Salt effects on steady-state quantum yields of ultrafast, diffusion-influenced, reversible photoacid dissociation reactions

Ehud Pines, Dan Huppert, Noam Agmon

Research output: Contribution to journalArticlepeer-review

48 Scopus citations

Abstract

The steady-state fluorescence quantum yields of the protonated and deprotonated forms of 8-hydroxypyrene-1,3,6-trisulfonate are determined in three solvents as a function of NaNO3 concentration. The measured quantum yields, and therefore also the overall dissociation rate coefficients, decrease with increasing salt concentration, in contrast to Brönsted's classical model for primary salt effects. This is a consequence of the reversibility and the nearly diffusion-controlled recombination rate of the proton in the reaction studied. A quantitative analysis is based on newly derived results for reversible diffusion-influenced reactions. Comparison with experiment is made for two screened potentials. Numerical integration with the Debye-Hückel potential indicates that it overestimates the salt effect. A second model (the "naive approximation") is based on a simple screened potential from which analytical expressions for reaction yields and rates are derived. It shows better agreement with experiment in the range 20-200 mM salt.

Original languageEnglish
Pages (from-to)666-674
Number of pages9
JournalJournal of Physical Chemistry
Volume95
Issue number2
DOIs
StatePublished - 1 Jan 1991
Externally publishedYes

ASJC Scopus subject areas

  • General Engineering
  • Physical and Theoretical Chemistry

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