Spectroscopic studies of interaction of Safranine T with nonionic micelles and mixed micelles

The visible spectra of Safranine T (ST) in micellar solution of Brij 58, Tween 20 and Tween 40 and mixed micellar solution of Brij 58/Tween 20 and Brij 58/Tween 40 indicate formation of 1:1 charge transfer (CT) complex between acceptor ST and donor nonionic micelles and mixed micelles. The experimental CT transition energies are well correlated (through Mulliken's equation) with the vertical ionization potential of the donors. The solvent parameters, i.e. the intramolecular charge transfer energy ET(30) have been determined from the Stokes spectral shift. Variations of ionization potential and micropolarity in the mixed micellar region have been investigated as a function of surfactant composition and the obtained results in mixed micellar medium has been compared to the normal micelles. The critical micelle concentration (CMC) values determined at various surfactant compositions are lower than the ideal values indicating a synergistic interaction. The interaction parameter (β) and micellar stability has been calculated using regular solution theory.