Rostock 2019 – scientific programme
Parts | Days | Selection | Search | Updates | Downloads | Help
MO: Fachverband Molekülphysik
MO 11: Photochemistry
MO 11.4: Talk
Wednesday, March 13, 2019, 11:30–11:45, S HS 001 Biologie
Tuning Excited-State Proton Transfer of a Super-Photoacid — •Niklas Suelzner1, Bastian Geissler1, Alexander Grandjean2, Gregor Jung2, and Patrick Nuernberger1 — 1Physikalische Chemie II, Ruhr-Universität Bochum, 44780 Bochum — 2Biophysikalische Chemie, Universität des Saarlandes, 66123 Saarbrücken
Special molecules, referred to as photoacids, exhibit an acidity increase upon irradiation. Triggered by photoexcitation, such molecules perform an excited-state proton transfer (ESPT) if suitable proton acceptors are present. Moreover, super-photoacids, i.e. with a negative pKa value in the excited-state, are even strong enough for ESPT in non-aqueous solution. In previous studies, we observed ESPT from the neutral, super-photoacidic HPTS-derivative hydroxypyrene-tris(hexafluoropropanylsulfonate) to acetone. However, the influence of water on ESPT in this aprotic environment remained unresolved.
The present study investigates the ESPT kinetics of this photoacid in binary acetone-water mixtures by time-resolved fluorescence spectroscopy on the picosecond timescale. Owing to the fluorescence of both the protonated and deprotonated species, information on ESPT is hereby directly accessible through the fluorescence dynamics. First, we reveal the severe effect of water in the mixtures constituting in an acceleration of ESPT with increasing concentration. Afterward, we demonstrate that the water-driven acceleration can be antagonized by adding an excess of strong acid. Based on this, we infer that strong acids can be used to effectively deactivate water towards ESPT.