Transient effects in the fluorescence quenching of a strong photoacid

Abstarct: Fluorescence quenching of 1-hydroxynaphthalene-4-sulfonate by water has been studied in methanol–water and ethanol–water mixtures. The fluorescence quenching has shown a significant deviation from the Stern–Volmer linearity at higher concentrations of water due to dynamic quenching along with transient effects and instantaneous quenching. Time-resolved fluorescence decay of the conjugate base of 1-hydroxynaphthalene-4-sulfonate in methanol–water mixture indicates the need of only one water molecule to hydrate the conjugate base aftermath of the dissociation of the photoacid. -- Highlights: • A strong photoacid shows positive deviation from Stern–Volmer plot. • It is explained in terms of transient effects and instantaneous quenching. • The deviation depends on the fluorescence lifetime and quencher concentration. • The Stern–Volmer and quenching constants have been obtained experimentally. • Only one water molecule is needed to hydrate the naphthalate ion