A porous anthraquinone-porphyrin-based covalent organic framework for photocatalytic oxidation of amines to aldehydes

Abstract

A novel anthraquinone-porphyrin-based two-dimensional (2D) COF (AQ-Por-COF) with porous structures was rationally designed and successfully synthesized through a solvothermal condensation reaction between porphyrin amine (Por-NH₂) and anthraquinone bridging aldehyde (AQ-CHO). The resulting COF was characterized using FT-IR, PXRD, UV–vis light adsorption spectra, TGA, SEM and XPS. The pore size distributions of AQ-Por-COF were estimated to be 3.2 nm and in the range of 5–80 nm, centered at –15.7 nm, respectively. In addition, the photocatalytic performances, selectivities and stability of AQ-Por-COF was appraised with the light-induced selective oxidation of benzyl amines to aromatic aldehydes with air as the oxidant in acetonitrile (MeCN). The reaction successfully produced benzaldehydes with an excellent yield of 91 % and high selectivities (>99 %) within 12 h at room temperature. And the order of activities of light LED was found to be lying in the following order: blue > purple > white > red. The experiments also indicated that the conjugation of Por-NH₂ and AQ-CHO is necessary for the enhanced catalytic activity. Furthermore, AQ-Por-COF displayed strong photo-response abilities and suitable photocatalysis potentials, enabling the activation of O₂ to superoxide anions (O₂^•−), the main active oxygen species, which was generated from the activation of oxygen by the separated photogenerated electrons under light irradiation. Finally, the results demonstrated that the insoluble photocatalyst, AQ-Por-COF, exhibited excellent photocatalytic activity, high selective, good recyclability and reusability.