Intramolecular proton transfer as a preliminary step for proton dissociation in 2-naphthol-3,6-disulfonate

Time-resolved and steady-state fluorescence techniques were employed to study the intramolecular and intermolecular proton-transfer processes occurring in the first excited electronic state of 2-naphthol-3,6-disulfonate. It was found that the first step after excitation by a short light pulse is an intramolecular proton transfer from the hydroxy group to the adjacent sulfonate group. Subsequently, at a slower rate, the proton is transferred to the solvent. The intramolecular proton transfer is mediated by water molecules. The solvated proton has a finite probability to recombine geminately with the parent molecule via either of the proton-accepting moieties, the hydroxy group or the sulfonate groups. We used the exact transient numerical solution of the Debye-Smoluchowski equation to quantitatively describe the proton geminate recombination reaction.