Nile Blue in Triton-X 100/benzene-hexane reverse micelles: a fluorescence spectroscopic study

We report the observation of ground state prototropic equilibrium of the dye Nile Blue in Triton-X 100/benzene-hexane reverse micellar system. In the absence of water, the deprotonated form of the dye is predominant. Addition of water produces the protonated form. At highest water loading, the equilibrium is still shifted towards the deprotonated form as revealed by the absorption spectrum. In neat Triton-X 100 also, the dye is present almost predominantly in the deprotonated form as revealed by the absorption spectrum. The average fluorescence lifetime of the dye is greater in neat Triton-X 100 than in Triton-X 100 reverse micelles, when no water is added. Addition of water to the reverse micelles increases the average lifetime of the deprotonated species. We offer possible explanations to the above observations by discussing the structure and properties of the Triton-X 100/benzene-hexane reverse micelles.