Fluorescence Characteristics of 8-Quinolinethiol

Abstract

8-Quinolinethiol exhibits intense fluorescence in concentrated acids at an ordinary temperature, but this fluorescence is quenched by addition of water. In order to clear this mechanism, its excited singlet state properties in concentrated sulfuric or perchloric acid have been studied. Absorption and fluorescence spectra, prototropic equilibrium constants between cation and zwitterion, fluorescence quantum yields, fluorescence lifetimes and fluorescence polarization spectra were investigated.
With decreasing concentra tion of acids, the maxima in absorption and fluorescence spectra of 8-quinolinethiol were shifted to longer wavelength, and the quantum yield and the lifetime of the fluorescence were diminished. From the results obtained, the fluorescence of 8quinolinethiol in concentrated acid has been attributed to an exhibition of π-π^* transition due to protonation of quinoline nitrogen and to an inhibition of n-π^* transition.