Erlangen 2018 – wissenschaftliches Programm
MO 13.7: Poster
Dienstag, 6. März 2018, 16:15–18:15, Orangerie
The Effect of Water on the Dynamics of a Superphotoacid in Acetone–Water Mixtures — •Niklas Suelzner1, Bastian Geissler1, Johannes Knorr1, Christian Spies1, Björn Finkler2, Gregor Jung2, and Patrick Nuernberger1 — 1Physikalische Chemie II, Ruhr-Universität Bochum, 44780 Bochum — 2Biophysikalische Chemie, Universität des Saarlandes, 66123 Saarbrücken
Photoacids exhibit a higher tendency to transfer an acidic proton in their electronically excited state compared to the ground state, which can trigger an excited-state proton transfer (ESPT). Using time-resolved spectroscopy, the ESPT process can be investigated on its actual timescale. Previous studies disclosed that the particularly strong photoacid hydroxypyrene-tris(hexafluoropropanylsulfonate) is capable of performing an ESPT even in the weakly basic solvent acetone. The role of water acting as an impurity in such aprotic, polar solvents remained unsettled though and might have a severe effect.
In this study, the influence of water on the ESPT of this photoacid in acetone–water mixtures was scrutinized by use of time-resolved streak camera fluorescence spectroscopy. Acetoneous samples with linearly increasing amounts of water (0 – 5 %) revealed a significant enhancement of the ESPT rate by nearly one order of magnitude. A further study on the alternating effect of adding water and acidifying the solution demonstrated that the observed ESPT acceleration was partially reversible. We infer that the water molecules act as acceptors facilitating the proton transfer but can be passivated by acidification.