PHOTOPEROXIDATION OF UNSATURATED ORGANIC MOLECULES .4. PHOTOSENSITIZED REACTION

The photoperoxidation of 9,10-dimethylanthracene and of 9,10-dimethyl-1,2-benzanthracene sensitized by azulene, anthanthrene, and perylene have been investigated as a function of dissolved oxygen concentration in benzene at 25°. A quantitative analysis of the experimental data, in terms of singlet oxygen participation, provides triplet-state formation efficiencies for the sensitizers anthanthrene and perylene and is consistent with the assignment of the sensitizer triplet state as the sole precursor of the singlet oxygen molecule. The absence of substrate peroxidation in the presence of azulene, excited in its long-wave absorption band, is attributed to an extremely rapid internal conversion of the lowest excited singlet state of this molecule which effectively prevents intersystem crossing to the triplet manifold.