Issue 24, 2025

pH-dependent ultrafast photodynamics of p-hydroxyphenacyl: deprotonation accelerates the photo-uncaging reaction

Abstract

Photolabile protecting groups (PPGs) possess broad application potential as they allow spatially and temporally controlled release of the protected group. While the photochemistry of many PPGs has been studied in detail, data under aqueous conditions or depending on the pH are extremely rare. However, for applications under biological conditions in water, knowledge about the photochemistry under these is critical. Here, we studied the pH-dependent reaction dynamics of para-hydroxyphenacyl (pHP), one prominent example of PPGs, by ultrafast transient absorption spectroscopy and quantum chemical simulation. At neutral pH, the para-hydroxyl group of pHP is protonated and photoproduct formation occurs within less than 1 ns from a triplet state. At basic pH, the main scaffold gets deprotonated leading to a bathochromic shift of the characteristic absorption. Upon deprotonation the substrate release occurs directly from a singlet state, shortcutting the rate determining step of intersystem crossing (ISC) in the neutral case, resulting in an acceleration of the photochemical reaction with photoproduct formation observed at ∼1 ps.

Graphical abstract: pH-dependent ultrafast photodynamics of p-hydroxyphenacyl: deprotonation accelerates the photo-uncaging reaction

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Article information

Article type
Paper
Submitted
18 Mar 2025
Accepted
20 May 2025
First published
23 May 2025
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2025,27, 12899-12907

pH-dependent ultrafast photodynamics of p-hydroxyphenacyl: deprotonation accelerates the photo-uncaging reaction

Y. Pfeifer, T. Stensitzki, J. Dostál, E. Titov, M. Kloz, P. Saalfrank and H. M. Müller-Werkmeister, Phys. Chem. Chem. Phys., 2025, 27, 12899 DOI: 10.1039/D5CP01049G

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