Diffusion Coefficients Estimated by Dynamic Fluorescence Quenching at High Pressure: Pyrene, 9,10-Dimethylanthracene, and Oxygen in n-Hexane

The fluorescence quenching of pyrene (PY) by carbon tetrabromide (CBr4) at pressures of up to 400 MPa in n-hexane was investigated. It was found that the fluorescence quenching is not fully, but nearly, diffusion-controlled. From the pressure-induced solvent viscosity dependence, the quenching rate constant, kq , was separated into the contributions of the bimolecular rate constant in the solvent cage, kbim, and that for diffusion, kdiff . Using the values of kdiff separated, together with those of the diffusion coefficient of CBr4 , the diffusion coefficients of PY were successfully estimated. This analysis was applied to the quenching systems of 9,10-dimethylanthracene (DMEA)/CBr4 and of PY/O2 and DMEA/O2 that were studied previously. Using the values of kdiff for these systems, together with those of the corresponding diffusion coefficients of the fluorophore or quencher, the diffusion coefficients of DMEA and O2 were also evaluated. Based on the results, the pressure-induced solvent viscosity, g, dependence on the diffusion coefficients is discussed