Singlet oxygen-driven photocatalytic oxidation of 1,5-dihydroxynaphthalene by a water-soluble N-confused porphyrin: Mechanism and efficiency optimization

A novel water-soluble N-confused porphyrin, meso-tetrakis(3-methoxy-4-sulfophenyl) N-confused porphyrin (3-NCTMOPPS), was successfully synthesized via sulfonation of 3-NCTMOPP with concentrated H 2 SO 4 at 40 °C in a 72% yield. Structural characterization by 1 H NMR, HR-MS and FTIR confirmed the introduction of sulfonate groups at the para-positions of the phenyl rings, which significantly enhanced water solubility, visible-light absorption, and singlet oxygen generation capacity. The photocatalytic oxidation of 1,5-dihydroxynaphthalene by 3-NCTMOPPS was investigated under white light irradiation, with 5-hydroxy-1,4-naphthoquinone identified as the primary product. The effects of key reaction parameters—including hydrogen peroxide concentration, catalyst dosage, and temperature—were systematically monitored by UV-vis spectroscopy. Optimal conditions (1.6 × 10 -7 mol of 3-NCTMOPPS and 4.9 × 10 -5 mol of H 2 O 2 at 25 °C for 60 min) afforded a maximum conversion of 93.1% for 1,5-dihydroxynaphthalene. Kinetic analysis revealed that the reaction followed first-order kinetics with a rate constant of 0.0245 min -1 . A mechanistic pathway involving singlet-oxygen generation was proposed for this photocatalytic oxidation.