Effects of calcium chloride on the proton transfer dynamics of 4-hydroxy-1-naphthalenesulphonate in alcohol/water mixtures

Proton transfer from the excited 4-hydroxy-1-naphthalenesulphonate to the water solvent is studied in n-alcohol/water (70:30) mixtures in the presence of calcium chloride. The proton acceptor concentration is found to increase initially with an increase in the concentration of calcium chloride reaching a maximum followed by a decrease in the rate upon the addition of more calcium chloride. The non-linear dependence of the proton acceptor concentration against the concentration of calcium chloride is explained in terms of the structure breaking of hydrogen bonds, increasing the proton transfer rate initially, and the depletion of free water molecules due to hydration leading to a slowing down of the proton transfer rate.