Spectroscopic Studies on Lignin Monomer Analogs: 2-Methoxyresorcinol

Previous spectroscopic studies on prototypical aromatic chromophores of lignin have been performed to gain both an understanding of how lignin interacts with ultra violet light and how changing the location and types of substituents affect its spectroscopy. 2-methoxyresorcinol shares many of the same structural features as these lignin components, but differs in the number and relative positions of the OH and OCH3 units on the ring. Understanding the spectroscopy of 2-methoxyresorcinol can thus contribute to our understanding of the electronic properties of lignin. Many different spectroscopic experiments were carried out, including laser-induced florescence (LIF), dispersed fluorescence (DFL), infrared-ultraviolet hole-burning(IR-UV HB), fluorescence depletion infrared (FDIRS), and microwave spectroscopy. Results for 2-methoxyresorcinol were similar to those of syringol, a molecule previously studied, in its UV properties and IR spectroscopy. Both the LIF and DFL spectra showed profiles indicative of a large geometry change between the ground and excited states, much as was observed with syringol. The IR-UV HB experiment showed that only one conformer of 2-methoxyresorcinol was responsible for the vibronic bands seen in the LIF spectrum, which is verified with density functional theory calculations. FDIRS indicated that both hydroxy groups were forming hydrogen bonds with the oxygen of the central methoxy group. Fermi resonance was also observed in the C-H stretch region of the FDIRS spectrum. The microwave spectrum confirms that the methoxy methyl group points out of plane, accepting 2 H-bonds from the adjacent OH groups. Upon completion of this study, two additional molecules will be studied in a similar fashion in order to gain a better understanding of how the hydroxy and methoxy groups affect the ground and excited states of the aromatic compounds found in lignin