title: Effect of electrolytes on the excited-state proton transfer and geminate recombination.
abstract: 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 MgCl(2). At low salt concentrations, up to about 0.5 M MgCl(2) 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 MgCl(2) (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 MgCl(2) 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 MgCl(2) 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.
authors.affiliation: Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Israel.
authors.forename: Pavel
authors.initials: P
authors.lastname: Leiderman
authors.forename: Rinat
authors.initials: R
authors.lastname: Gepshtein
authors.forename: Anna
authors.initials: A
authors.lastname: Uritski
authors.forename: Liat
authors.initials: L
authors.lastname: Genosar
authors.forename: Dan
authors.initials: D
authors.lastname: Huppert
mesh_terms: D001190:Arylsulfonates / Q000737:chemistry*; D004573:Electrolytes / Q000737:chemistry*; D015636:Magnesium Chloride / Q000737:chemistry*; D011522:Protons; D012680:Sensitivity and Specificity; D012965:Sodium Chloride / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D001190:Arylsulfonates; D004573:Electrolytes; D011522:Protons; D015636:Magnesium Chloride; D014867:Water; D012965:Sodium Chloride; C005047:pyranine