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Scientific article
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Broadband fluorescence reveals mechanistic differences in excited-state proton transfer to protic and aprotic solvents

Published inChemical Science, vol. 11, no. 30, p. 7963-7971
Publication date2020
Abstract

Excited-state proton transfer (ESPT) to solvent is often explained according to the two-step Eigen-Weller model including a contact ion pair (CIP*) as an intermediate, but general applicability of the model has not been thoroughly examined. Furthermore, examples on the spectral identification of CIP* are scarce. Here, we report on a detailed investigation of ESPT to protic (H2O, D2O, MeOH and EtOH) and aprotic (DMSO) solvents utilizing a broadband fluorescence technique with sub-200 fs time resolution. The time-resolved spectra are decomposed into contributions from the protonated and deprotonated species and a clear signature of CIP* is identified in DMSO and MeOH. Interestingly, the CIP* intermediate is not observable in aqueous environment although the dynamics in all solvents are multi-exponential. Global analysis based on the Eigen-Weller model is satisfactory in all solvents, but the marked mechanistic differences between aqueous and organic solvents cast doubt on the physical validity of the rate constants obtained.

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Citation (ISO format)
VERMA, Pragya et al. Broadband fluorescence reveals mechanistic differences in excited-state proton transfer to protic and aprotic solvents. In: Chemical Science, 2020, vol. 11, n° 30, p. 7963–7971. doi: 10.1039/D0SC03316B
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ISSN of the journal2041-6520
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Creation08/13/2020 9:16:00 AM
First validation08/13/2020 9:16:00 AM
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