Photo-oxygenation of meso-tetraphenylporphyrin derivatives: the influence of the substitution pattern and characterization of the reaction products

The photo-oxidation reactions of several meso-tetraphenylporphyrins have be en studied in order to ascertain the chemical stability of this class of co mpounds towards singlet oxygen. The 2,6-disubstituted ones showed an excell ent stability, whilst this is not the case for other porphyrins with differ ent substitution pattern on the phenyl rings. This parallels what has been previously found using mono-oxygenated donors. The steric effects in protec ting the macrocycle seems to be predominant over the electronic ones; even with electron-donating groups in the 2,6-positions, e.g. methoxy groups, th e porphyrin macrocycle was not degraded. The reaction on the beta-tetrabrom inated meso-tetraphenylporphyrin also proceeded easily and yielded a bilino ne derivative. The structures of the final products were all elucidated by mass,H-1 and C-13 NMR spectroscopy. (C) 1998 John Wiley & Sons, Ltd.