Issue 20, 2022

Ultrafast proton transfer of the aqueous phenol radical cation

Abstract

Proton transfer (PT) reactions are fundamental to numerous chemical and biological processes. While sub-picosecond PT involving electronically excited states has been extensively studied, little is known about ultrafast PT triggered by photoionization. Here, we employ femtosecond optical pump-probe spectroscopy and quantum dynamics calculations to investigate the ultrafast proton transfer dynamics of the aqueous phenol radical cation (PhOH˙+). Analysis of the vibrational wave packet dynamics reveals unusually short dephasing times of 0.18 ± 0.02 ps and 0.16 ± 0.02 ps for the PhOH˙+ O–H wag and bend frequencies, respectively, suggestive of ultrafast PT occurring on the ∼0.1 ps timescale. The reduced potential energy surface obtained from ab initio calculations shows that PT is barrierless when it is coupled to the intermolecular hindered translation between PhOH˙+ and the proton-acceptor water molecule. Quantum dynamics calculations yield a lifetime of 193 fs for PhOH˙+, in good agreement with the experimental results and consistent with the PT reaction being mediated by the intermolecular O⋯O stretch. These results suggest that photoionization can be harnessed to produce photoacids that undergo ultrafast PT. In addition, they also show that PT can serve as an ultrafast deactivation channel for limiting the oxidative damage potential of radical cations.

Graphical abstract: Ultrafast proton transfer of the aqueous phenol radical cation

Supplementary files

Article information

Article type
Paper
Submitted
31 jan 2022
Accepted
09 mai 2022
First published
10 mai 2022
This article is Open Access
Creative Commons BY-NC license

Phys. Chem. Chem. Phys., 2022,24, 12236-12248

Ultrafast proton transfer of the aqueous phenol radical cation

M. S. Bin Mohd Yusof, H. Song, T. Debnath, B. Lowe, M. Yang and Z. Loh, Phys. Chem. Chem. Phys., 2022, 24, 12236 DOI: 10.1039/D2CP00505K

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