Fluorescent probes for structural and distance effect studies in micelles, reversed micelles and microemulsions

The present review is an attempt to highlight the use of fluorescent probes to study the structural parameters and distance effect in micelles, reversed micelles and microemulsions. Fluorescence quenching has also been used as a powerful tool to obtain information on the compositional, structural and dynamic characteristics of these organized assemblies. The work relating to the use of fluorescent probes has been reviewed mostly from the literature of the last two decades. The binding constant, critical micelle concentration, micellar aggregation number, and distribution of probes and quenchers have been evaluated for micelles by using various probes. Much attention is focused on the nature of the entrapped water within the core of the reversed micelle. The presence of four principal microenvironments: an inner 'free' water pool, a bound water region, the interface, and the surrounding hydrocarbon continuum are indicated in reversed micelles. Various studies in microemulsions have been carried out by using mostly pyrene as the fluorophore. The dielectric constant values, size and polydispersity, aggregation behaviour, photochemical transfer of an electron and a proton have been carried out by various workers using different probes. These organized assemblies have a structural advantage of compartmentalizing the fluorophore and quenchers in their various sites. In view of this situation studies on distance effect have been carried out by various workers using different probes and quenchers. The microemulsions separate the oil and water pools clearly by a surfactant membrane and hence distance effect is expected to be noticed very clearly in this system. In the last two decades of the review almost no work in reversed micelles and very few in microemulsions have come to our notice. (C) 1999 Elsevier Science B.V. AU rights reserved.