Intramolecular Proton Transfer in the Excited Singlet State of 3-Hydroxy-2-naphthoic Acid

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Abstract
Studies of fluorescence quenching via intramolecular proton transfer are described for the systems 3‐hydroxy‐2‐naphthoic acid in several solvents. It has been found that bases which promote the proton transfer in nonpolar solvents function by parallel static and dynamic mechanisms and that the mechanism proposed by Hirota, which assumes rapid establishment of the proton transfer equilibrium during the lifetime of the excited state, is inadequate. The mechanisms of both the static and the dynamic processes have been investigated by using fluorescence lifetime techniques and by making steady‐state fluorescence quenching measurements. The results for various solvents and various temperatures are reported for the acid, its methyl ester, and the corresponding methoxy derivative.