Excited state proton transfer from pyranine to acetate in a CTAB micelle

Proton transfer process of pyranine (8-hydroxypyrene-1,3,6-trisulfonate, HPTS) at the surface of a cationic micelle (cetyl trimethyl ammonium bromide, CTAB) has been studied by emission spectroscopy. At the CTAB micellar surface, pH is ~9.5 and the ground state pKa of HPTS is 10.2. These are higher compared to bulk water (pKa = 7.4 and pH 7). At the surface of the micelle, emission of HPTS is quenched by acetate ion with a bimolecular quenching constant, 3.5 × 107 M-1 s-1. This is markedly slower than the excited state proton transfer in a solvent separated HPTS-water-acetate complex in bulk water