Excited-state proton transfer from pyranine to acetate in methanol

Excited-state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulphonate, HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectroscopy. The rate constant of direct proton transfer from pyranine to acetate (k1) is calculated to be ~1 × 10^ 9 M^ –1 s^ –1 . This is slower by about two orders of magnitude than that in bulk water (8 × 10 ^10 M ^–1 s ^–1 ) at 4 M acetate.