Luminescence behaviour of phenosafranin in reverse micelles of AOT in n-heptane

The absorption and fluorescence properties of the cationic dye phenosafranin (PSF) solubilised in the reverse micelles of the surfactant aerosol OT (AOT) in n-heptane were studied as a function of water content, w(0) = ([H2O]/[AOT]). The room temperature emission of PSF in reverse micelles at w(0) = 0 show a significantly blue shifted maximum as compared with that in pure water. A plot of fluorescence polarisation anisotropy (r) against increasing w(0) shows an increase in the rigidity of the dye environment up to w(0) approximate to 10, where it maximises and then falls off to attain a steady value between w(0) = 25-30. Even at this high w(0) the anisotropy of the embedded dye molecule is appreciably higher than that of the dye in bulk water. Lifetime measurements at different w(0) values showed single exponential decay character. Relevant absorption and luminescence data in representative homogeneous solvents and in low temperature (77 K) glass are also reported. The observations have been interpreted in terms of the location of the dye molecule and changes in its environment with changes in w(0), in the AOT reverse micelles. (C) 1997 Elsevier Science S.A.