DIFFUSION OF EXCITED BIANTHRYL IN MICROHETEROGENEOUS MEDIA

We studied the time-resolved bathochromic shifting of the fluorescence of bianthryl (BA) in micelles and bilayered membranes. Whatever the medium, the kinetics are complex but an isoemissive point is observed on the time-resolved fluorescence spectra. The polarized fluorescence and the kinetics of the decay show that, in bilayers (phosphatidylcholines and distearyldimethylammonium chloride), excitation energy transfer and trapping takes place. In micelles, physical diffusion of BA occurs from the core of the micelle to the water interface. We show that the diffusion is controlled by the existence of energy barriers and wells inside the micelles. This potential surface is defined by the variation of the chemical affinity of the probe through the micelle. The kinetics of the decay establishes that, in cetyltrimethylammonium chloride (CTAC) micelles, BA is localized among polar head groups in a well 1-2 angstrom wide. In sodium dodecyl sulfate, the inner population diffuses at a constant rate of 10(8) s-1. This reveals the existence of a skin, not observed in CTAC, that isolates BA molecules from the water.