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Updated: May 19, 2026

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
Published on: July 19, 2019
Excited-state proton transfer and ion pair formation in a Cinchona organocatalyst
Tatu Kumpulainen1, Albert M Brouwer
1Van't Hoff Institute for Molecular Sciences, Faculty of Science, University of Amsterdam, PO Box 94157, 1090 GD Amsterdam, The Netherlands.
Abstract:
The excited-state proton transfer and subsequent intramolecular ion pair formation of a cupreidine-derived Cinchona organocatalyst (BnCPD) were studied in THF-water mixtures using picosecond time-resolved fluorescence together with global analysis. Full spectral and kinetic characterization of all the fluorescent species allowed us to monitor the 3-step process for the ion pair dissociation. In the first step, proton transfer occurs through a water "wire" from the 6-hydroxyquinoline unit (excited-state acid) to the covalently bonded basic quinuclidine moiety, resulting in a hydrogen bonded ion pair. This was confirmed by the observed kinetic isotope effect in the presence of heavy water. In the second step, the formed ions are further solvated by a few solvent molecules, producing the solvent separated ion pair. Finally, a fully solvated ion pair is formed. The 5-exponential global model derived from the reaction scheme describes the experimental data very well.
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