Influence of Polarity and Viscosity of the Micellar Interface on the Fluorescence Quenching of Pyrenic Compounds by Indole Derivatives in AOT Reverse Micelles Solutions

The fluorescence quenching of the pyrene derivatives (4-(1-pyrenyl)butyl) trimethylammonium bromide (PBTMA), (1-(1-pyrenyl)methyl) trimethylammonium iodide (PMTMA), and 1-pyrene sulfonic acid (PSA) by indole methyl substituted in positions 1 and 2, tryptophan and tryptamine, was studied in AOT/heptane reverse micelles as a function ofR= [water]/[AOT]. In these systems the pyrenic probes are associated to the micellar interface. Bulk and intramicellar quenching rate constants were determined for neutral indoles. The quenching rate constants of PBTMA by indole or 1,2-dimethylindole increase withR,whereas for those for PMTMA or PSA by indole the increment is much smaller. For the quenchers, tryptophan and tryptamine, that are bound to the interface of the reverse micelle, the bimolecular intramicellar quenching rate constant is much lower than in water. The results can be explained by a high microviscosity of the interface, and a micropolarity similar to that sensed by other probes. Moreover, the observed trend in the rate constants whenRis varied is in line with the reported changes in micropolarity and microviscosity. Laser flash photolysis experiments show that in these systems the main result of the quenching process is the formation of the excited triplet of the probe.