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Issue 37, 2012
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Excited-state proton transfer and ion pair formation in a Cinchona organocatalyst

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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.

Graphical abstract: Excited-state proton transfer and ion pair formation in a Cinchona organocatalyst

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Publication details

The article was received on 09 May 2012, accepted on 30 Jul 2012 and first published on 30 Jul 2012


Article type: Paper
DOI: 10.1039/C2CP41483J
Citation: Phys. Chem. Chem. Phys., 2012,14, 13019-13026
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    Excited-state proton transfer and ion pair formation in a Cinchona organocatalyst

    T. Kumpulainen and A. M. Brouwer, Phys. Chem. Chem. Phys., 2012, 14, 13019
    DOI: 10.1039/C2CP41483J

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