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PreprintCC BYChemRxiv

Substituent Effects on the Photochemistry of Aqueous Phenolate-Based Anions Revealed by Extreme Ultraviolet Time-Resolved Photoelectron Spectroscopy

  • Jaydeep Basu1,2
  • Do Hyung Kang1,2,3
  • Neal Haldar1,2
  • Daniel M Neumark1,2,4,5
5 affiliations
  1. 1Department of Chemistry
  2. 2California
  3. 3Sungkyunkwan University
  4. 4Chemical Science Division
  5. 5Lawrence Berkeley National Laboratory
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Abstract

Phenolate (PhO-) is a prototypical chromophore and a recurring motif in photoactive biomolecular systems. Here, we use extreme-ultraviolet time-resolved photoelectron spectroscopy (XUV-TRPES) to probe how para-substitution redirects the photophysics of aqueous 4-nitrophenolate (4NP-) and 4-chlorophenolate (4CP-) anions. In 4NP-, following 400 nm excitation, internal charge reorganization accompanied by nitrogroup torsion forms a stabilized twisted intramolecular charge-transfer (TICT) configuration in 74 fs, efficiently funneling the population through a conical intersection to the ground state within 200 fs. Similar dynamics are seen upon excitation at 240 nm, although the initially excited state is even shorter-lived (40 fs). No hydrated electron production is seen at either wavelength. In 4CP-, following 240 nm excitation of the S2 state, internal conversion to S1 occurs within 120 fs. Chlorine substitution introduces a competing 1πσ* dissociative channel whose potential energy surface intersects S1, but the higher S1/1πσ* crossing barrier relative to 4BP- allows the S1 population to survive long enough (25 ps) for solvent-assisted electron ejection and internal conversion. The dynamics thus resemble those of PhO- rather than the sub-picosecond dissociative relaxation of 4BP-. Taken together with our previous PhO- and 4-bromophenolate (4BP-) measurements, these results reveal how para-substitution across this prototypical series drives the accessibility of competing excited-state dynamical processes, leading to very different photostability and photochemistry.

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Cite

BibTeXRIS
BibTeX
@misc{basu2026substituent,
  title = {{Substituent Effects on the Photochemistry of Aqueous Phenolate-Based Anions Revealed by Extreme Ultraviolet Time-Resolved Photoelectron Spectroscopy}},
  author = {Jaydeep Basu and Do Hyung Kang and Neal Haldar and Daniel M Neumark},
  howpublished = {ChemRxiv},
  year = {2026},
  month = oct,
  doi = {10.26434/chemrxiv.15010331/v1},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010331/v1},
  note = {CC BY},
}
RIS
TY  - UNPB
TI  - Substituent Effects on the Photochemistry of Aqueous Phenolate-Based Anions Revealed by Extreme Ultraviolet Time-Resolved Photoelectron Spectroscopy
AU  - Jaydeep Basu
AU  - Do Hyung Kang
AU  - Neal Haldar
AU  - Daniel M Neumark
PY  - 2026
DA  - 2026/10/13
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15010331/v1
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010331/v1
AB  - Phenolate (PhO-) is a prototypical chromophore and a recurring motif in photoactive biomolecular systems. Here, we use extreme-ultraviolet time-resolved photoelectron spectroscopy (XUV-TRPES) to probe how para-substitution redirects the photophysics of aqueous 4-nitrophenolate (4NP-) and 4-chlorophenolate (4CP-) anions. In 4NP-, following 400 nm excitation, internal charge reorganization accompanied by nitrogroup torsion forms a stabilized twisted intramolecular charge-transfer (TICT) configuration in 74 fs, efficiently funneling the population through a conical intersection to the ground state within 200 fs. Similar dynamics are seen upon excitation at 240 nm, although the initially excited state is even shorter-lived (40 fs). No hydrated electron production is seen at either wavelength. In 4CP-, following 240 nm excitation of the S2 state, internal conversion to S1 occurs within 120 fs. Chlorine substitution introduces a competing 1πσ* dissociative channel whose potential energy surface intersects S1, but the higher S1/1πσ* crossing barrier relative to 4BP- allows the S1 population to survive long enough (25 ps) for solvent-assisted electron ejection and internal conversion. The dynamics thus resemble those of PhO- rather than the sub-picosecond dissociative relaxation of 4BP-. Taken together with our previous PhO- and 4-bromophenolate (4BP-) measurements, these results reveal how para-substitution across this prototypical series drives the accessibility of competing excited-state dynamical processes, leading to very different photostability and photochemistry.
ER  -