Unusual temperature dependence of excited state proton transfer rates in alcohols

The reversible proton dissociation and geminate recombination of photoacids is studied as a function of temperature in alcohols. For this purpose we used a strong photoacid 5,8-dicyano-2-naphthol (DCN2) (pK(a)* similar to -4.5 in water) that is capable to transfer a proton to alcohols. The experimental data are analyzed by the Debye-Smoluchowski equation solved numerically with boundary conditions to account for the reversibility of the reaction. We propose a qualitative model to describe the unusual temperature dependence of the proton-transfer rate constant in alcohols in the liquid phase.