Towards Understanding Photodegradation Pathways in Lignins: The Role of Intramolecular Hydrogen Bonding in Excited States

Jamie D. Young, Michael Staniforth, Jacob C. Dean, Gareth M. Roberts, Federico Mazzoni, Tolga N. V. Karsili, Michael N. R. Ashfold, Timothy S. Zwier, Vasilios G. Stavros*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

19 Citations (Scopus)
443 Downloads (Pure)

Abstract

The photoinduced dynamics of the lignin building blocks syringol, guaiacol, and phenol were studied using time-resolved ion yield spectroscopy and velocity map ion imaging. Following irradiation of syringol and guaiacol with a broad-band femtosecond ultraviolet laser pulse, a coherent superposition of out-of-plane OH torsion and/or OMe torsion/flapping motions is created in the first excited (1)pi pi* (S-1) state, resulting in a vibrational wavepacket, which is probed by virtue of a dramatic nonplanar -> planar geometry change upon photoionization from S-1 to the ground state of the cation (D-0). Any similar quantum beat pattern is absent in phenol. In syringol, the nonplanar geometry in S-1 is pronounced enough to reduce the degree of intramolecular H bonding (between OH and OMe groups), enabling H atom elimination from the OH group. For guaiacol, H bonding is preserved after excitation, despite the nonplanar geometry in S-1, and prevents O-H bond fission. This behavior affects the propensities for forming undesired phenoxyl radical sites in these three lignin chromophores and provides important insight into their relative "photostabilities" within the larger biopolymer.

Original languageEnglish
Pages (from-to)2138-2143
Number of pages6
JournalJournal of Physical Chemistry Letters
Volume5
Issue number12
Early online date22 May 2014
DOIs
Publication statusPublished - 19 Jun 2014

Keywords

  • VIBRATIONAL WAVE-PACKETS
  • MASS-SPECTROMETRY
  • IONIZATION SPECTROSCOPY
  • DYNAMICS
  • PHENOL
  • METHOXYPHENOL
  • PHOTOELECTRON
  • BIOSYNTHESIS
  • FLUOROPHENOL
  • BIOMOLECULES

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