Developing green-safe, efficient and recyclable catalysts is crucial for the chemical industry. So far, organic photocatalysis has been proved to be an environmentally friendly and energy-efficient synthetic technology compared with traditional metal catalysis. As a versatile catalytic platform, hyper-crosslinked polymers (HCPs) with large surface area and high stability are easily prepared. In this report, we successfully constructed two porous HCP photocatalysts (TZ-HCPs) featuring s-tetrazine units and surface areas larger than 700 m² g⁻¹ through Friedel–Crafts alkylation reactions. The rational energy-band structures and coexisting micro- and mesopores endow TZ-HCPs with excellent activities to realize the green synthesis of benzimidazoles (28 examples, up to 99% yield, 0.5–4.0 h) in ethanol. Furthermore, at least 21 iterative catalytic runs mediated by TZ-HCP1D were performed efficiently, with 96–99% yield. This study of TZ-HCPs sheds light on the wide-ranging prospects of application of HCPs as metal-free and green photocatalysts for the preparation of fine chemicals.

Various photoactive building blocks can be incorporated into porous organic polymers (POPs). The intrinsic properties, such as various synthetic methods, outstanding inherent porosity, easy tunability, rigid conjugated skeletons and high stability, endow the polymeric organic networks with wonderful potential to act as heterogeneous photocatalytic platforms. However, exploitation of efficient synthetic strategies for metal-free and nontoxic heterogenous photocatalysts, and further insights into the photocatalytic process in organic transformations are still necessary. In this context, we report the concise synthesis of two polymeric frameworks (BTP-CMP and TBTP-CMP) incorporated into bithiophene and thiophthene units via a “bottom-up” strategy. BTP-CMP and TBTP-CMP were employed as heterogeneous photocatalysts in the synthesis of benzimidazoles, and exhibited excellent catalytic activity (up to 98% yield, at least 15 iterative runs). Therefore, the thiophene-embedded networks can serve as stable efficient and recyclable heterogeneous photocatalysts. Additionally, based on the catalytic results of control experiments and the energy band structures of the materials and intermediates, a possible photocatalytic reaction mechanism has been proposed.

It is fascinating to use water as a hydrogen source to enable the hydrogenation of organic molecules in green chemistry. Nevertheless, current light-driven strategies suffer from an expense of reductants for proton reduction due to a high difficulty in overall water splitting. Herein, we have overcome this challenge and report that light-induced overall water splitting is coupled with hydrogenation of aryl bromides by cooperative catalysis between recyclable Pd/g-C₃N₄ and Fe species, which opens up a photocatalytic avenue to use water as both an electron donor and a hydrogen source to enable hydrogenation of aryl bromides, avoiding the use of additional reductants. Moreover, mild conditions, recyclable catalyst systems and the use of visible-light as the energy source make this process greener. The present method also allowed various high value-added deuterated arenes to be effectively synthesized. This work will guide chemists to use water as both an electron donor and a hydrogen source to develop green procedures for the hydrogenation of various organic compounds.

The properties of high stability, inherent porosity, and tunable nature of porous organic polymers (POPs) make these materials ideal catalytic nanoreactors, which can be constructed by incorporating catalytic moieties into the polymer framework. However, direct construction of chiral POPs as metal-free asymmetric catalysts still remains a challenging task. Accordingly, in this article, we report the direct synthesis of a pyrrolidine-based chiral porous polymer (Py-CPP) via a “bottom-up” strategy. Constructed from rigid three-dimensional monomers through the Sonogashira–Hagihara coupling reaction, the Py-CPP material possesses extensive porosity, and readily accessible and uniformly distributed catalytic sites. Specifically, the Py-CPP proves to be an effective heterogeneous organocatalyst for the asymmetric Michael addition of cyclohexanone to nitroolefins in pure water, affording the desired products with high yields (up to 98%) and enantioselectivities (up to 99%).