Effect of electrolytes on the excited-state proton transfer and geminate recombination

Pavel Leiderman, Rinat Gepshtein, Anna Uritski, Liat Genosar, Dan Huppert*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Time-resolved emission and steady-state fluorescence techniques are used to study the excited-state intermolecular proton transfer from 8-hydroxypyrene-1,3,6-trisulfonate (HPTS or pyranine) to water in the presence of inert salts, NaCl and MgCl2. At low salt concentrations, up to about 0.5 M MgCl2 or about 0.8 M NaCl, the time-resolved emission of both the photoacid and conjugate base can be quantitatively fitted by our diffusion-assisted geminate recombination model. In this concentration range, the proton transfer and geminate recombination rate constants are almost independent of the salt concentrations whereas the proton diffusion constant decreases as the salt concentration increases. At higher salt concentrations, the proton-transfer rate constant decreases while the recombination rate constant increases slightly. For the saturated solution of MgCl2 (about 5 M at room temperature), the steady-state emission consists of only a single band of the protonated photoacid. Careful examination of the time-resolved emission of HPTS in the presence of a large concentration of MgCl2 shows that the quality of the fit to the geminate recombination model is rather poor and we fail to find adjustable parameters for a good quality fitting. For this large concentration range of MgCl2 we were able to get a good fit of the experimental data with a model based on a distribution of proton-transfer rates. The model is consistent with an inhomogeneous water environment next to the excited HPTS molecule in such concentrated solutions.

Original languageEnglish
Pages (from-to)5573-5584
Number of pages12
JournalJournal of Physical Chemistry A
Issue number17
StatePublished - 4 May 2006


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