Covalent organic frameworks offer a molecular platform for integrating organic units into periodically ordered yet extended 2D and 3D polymers to create topologically well-defined polygonal lattices and built-in discrete micropores and/or mesopores.

We report herein the first enantioselective cycloaddition of vinyl oxetanes, the reaction of which with azadienes provided unprecedented access to ten-membered heterocycles through a [6+4] cycloaddition. By using a commercially available chiral Pd-SIPHOX catalyst, a wide range of benzofuran- as well as indole-fused heterocycles could be accessed in excellent yield and enantioselectivity. A unique Lewis acid induced fragmentation of these ten-membered heterocycles was also discovered.

The development of efficient photocatalysts for N2 fixation to produce NH3 under ambient conditions remains a great challenge. Since covalent organic frameworks (COFs) possess predesignable chemical structures, good crystallinity, and high porosity, it is highly significant to explore their potential for photocatalytic nitrogen conversion. Herein, we report a series of isostructural porphyrin-based COFs loaded with Au single atoms (COFX–Au, X = 1–5) for photocatalytic N2 fixation. The porphyrin building blocks act as the docking sites to immobilize Au single atoms as well as light-harvesting antennae. The microenvironment of the Au catalytic center is precisely tuned by controlling the functional groups at the proximal and distal positions of porphyrin units. As a result, COF1–Au decorated with strong electron-withdrawing groups exhibits a high activity toward NH3 production with rates of 333.0 ± 22.4 μmol g–1 h–1 and 37.0 ± 2.5 mmol gAu –1 h–1, which are 2.8- and 171-fold higher than that of COF4–Au decorated with electron-donating functional groups and a porphyrin–Au molecular catalyst, respectively. The NH3 production rates could be further increased to 427.9 ± 18.7 μmol g–1 h–1 and 61.1 ± 2.7 mmol gAu –1 h–1 under the catalysis of COF5–Au featuring two different kinds of strong electron-withdrawing groups. The structure–activity relationship analysis reveals that the introduction of electron-withdrawing groups facilitates the separation and transportation of photogenerated electrons within the entire framework. This work manifests that the structures and optoelectronic properties of COF-based photocatalysts can be finely tuned through a rational predesign at the molecular level, thus leading to superior NH3 evolution.

Attempts to develop photocatalysts for hydrogen production from water usually result in low efficiency. Here we report the finding of photocatalysts by integrated interfacial design of stable covalent organic frameworks. We predesigned and constructed different molecular interfaces by fabricating ordered or amorphous π skeletons, installing ligating or non-ligating walls and engineering hydrophobic or hydrophilic pores. This systematic interfacial control over electron transfer, active site immobilisation and water transport enables to identify their distinct roles in the photocatalytic process. The frameworks, combined ordered π skeletons, ligating walls and hydrophilic channels, work under 300–1000 nm with non-noble metal co-catalyst and achieve a hydrogen evolution rate over 11 mmol g–1 h–1, a quantum yield of 3.6% at 600 nm and a three-order-of-magnitude-increased turnover frequency of 18.8 h–1 compared to those obtained with hydrophobic networks. This integrated interfacial design approach is a step towards designing solar-to-chemical energy conversion systems.

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