A porphyrin-based covalent organic framework with an aminoxyl radical for deep-red light photocatalysis

Abstract

Porphyrin is a highly conjugated tetrapyrrolic macrocycle that exhibits well-defined symmetry and pronounced photoredox properties. By using porphyrin as the knot, two-dimensional (2D) covalent organic frameworks (COFs) effectively integrate their inherent molecular photoactivity into extended, ordered porous networks. Herein, Por-sp²c-COF, a porphyrin-based 2D COF, is constructed via Knoevenagel condensation between 5,10,15,20-tetrakis(4-benzaldehyde)porphyrin and 1,4-phenylenediacetonitrile. The vinylene linkage endows Por-sp²c-COF with an enhanced absorption range across the visible spectrum, thereby enabling efficient deep-red light photocatalysis. Under deep-red light irradiation, a catalytic amount of the aminoxyl radical 9-azabicyclo[3.3.1]nonane N-oxyl (ABNO) markedly enhances the reaction efficiency of Por-sp²c-COF in the selective oxidation of organic sulfides. Mechanistic studies reveal that ABNO facilitates charge separation and transfer, thereby enhancing the generation of superoxide, the predominant reactive oxygen species. For the selective oxidation of sulfides, Por-sp²c-COF/ABNO photocatalysis offers both excellent recyclability and broad substrate applicability. Porphyrin-based COFs provide access to the challenging deep-red light window for highly efficient and selective photocatalysis.