The interaction of the fluorescent probe 3-phenylureidoquinoline with surfactant assemblies has been investigated using fluorescence spectroscopic and computational techniques. The non-radiative deactivation rates are found to be suppressed in micelles. In the negatively charged SDS micelle, the cation is found to form, leading to a marked shift in fluorescence. This is explained by a consideration of the local pH and altered pK(a) of the fluorophore. In reverse micelle the gradual addition of water remarkably enhances the rate of non-radiative depopulation. (c) 2006 Elsevier B.V. All rights reserved.