Volume 275, February 2026, 113116Author links open overlay panel, , , , , , , Highlights•

pKa of chromophoric photoacid PPd(C6F5)3OH drastically drops from 6.49 to 0.97 upon photoexcitation.

•

Ultrafast proton transfer (342 fs lifetime) characterized in solution.

•

Distinct visible-to-near infrared spectra for neutral, deprotonated, and excited states.

Abstract

Coordinated electron and proton movement drive bioenergetic functions. Relative to electron transfer reactions, tracking proton transport over fast-to-ultrafast time scales is challenging. Optical resolution of proton transfer dynamics can take advantage of chromophoric photoacids that not only trigger proton migration upon photoexcitation, but produce distinct spectroscopic changes associated with protonation/deprotonation. In this work, we report the design of a hydroxy-substituted electron deficient Pd porphyrin, PPd(C6F5)3OH; upon photoexcitation, the acidity constant of this weak acid (pKa = 6.49) dramatically drops (pKa* = 0.97). Electronic excitation of PPd(C6F5)3OH triggers an ultrafast proton transfer reaction (PPd(C6F5)3OH +:B + hυ → 1[PPd(C6F5)3OH]* +:B → 1[PPd(C6F5)3O]−* + HB+; τPT = 342 fs) to a H-bonded base (B) in solution. Both PPd(C6F5)3OH and its conjugate anion PPd(C6F5)3O− exhibit distinct vis-NIR spectral features for their respective ground and excited states. Because the electroni-cally excited triplet lifetimes of these species exceed tens of microseconds, the PPd(C6F5)3OH photoacid defines an ideal cofactor to probe light-triggered proton release and track long-range proton migration in protein environments.

Graphical abstractDownload: Download high-res image (138KB)Download: Download full-size imageSection snippetsCRediT authorship contribution statement

Jiaqi Zhu: Writing – review & editing, Writing – original draft, Investigation, Formal analysis. Rui Liu: Writing – review & editing, Methodology, Investigation, Data curation, Conceptualization. Jarrett P. Mansergh: Writing – review & editing, Methodology. Minting Ouyang: Writing – review & editing, Methodology. Lindsay R. Pederson: Writing – review & editing, Methodology. Ian Bakanas: Writing – review & editing, Methodology. William F. DeGrado: Writing – review & editing, Resources, Project

Declaration of competing interest

The authors declare no competing interests.

Acknowledgements

This work was funded by National Science Foundation through CHE-2528383, CHE-2528384, and ITE-2448848. MJT is indebted to the United States Department of Energy (DE-SC0001517) and the United States Air Force Office of Scientific Research (FA9550-20-1-0121) for research infrastructure enabling these transient dynamical spectroscopic experiments, and WFD acknowledges the National Institutes of Health (R35GM122603) for support. J.Z. gratefully acknowledges Duke University for C. R. Hauser Memorial

References (31)Y. Sasano et al.Ion-pairing π-electronic systems: ordered arrangement and noncovalent interactions of negatively charged porphyrins

Chem. Sci.

(2021)

A. Migliore et al.Biochemistry and theory of proton-coupled electron transfer

Chem. Rev.

(2014)

K. Takematsu et al.Hole hopping across a protein–protein interface

J. Phys. Chem. B

(2019)

J.J. Goings et al.Nonequilibrium dynamics of proton-coupled electron transfer in proton wires: concerted but asynchronous mechanisms

ACS Cent. Sci.

(2020)

R. Tyburski et al.Proton-coupled electron transfer guidelines, fair and square

J. Am. Chem. Soc.

(2021)

H.B. Gray et al.Long-range electron transfer

Proc. Natl. Acad. Sci. USA

(2005)

D.N. Beratan et al.Charge transfer in dynamical biosystems, or the treachery of (static) images

Acc. Chem. Res.

(2015)

N.M. Ennist et al.De novo protein design of photochemical reaction centers

Nat. Commun.

(2022)

D.M. Needham et al.A distinct lineage of giant viruses brings a rhodopsin photosystem to unicellular marine predators

Proc. Natl. Acad. Sci. USA

(2019)

P. Greife et al.The electron–proton bottleneck of photosynthetic oxygen evolution

Nature

(2023)

L.M. Tolbert et al.Photoexcited proton transfer from enhanced photoacids

J. Am. Chem. Soc.

(1994)

L.M. Tolbert et al.Excited-state proton transfer: from constrained systems to “super” photoacids to superfast proton transfer

Acc. Chem. Res.

(2002)

M. Prémont-Schwarz et al.Ultrafast excited-state proton-transfer reaction of 1-naphthol-3,6-disulfonate and several 5-substituted 1-naphthol derivatives

J. Phys. Chem. B

(2013)

T. Kumpulainen et al.Ultrafast elementary photochemical processes of organic molecules in liquid solution

Chem. Rev.

(2017)

S.G. DiMagno et al.Facile synthesis of meso-tetrakis(perfluoroalkyl)porphyrins: spectroscopic properties and x-ray crystal structure of highly electron-deficient 5,10,15,20-tetrakis(heptafluoropropyl)porphyrin

J. Org. Chem.

(1994)

View full text

© 2025 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.