Fluorescence of Lignin Model Compounds

Lundquist et al. [162] compiled a comprehensive collection of fluorescence data of lignin model compounds. Table 3.10 presents a representative selection of these data. 

Guaiacyl compounds with saturated side chains have a fluorescence maximum of modest intensity at 316 nm. The excitation spectra correspond to the absorbance spectra expected for saturated guaiacyl compounds from the data in Table 3.4. The Si state for simple benzenes is a n-n state, where intersystem crossing is inefficient and fluorescence is expected. The only exception to this behavior was the phenylcou-maran structure, which was only weakly fluorescent. The authors attributed this to a low-lying n-jr state, but no corroboration was given for this assignment. 

4-dimethoxyacetophenone (Fignre 3.18). Okano et al. [163] fonnd that this molecule does not fluoresce and attribnte earlier observed fluorescence [158,164] to the photodegradation prodncts acetoveratrone and guaiacol. 

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