MOLECULAR-TRANSPORT IN POROUS SILICA - QUENCHING OF FLUORESCENCE FROM SURFACE-IMMOBILIZED PYRENE

Quenching of fluorescence from a surface-immobilized probe is developed as a method for measuring molecular transport in porous silica. In these experiments, 3-(1-pyrenyl)propyldimethylchlorosilane is covalently bonded to the surface of porous silica, and the rates of fluorescence quenching of this fluor by iodine were measured in a series of primary alcohols. Interfacial quenching rates were compared to those measured for 1-methylpyrene in free solution in the same solvents. Differences in the measured rates of quenching at the liquid/solid interface could be attributed to the volume excluded from quencher by the solid surface. A simple hemispherical diffusion model provided reasonable predictions of the rates of quenching based on the diffusion coefficients of iodine measured in free solution. The results indicate that the viscosity of alcohols within the pores of silica does not differ significantly from bulk solution values.