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Issue 30, 2014
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Solvent induced conformer specific photochemistry of guaiacol

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Abstract

Using a combination of ultrafast solution- and gas-phase spectroscopies, together with high-level theory calculations, we demonstrate that we are able to track conformer-specific photodissociation dynamics in solution through solvent choice. We reveal this phenomenon in guaiacol (2-methoxyphenol), a key subunit of the natural biopolymer lignin. In cyclohexane, the first electronically excited 1ππ* (S1) state in guaiacol relaxes with a time-constant of τ = 4.5 ± 0.2 ns, mediated through intersystem crossing to lower lying triplet (Tn) states and internal conversion and fluorescence back to the ground state (S0). In contrast, in methanol, a further relaxation channel is also present; the S1 state relaxes with a time-constant of τ = 2.9 ± 0.1 ns, which is now additionally mediated through coupling onto a dissociative 1πσ* (S2) state and subsequent O–H bond fission, evidenced through the appearance of a spectral signature for the guaiacoxyl radical after ∼250 ps. With the aid of complementary calculations, we attribute this to the now absent intramolecular H-bond between OH and OMe moieties, which now favours intermolecular H-bonding to methanol, lowering the barrier to O–H dissociation and facilitating H-atom loss via tunnelling.

Graphical abstract: Solvent induced conformer specific photochemistry of guaiacol

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Article information


Submitted
30 Apr 2014
Accepted
12 Jun 2014
First published
18 Jun 2014

Phys. Chem. Chem. Phys., 2014,16, 16187-16195
Article type
Paper

Solvent induced conformer specific photochemistry of guaiacol

S. E. Greenough, M. D. Horbury, J. O. F. Thompson, G. M. Roberts, T. N. V. Karsili, B. Marchetti, D. Townsend and V. G. Stavros, Phys. Chem. Chem. Phys., 2014, 16, 16187
DOI: 10.1039/C4CP02424A

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