Association of Nitrophenols to Sodium Dodecylsulfate Micelles

Abstract

The luminescence quenching of tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)32+) by 2-, 3-, and 4-nitrophenol (NO2PhOH), in their protonated forms, has been studied by static and time-resolved techniques in water and sodium dodecyl sulfate (SDS) aqueous solution. In water, the bimolecular rate constants were obtained separately from both techniques and they were coincident. The values were close to the diffusional limit. In the presence of SDS micelles at a fixed detergent concentration, the Stern–Volmer plots of τ0/τ vs quencher total concentration ([Q]t) were linear in the whole range of [Q]tused. However, the Stern–Volmer plots of the ratioI0/Ivs [Q]tin SDS micelles showed an upward deviating curve. From these plots ofI0/I, the concentrations of the NO2PhOHs in the micellar pseudophase were measured. The treatment of the data of both types of measurements let us determine the association constants (K) of the NO2PhOHs to SDS micelles and the exit (k−) and entrance (k+) rate constants of NO2PhOHs to the micelles. TheKvalues obtained from either static or time-resolved luminescence techniques were in agreement within experimental error. An electron-transfer mechanism was also proposed for the quenching reaction of the excited state Ru(bpy)32+by nitrophenols in which the metallic complex is oxidized.