The origin of lignin fluorescence

Spruce lignin exhibits fluorescence emission spectra that peaks at approxim ate to 360 nm on excitation at wavelengths ranging from 240 to 320 nm. This can be explained by non-radiative energy transfer from lignin chromophores , that are excited in the wavelength range 240-320 nm, to an acceptor that emits fluorescent Light at approximate to 360 nm. Examinations of lignin sa mples and model compounds suggest that small amounts of phenylcoumarone str uctures in the lignin is a conceivable acceptor. Such structures and stilbe ne structures are formed from structural elements in lignin of the phenylco umaran type on various treatments. The photophysical properties of models f or phenylcoumarone structures [2-(3,4-dimethoxyphenyl)-7-methoxy-3-methyo[b ]-furan, 2-(3,4-dimethoxyphenyl)-3-hydroxymethyl-7-methoxybenzo[b]furan] an d stilbene structures (the E and Z forms of 2-hydroxy-3,3',4'-trimethoxysti lbene) have been examined and are discussed on the basis of crystal structu re determinations. (C) 1999 Elsevier Science B.V. All rights reserved.