Excited-state proton transfer to methanol-water mixtures

Noam Agmon*, Dan Huppert, Asnat Masad, Ehud Pines

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We have measured the fluorescence decay of 8-hydroxypyrene-1,3,6-trisulfonate due to proton transfer to solvent in water-methanol mixtures. The data agree quantitatively with the reversible, diffusion-influenced proton-transfer mechanism in all solutions. No significant deviations from a short-time exponential decay or a long-time power law decay were found that could support a recently suggested water molecule diffusion mechanism. Solvent-induced variations in the deprotonation rate coefficient are very close to those in the corresponding equilibrium coefficient. Analysis of measured and literature pK data indicates that the composition dependence is mainly due to localized counterion stability in water-rich solutions and to proton stability in methanol-rich solutions. Quantitative agreement with literature compilations of proton-transfer free energy is obtained. These observations challenge the prevailing idea that a minimal cluster of four water molecules is the required proton acceptor in these solutions.

Original languageEnglish
Pages (from-to)10407-10413
Number of pages7
JournalJournal of Physical Chemistry
Issue number25
StatePublished - 1991


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