Pyrene fluorescence at air/sodium dodecyl sulfate solution interface

The dependence of pyrene fluorescence spectra on the concentration of sodium dodecyl sulfate (SDS) was observed, where the solution was prepared from water saturated with pyrene. The values of the I-1/I-3 ratio from the bulk solution and from the upper meniscus region in an optical cell were similar but decreased rapidly around the critical micelle concentration (cmc) of SDS, indicating that pyrene molecules preferred to be solubilized in the micelles having a lower dielectric constant. The fluorescence intensity of the excimer indicated the concentration of pyrene molecules at the air/solution interface or the surface activity of pyrene molecules. In addition, the intensity from the meniscus region is much larger than that from the bulk at the concentrations below the cmc, whereas there was no difference in the intensity between the bulk and the meniscus above 8 mmol dm(-3) of SDS. The analysis of the fluorescence intensity from the excimer strongly suggests the presence of molecular aggregates that are favorable to the pyrene molecules just like the micelles in the bulk, making them less movable.