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Towards understanding photodegradation pathways in lignins : the role of intramolecular hydrogen bonding in excited states
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Young, Jamie D., Staniforth, Michael, Dean, Jacob C., Roberts, Gareth M., Mazzoni, Federico, Karsili, Tolga N. V., Ashfold, Michael N. R., Zwier, Timothy S. and Stavros, Vasilios G. (2014) Towards understanding photodegradation pathways in lignins : the role of intramolecular hydrogen bonding in excited states. The Journal of Physical Chemistry Letters, Volume 5 (Number 12). pp. 2138-2143. doi:10.1021/jz500895w ISSN 1948-7185.
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Official URL: http://dx.doi.org/10.1021/jz500895w
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 1ππ* (S1) state, resulting in a vibrational wavepacket, which is probed by virtue of a dramatic nonplanar → planar geometry change upon photoionization from S1 to the ground state of the cation (D0). Any similar quantum beat pattern is absent in phenol. In syringol, the nonplanar geometry in S1 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 S1, 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.
| Item Type: | Journal Article | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Divisions: | Faculty of Science, Engineering and Medicine > Science > Chemistry | ||||||||
| Journal or Publication Title: | The Journal of Physical Chemistry Letters | ||||||||
| Publisher: | American Chemical Society | ||||||||
| ISSN: | 1948-7185 | ||||||||
| Official Date: | 22 May 2014 | ||||||||
| Dates: |
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| Volume: | Volume 5 | ||||||||
| Number: | Number 12 | ||||||||
| Page Range: | pp. 2138-2143 | ||||||||
| DOI: | 10.1021/jz500895w | ||||||||
| Status: | Peer Reviewed | ||||||||
| Publication Status: | Published | ||||||||
| Access rights to Published version: | Restricted or Subscription Access |
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