highlight 5 2017

We are investigating the dynamics of an excited-state proton transfer from a photoacid (ROH) to DMSO using fs broadband fluorescence up–conversion (FLUPS). The microscopic reaction mechanism consists of a reversible short-range proton transfer to produce contact ion pairs (CIP) followed by a full dissociation into free ions (RO). All three species have distinct emission bands which exhibit solvent relaxation (dynamic Stokes shift) in parallel with population dynamics (bottom right). Global target analysis based on the scheme presented in top left enables disentangling all associated rate constants and gives access to the intrinsic population dynamics presented in top right. In addition, the dynamics of the solvent relaxation can be independently accessed through the emission peak positions of each band. The results indicate that the establishment of the equilibrium between the ROH and CIP forms is driven by the solvent relaxation, whereas the dissociation proceeds after the solvent relaxation as a normal over-the-barrier reaction.

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Eric Vauthey

Physical Chemistry Department - Sciences II - University of Geneva
30, Quai Ernest Ansermet - CH-1211 Geneva 4 (Switzerland)


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