Hannover 2020 – scientific programme

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MO: Fachverband Molekülphysik

MO 10: Collisions and Reactions

MO 10.9: Talk

Wednesday, March 11, 2020, 13:00–13:15, f142

Switching between proton vacancy and excess proton transfer using a bifunctional photoacid with the help of a third reaction partner — •Marius-Andrei Codescu, Oleg Kornilov, and Erik T.J. Nibbering — Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, 12489 Berlin, DE

Proton exchange between an acid and a base in protic solvents may in general occur along two different pathways. Recent results obtained on the bifunctional photoacid 7-hydroxyquinoline (7HQ) in water-methanol mixtures has been concluded to take place via a methoxide/hydroxide transport mechanism between the proton-donating OH group and the proton-accepting quinoline group on a timescale of tens to hundreds of picoseconds [Ekimova et al., J. Am. Chem. Soc. 141, 14581 (2019)]. Here, we show that by using cesium formate (Cs+ HCOO-) as a third reaction partner, it is possible to steer the reaction dynamics in such a fashion that the excess proton transfer pathway takes over as a dominant reaction mechanism. We follow the reaction kinetics by probing IR-active marker modes of different charged states of 7HQ, and of formic acid, in methanol solution using femtosecond UV-pump IR-probe spectroscopy. A dedicated analysis of the transient IR spectra results in a consistent and quantitative picture of the reaction mechanism for the 7HQ-formate reaction pairs, where the formate acts as an essential component in facilitating a full excess proton transport pathway from the proton-donating OH group to the proton-accepting quinoline group of 7HQ, before the regular proton vacancy (methoxide) transfer pathway can come in full effect.