The different pKa values of some hydroxyarenes between the ground state and the excited state have shown the importance of proton transfer kinetics. The dissociation of proton and the reorientation of solvent structure which generally is a water structure are two main steps involved in the proton transfer process [1-4]. Based on the time-resolved fluorescence decay, a Zundel (H5O2+) form of protonated water structures has been proposed for the strong photoacids such as 2-naphthol-5-sulfonate and 1-naphthol-4-sulfonate. The bi-exponential decay of excited 2-naphthol-5-sulfonate suggests the need of stable hydration to the photobase aftermath of proton transfer [5]. The difference of excited-state proton transfer mechanism  shown in the time-resolved emission study of 1-naphthol-4-sulfonate in methanol- water and n-propanol-water mixtures indicates the dominant role of the water structure in the proton transfer process [6]. The fluorescence decays of the photobases of 2-naphthol-5-sulfonate and 1-naphthol-4-sulfonate are found to be bi-exponential [7] and the fluorescence decay rate between 11 M and 42 M of water concentration has exhibited the need of one water molecule to hydrate the photobase. It has been observed that water-dependent fluorescence decay of the photobase is independent of the type of alcohol-water mixtures at least for methanol, ethanol, and n-propanol. The position of sulfonate substituent in the hydroxyarene also plays a role in the stability and hence the basicity of the photobase.  The need of the water dimer may be regarded as the need of each water molecule in the hydration of the proton and the photobase in the alcohol-water mixtures. [1] Kalish,N. B-M., Shandalov, E., Kharianov, V., Pines, D., Pines, D., J. Phys. Chem. A., 2011 , vol. 115, pp.4063-4075.[2] Agmon, N., Huppert, D., Massad, A., Pines, E., J. Phys. Chem., 1991 , vol. 95, pp.10407-10413.[3] Presiado, I., Erez, Y., Gepshtein, R., Huppert, D., J. Phys. Chem. C., 2009 , vol. 113, pp. 20066-20075.[4] Htun, M. T., Suwaiyan, A., Klein, U. K. A.,Chem. Phy. Lett., 1997 , vol. 264, pp. 285-291.[5] Htun, M. T., Chem. Phy. Lett., 2011 , vol. 510, pp. 73-77.[6] Htun, M. T., Suwaiyan, A., Klein, U. K. A.,Chem. Phy. Lett., 1995 , vol. 243, pp. 506-511.[7] Htun, M. T., Proceedings of 2nd Annual International Conference on Chemistry, Chemical Engineering, and Chemical Process(CCECP 2014), Singapore, 2014 , pp. 41-46.

Time-resolved fluorescence study of excited-state proton transfer

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.