Excited state reaction kinetics of 4-hydroxy-1-naphthalenesulphonate in various alcohol-water mixtures

Proton transfer reaction from the excited state of 4-hydroxy-1-naphthalenesulphonate has been investigated in methanol-water, ethanol-water, 1-propanol-water mixtures at different temperatures. A mode-locked Nd:YAG laser in combination with a cavity-dumped synchronously-pumped dye laser is used to excite the probe. Fluorescence decay and time-resolved spectra are recorded with picosecond photon counting spectrometer.;Based on time-resolved spectra, two possible mechanisms have been proposed to explain the proton transfer process to water in methanol- and ethanol-water mixtures and 1-propanol-water mixture.;The decay is single exponential in all solutions and proton transfer rate is found to increase with increasing temperature and water concentration. A cluster of two water molecules is found to be the proton acceptor. Two new models are proposed to explain the proton transfer process of the probe molecule in methanol- and ethanol-water mixtures and 1-propanol-water mixture. The addition of calcium chloride to the solvent mixtures is observed to decrease the dissociation rate of excited 4-hydroxy-1-naphthalenesulphonate. The faster dissociation rate of the excited probe in the presence of urea is due to the acceptance of the dissociated proton by urea.