Moisture as key for understanding the fluorescence of lignocellulose in wood

The fluorescence behaviour of lignocellulose in Pinus sylvestris L. was studied under the influence of moisture. Fluorescence excitation-emission-matrices (EEMs) of the solid wood surfaces were recorded. Two emission peaks were identified, one attributed to lignocellulose, the other to pinosylvins. The two peaks were successfully modelled with PARAFAC2-deconvolution. Lignocellulose showed excitation-dependent emission. Its emission was quenched and blue-shifted by moisture, while pinosylvin showed none of these properties. The quenching efficiency was proportional to the moisture content (linear Stern-Volmer plot), a phenomenon first demonstrated for wood in this study. Potential mechanisms for the moisture quenching are discussed, with clustering-triggered emission best explaining most of the observed peculiarities. The strong influence of moisture on the fluorescence of pine wood suggests that carbohydrates, or interactions between carbohydrates and lignin, play an important role in lignocellulose fluorescence.