTAB) assembly is reported. The binding constant of the dyes (C5 to C18) with the micelle have been calculated, and are found to increase with increasing carbon chain. A plot of the binding constant vs. the chain length shows a curve with a maximum for C16, which is attributed to a compatibility factor. From studies of the electronic and emission spectra it is proposed that a micelle has a hydrophobic force field and that the dyes are localized in various pockets of the field.