Issue 30, 2020

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

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 of 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.

Graphical abstract: Broadband fluorescence reveals mechanistic differences in excited-state proton transfer to protic and aprotic solvents

Supplementary files

Article information

Article type
Edge Article
Submitted
15 Jun 2020
Accepted
07 Jul 2020
First published
08 Jul 2020
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2020,11, 7963-7971

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

P. Verma, A. Rosspeintner, B. Dereka, E. Vauthey and T. Kumpulainen, Chem. Sci., 2020, 11, 7963 DOI: 10.1039/D0SC03316B

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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