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

• DOI: 10.1021/jz500895w
• Publication Date: 2014-05-22T15:57:42Z
• Authors: Jamie D. Young; Michael Staniforth; Jacob C. Dean; Gareth M. Roberts; Federico Mazzoni; Tolga N. V. Karsili; Michael N. R. Ash...; Timothy S. Zwier; Vasilios G. Stavros
• Keywords: Guaiacol

The photoinduced dynamics of the lignin building blocks syringol, guaiacol, and phenol were studied using time-resolved ion yield spectroscopy velocity map imaging. Following irradiation syringol guaiacol with a broad-band femtosecond ultraviolet laser pulse, coherent superposition out-of-plane OH torsion and/or OMe torsion/flapping motions is created in first excited (1)ππ* (S1) state, resulting vibrational wavepacket, which probed by virtue dramatic nonplanar → planar geometry change upon photoionization from S1 to ground state cation (D0). Any similar quantum beat pattern absent phenol. In pronounced enough reduce degree intramolecular H bonding (between groups), enabling atom elimination group. For preserved after excitation, despite S1, prevents O-H bond fission. This behavior affects propensities for forming undesired phenoxyl radical sites these three chromophores provides important insight into their relative "photostabilities" within larger biopolymer.