Porphyrin-based covalent organic polymers connected by imine-bonds: efficient and recyclable heterogeneous photocatalysts for the oxidation of thioanisole

Abstract

Three porphyrin-based covalent organic polymers, denoted as MPp–PDA (M = 2H, Zn, and Co), were successfully synthesized through Schiff base condensation between aldehyde-functionalized porphyrin derivatives (MPp) and p-phenylenediamine (PDA). The resulting materials were comprehensively characterized by FT-IR spectroscopy, UV-vis spectroscopy, XPS, SEM, TEM, TGA, and PXRD. Benefiting from their strong light-harvesting ability and high structural stability, the MPp–PDA series were employed as heterogeneous photocatalysts for the selective oxidation of thioanisole. As expected, all three polymers exhibited high conversion, good selectivity, and excellent reusability. Notably, the metal-free H₂Pp–PDA outperformed its metallated counterparts, achieving significantly higher substrate conversion. Furthermore, H₂Pp–PDA demonstrated outstanding cycling stability, maintaining a sulfoxide yield above 90% with nearly 99% selectivity over five consecutive runs. Quenching experiments and EPR measurements further identified that O₂˙⁻ and ¹O₂ are the reactive oxygen species involved in the photocatalytic oxidation process.