Metal-free, visible-light active and heterogeneous organic photocatalysts offer a more sustainable and environmentally friendly alternative to traditional metal-based catalysts. Here a porous organic hyper-crosslinked polymer, CF-HCP, was successfully synthesized through a facile and cost-effective process. The chemical and structural properties of CF-HCP were fully characterized by using powder X-ray diffraction analysis, Fourier transform infrared spectroscopy, ¹³C solid-state NMR spectroscopy, electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and nitrogen adsorption. The new three-dimensional hyper-crosslinked network possesses a high Brunauer–Emmett–Teller (BET) specific surface area up to 1200 m² g⁻¹ with a pore volume of 0.92 cm³ g⁻¹, and exhibits good thermal, chemical and photochemical stability. Importantly, CF-HCP was found to be a highly effective heterogeneous photocatalyst for a wide range of organic reactions, including the oxidative coupling of primary amines, dehydrogenation of nonactive secondary amine substrates, and selective oxidation of sulfide under visible-light irradiation and using molecular oxygen as a clean oxidant. In particular, mild reaction conditions, ease of product separation by simple filtration, significant recyclability and low cost make this network material an economical and eco-friendly catalyst for the preparation of versatile organic compounds.

The visible-light-driven organic transformation using two-dimensional covalent organic frameworks (2D-COFs) as metal-free heterogeneous photocatalysts is a green and sustainable approach, and it has gained a surge of interest by virtue of the photosensitizer's high crystallinity, abundant porosity, outstanding stability, excellent light-harvesting ability and tunable structure. However, the guiding principle for designing, constructing and selecting COF-based photocatalysts has not been put forward so far. Herein, we contribute a fascinating strategy to guide the acquisition of excellent framework photocatalysts, which is to screen them from a series of isomorphic COFs. As a proof of concept, three new isomorphic pyrene-based 2D-COFs (COF-JLU23, COF-JLU24 and COF-JLU25) with variable linkers were successfully synthesized. In addition to having similar crystallinity and porosity with the same pore size and shape, their absorption, emission, bandgap, energy level, transient photocurrent response and photocatalytic activity could be easily adjusted via configuring different linkers in frameworks. Indeed, COF-JLU24 with electron donor–acceptor characteristics exhibited the best photocatalytic activity among the three isomorphic COFs for C-3 functionalization reactions of indoles, even better than that of the metal-free photocatalyst g-C₃N₄. More importantly, the screened COF-JLU24 as a metal-free photocatalyst still displayed extensive substrate adaptability and excellent recyclability. We anticipate that this strategy will become a robust rule of thumb for fast access to COF-based photocatalysts. In addition, we still highlight that the present study broadens the applied frontier of COF-based photocatalysts.

A robust, cationic, porous organic polymer (C-NSA_Naph-HCP@Br), which exhibits excellent adsorption capacities for organic dyes and Cr₂O₇²⁻ in water with rapid adsorption rates, excellent selectivity and good recyclability, is reported.