Quenching of excited state pyrene by halothane in poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) triblock copolymers

Time-resolved fluorescence quenching of excited state pyrene by halothane w as investigated in aqueous solutions of poly(oxyethylene)-poly(oxypropylene )-poly(oxyethylene) triblock copolymers, P84, P104, and F38, at 25 degrees C. The occupancy number of halothane in the block copolymer micelles and th e dispersive factor were obtained from nonlinear least-squares fitting of t he immobile quencher-probe and dispersive kinetic models, respectively. It is shown that these parameters depend on the concentration of halothane in the system and the hydrophobic/hydrophilic balance of the block copolymers. The application of dispersive kinetics appears to be a suitable technique to investigate the self-aggregation behavior of self-assembly systems. Expo nential series lifetime-distribution analysis was also carried out and the results support the presence of aggregates of triblock copolymers in these systems. The results of this study suggest that halothane molecules distrib ute primarily in the core of the micelles but, upon saturation of the core, begin to locate in the corona of the block copolymer aggregates.