Reaction volume and rate constants for the excited-state proton transfer in aqueous solutions of naphthols

In this Letter we report the time-resolved determination of the volume changes for the excited-state deprotonation of 1-naphthol, 2-naphthol and 1-naphthol-3,6-disulphonate and the neutralization of the ground-state naphtholate anions with the protons free in solution. Photoexcitation of the naphthols leads to a fast contraction of the solution due to the solvation of the newly formed ions and is followed by an expansion of equal extent, due to the back recombination reaction. The apparent rate constant of the recombination reaction depends on the concentration of protons free in solution in accordance with a pseudo-first-order reaction model.