Photo-oxygenation of meso-Tetraphenylporphyrin Derivatives: the Influence of the Substitution Pattern and Characterization of the Reaction Products

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Abstract
The photo-oxidation reactions of several meso-tetraphenylporphyrins have been studied in order to ascertain the chemical stability of this class of compounds towards singlet oxygen. The 2,6-disubstituted ones showed an excellent stability, whilst this is not the case for other porphyrins with different substitution pattern on the phenyl rings. This parallels what has been previously found using mono-oxygenated donors. The steric effects in protecting the macrocycle seems to be predominant over the electronic ones; even with electron-donating groups in the 2,6-positions, e.g. methoxy groups, the porphyrin macrocycle was not degraded. The reaction on the β-tetrabrominated meso-tetraphenylporphyrin also proceeded easily and yielded a bilinone derivative. The structures of the final products were all elucidated by mass, 1 H and 13 C NMR spectroscopy.