O-H bond fission in 4-substituted phenols: S1 state predissociation viewed in a Hammett-like framework

Tolga N. V. Karsili, Andreas M. Wenge, Stephanie J. Harris, Daniel Murdock, Jeremy N. Harvey, Richard N. Dixon, Michael N. R. Ashfold*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

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Abstract

The photofragmentation dynamics of various 4-substituted phenols (4-YPhOH, Y = H, MeO, CH3, F, Cl and CN) following π* ← π excitation to their respective S1 states have been investigated experimentally (by H Rydberg atom photofragment translational spectroscopy) and/or theoretically (by ab initio electronic structure theory and 1- and 2-D tunnelling calculations). Derived energetic and photophysical properties such as the O–H bond strengths, the S1–S0excitation energies and the S1 predissociation probabilities (by tunnelling through the barrier under the conical intersection between the S1(11ππ*) and S2(11πσ*) potential energy surfaces in the RO–H stretch coordinate) are considered within a Hammett-like framework. The Y-dependent O–H bond strengths and S1–S0 term values are found to correlate well with a simple descriptor of the electronic perturbation caused by the aromatic substituent Y (the Hammett constant, σ+p). We also identify clear correlations between σ+p and the probability of a photochemical process (predissociation). Such a finding is unsurprising, given that Y substitution will perturb the entire potential energy landscape, but appears not to have been demonstrated hitherto. The predictive capabilities of this approach are explored by reference to existing energetic data for larger 4-substituted phenols like 4-ethoxyphenol, tyramine, L-tyrosine and tyrosine containing di- and tri-peptides.
Original languageEnglish
Pages (from-to)2434-2446
Number of pages13
JournalChemical Science
Volume4
Issue number6
Early online date8 Apr 2013
DOIs
Publication statusPublished - 2013

Keywords

  • THRESHOLD IONIZATION SPECTROSCOPY
  • HIGH-RESOLUTION
  • PARASUBSTITUTED PHENOLS
  • P-CYANOPHENOL
  • SUBSTITUENT CONSTANTS
  • NEAR-UV PHOTOLYSIS
  • PHOTOELECTRON-SPECTROSCOPY
  • PHOTOFRAGMENT TRANSLATIONAL SPECTROSCOPY
  • THEORETICAL CALCULATIONS
  • FLUORESCENCE SPECTROSCOPY

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