Variations of fluorescence efficiencies of 9-(10H)-acridone and its 4-methoxy derivative with ph. excited-state proton transfer in very weak acids and

Abstract

Acridone and its 4-methoxy derivative behave as very weak acids in their lowest excited singlet states. This behavior is shown to account for the pH dependences of their fluorescence spectra in alkaline solutions. 4-Methoxyacridone is also a very weak base in its lowest excited singlet state, which results in a pH dependence of its fluorescence spectrum in dilute acidic media. Acridone, although functioning as a very weak base in its lowest excited singlet state, in acidic ethanolic water, does not demonstrate excited-state proton exchange in acidic “pure” water. This suggests selective solvation by ethanol in the mixed solvent.