Solvent effects on intramolecular proton transfer

The proton transfer times for a 2-phenyl-benzotriazole (HOPB) having an octyl group on the 5-position are essentially the same as those found earlier with 5-methyl substituent but the overall rotational reorientation time is significantly increased with the octyl substituent. A systematic study of the proton transfer in 1-alkanols has revealed that the rates for both methyl and octyl derivatives are close to the solvent longitudinal relaxation times, τ_L. Significant solvation of excited molecules is not occurring during the proton transfer lifetime. It is concluded that the proton transfer is a tunneling process that is slowed down by the multidimensionality of the potential surface and by the solvent fluctuations.