Excited-State Reactions of Coumarins in Aqueous Solutions. IV. The Fluorescence Quenching of 7-Ethoxycoumarins by Inorganic Ions in Micellar Solutions of Sodium Dodecyl Sulfate

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Abstract
The effect of added salts (NaCl, NaBr, CsCl) on the fluorescence behavior of 7-ethoxycoumarin (7EC) and 7-ethoxy-4-methylcoumarin (7E4MC) has been studied in aqueous micellar solutions of sodium dodecyl sulfate (SDS). Data on the fluorescence quenching as a function of the salt concentration are analyzed in terms of a proposed two-reactive-state (aqueous and micellar phases) model. The results are in good accord with the model and permit the evaluation of the quenching-rate constants attributable to Br− and Cs+ respectively in the two phases. Quenching mechanisms influencing the fluorescence yield are discussed on the basis of the electrostatic force among micelles and quenchers, the electron-transfer reaction from anion to fluorescer, and the hydration degree of the quencher ions.

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