STUDY ON THE MECHANISM OF THE PHOTODEGRAD ATION OF A SPIROOXAZINE - SOLVENT, OXYGEN, DABCO AND PHOTOSENSITIZATION EFFECTS

The purpose of this work is to contribute to a better understanding of the photodegradation process of spirooxazines (SPO), an important cla ss of photochromic compounds. The involvement of molecular oxygen, of electron transfer effect using the amine 1,4-diazabicyclo(2.2.2)octane (DABCO) and solvent effect on the photodegradation of a model compoun d, the -pentamethylspiro[indoline-2,3'-[3H]naphtoxazine], have been in vestigated. The role played by excited species in triplet state on the photodegradation was also studied. The quantum yield of singlet oxyge n formation sensitized by SPO or the corresponding coloured form, the photomerocyanine (PMC), was evaluated : Phi Delta < 0.01. The analysis of our experimental results is consistent with the following interpre tation : the photosensitized formation of activated oxygen species int eracts in a negligible way on the photodegradation. the degradation pr ocess is due almost exclusively to a radical mechanism. The possibilit y of hydrogen atom or electron transfer with the environment, yielding radicals or radical ions, and biradical character of the excited stat es favours the degradation. the DABCO effect on the photodegradation c ould be interpreted through electron-transfer processes : the degradat ion is increased in desaerated solution and decreased in aerated solut ion.