The behavior of acridine orange base (AOB) in nonaqueous reverse micelles composed of n-heptane/AOT/polar solvent has been performed. Ethylene glycol (EG), propylene glycol (PG), glycerol (GY), formamide (FA), dimethylformamide (DMF), and dimethylacetamide (DMA) were employed as water Substitutes. The Studies were performed by static and time-resolved emission spectroscopy. Thus, the distribution of AOB between the two pseudophases of the agggregates was quantified by measuring the partition constants from emission spectra at different surfactant concentration. Similar values to those obtained by means of absorption spectroscopy were obtained. This match is indicating that AOB is not experiencing partition during the lifetime of the excited state. Partitioning to the micelles is strongly favored in micelles containing hydrogenbond donor (HBD) solvents rather that) non-HBD solvents. Variations of fluorescence lifetimes with AOT concentration confirm these results. By the solvatochromic behavior of AOB in the different systems it is shown that the microenvironment at the interface is distinct from that of the bulk polar solvent, indicating that the probe senses no "free" solvent. The steady state anisotropy (< r >) was measured for EG/AOT/n-heptane and DMF/AOT/n-heptane systems as representatives for HBD and non-HBD polar solvents, respectively. The value of < r > is higher in the micelles containing EG than that obtained with DMF, and increases with AOT concentration. This is explained as due to highly structured polar solvents in the inner core. EG is interacting with the polar heads of AOT through hydrogen-bond interaction, while DNIF can only interact with the Na+ counterions. This is confirmed by the time-resolved emission spectra (TRES) of the probe in the micellar systems, in comparison with the bulk solvents. (c) 2005 Elsevier Inc. All rights reserved.