PHOTOCHEMICAL STUDIES ON A PHENOLIC PHENYLCOUMARONE LIGNIN MODEL MOLECULE IN RELATION TO THE PHOTODEGRADATION OF LIGNOCELLULOSIC MATERIALS .2. PHOTOPHYSICAL AND PHOTOCHEMICAL STUDIES

The structure of the photoproducts obtained by irradiation of a phenyl coumarone molecule PCO, model of the photodegradation of lignin, being established, the mechanism of their formation was approached by fluor escence and flash photolysis techniques, low temperature absorption sp ectroscopy in rigid matrix, and continuous irradiation in solution and in the solid state. Some evidence was given for the formation of a ph enoxy radical leading either by oxidoreductive processes to the format ion of a catechol IR3, or by coupling with the starting phenol to the generation of a cyclobutane radical dimer, prone to be transformed int o stilbene phenoxy radical by retro ''2 pi + 2 pi'' reaction. It was p roposed that the oxidation of the latter could give the very coloured quinone methide IR1 or the alpha-carbonylstilbenol IR2. The singlet ma nifold appears to be the main pathway of the production of IR1, IR2 an d IR3 which are formed in the presence of ground state oxygen.