Dynamics of solubilization of naphthalene and pyrene into dodecylammonium trifluoroacetate micelles

Abstract

A photochemical probe was used to determine the rate constant for a solubilizate molecule to escape from its parent micelle, where the quencher molecules for the excited probe are located exclusively outside of the micelle. Stern–Volmer kinetics of the solubilizates, naphthalene and pyrene, in dodecylammonium trifluoroacetate micelles were analyzed at 35°C in order to determine their exit (k_-) and entry rate constants (k₊) from and to the micelle. The ion Ag⁺, with the same charge as the micelle, was used as the quencher for the excited probes. The values of k_- (k₊) were determined to be 6.11×10⁶ s^-1 (2.25×10¹² d mol^-1 s^-1) and 1.39×10⁶ s^-1 (1.51×10¹³ d mol^-1 s^-1) for naphthalene and pyrene, respectively, from analysis of the Stern–Volmer quenching ratio vs. the quencher concentration in micellar solutions. Analysis using the initial slope of the curve led to slightly lower values for the rate constants. The spontaneous decay rate constants for the excited probes in the aqueous bulk and solubilized in the micelles and the quenching rates of excited probes by the quencher were also determined from this analysis. The same experiments were also conducted with anthracene, but the final kinetic results were not discussed as they could not be readily explained.