Photoprotective Function of Meso-Substituted Manganese(III) Porphyrin Complexes via Reactive Oxygen Species Scavenging

Three types of meso-substituted manganese(III) porphyrin complexes with phenyl, propyl, and isopropyl substituents were synthesized to examine their photochemical and electrochemical properties. The distortion of the porphyrin rings and redox potentials depended on the substituents. The fluorescence quantum yields of these porphyrins were significantly low, indicating the rapid deactivation of their singlet excited states. Although weak emissions attributed to higher singlet excited states and charge-transfer states were observed, their quantum yields remained low. Redox potential measurements showed the relatively strong photooxidative ability of these porphyrins from a thermodynamic standpoint. However, photosensitized protein oxidation was barely observed. The rapid deactivation of photoexcited states decreases the probability of photochemical reactions including biomolecule oxidation. These porphyrins suppressed the self-oxidation of photo-irradiated 1-benzyl-1,4-dihydronicotinamide and catalyzed the decomposition of hydrogen peroxide. In conclusion, these manganese(III) porphyrin complexes barely showed photooxidation activity toward biomolecules and demonstrated protective action against phototoxic reactions.