Issue 6, 2013

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

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–S0 excitation 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.

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

Supplementary files

Article information

Article type
Edge Article
Submitted
31 Jan 2013
Accepted
06 Apr 2013
First published
08 Apr 2013

Chem. Sci., 2013,4, 2434-2446

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

T. N. V. Karsili, A. M. Wenge, S. J. Harris, D. Murdock, J. N. Harvey, R. N. Dixon and M. N. R. Ashfold, Chem. Sci., 2013, 4, 2434 DOI: 10.1039/C3SC50296A

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