Construction of organic semiconducting materials with in-plane π-conjugated structures and robustness through carbon-carbon bond linkages, alternatively as organic graphene analogs, is extremely desired for powerfully optoelectrical conversion. However, the poor reversibility for sp 2 carbon bond forming reactions makes them unavailable for building high crystalline well-defined organic structures through a self-healing process, such as covalent organic frameworks (COFs). Here we report a scalable solution-processing approach to synthesize a family of two-dimensional (2D) COFs with trans -disubstituted C = C linkages via condensation reaction at arylmethyl carbon atoms on the basis of 3,5-dicyano-2,4,6-trimethylpyridine and linear/trigonal aldehyde (i.e., 4,4″-diformyl- p -terphenyl, 4,4′-diformyl-1,1′-biphenyl, or 1,3,5-tris(4-formylphenyl)benzene) monomers. Such sp 2 carbon-jointed-pyridinyl frameworks, featuring crystalline honeycomb-like structures with high surface areas, enable driving two half-reactions of water splitting separately under visible light irradiation, comparable to graphitic carbon nitride (g-C 3 N 4 ) derivatives.

Establishing an sp2-carbon-bonding pattern is one of the efficient accesses to various organic semiconducting materials. However, the less-reversible carbon–carbon bond formation makes it still challenging to spatially construct a well-defined organic framework with π-extended two-dimensional (2D) structure through solution process. Here, a Knoevenagel condensation approach to synthesize two new 2D covalent organic frameworks (COFs) connected by unsubstituted carbon–carbon double bond linkages through activating the methyl carbons of a 2,4,6-trimethyl-1,3,5-triazine monomer is presented. The resulting sp2-carbon-linked triazine-cored 2D sheets are vertically stacked into high-crystalline honeycomb-like structures, endowing this kind of COF with extended π-delocalization, tunable energy levels, as well as high surface areas, regular open channels, and chemical stabilities. On the other hand, their microfibrillar morphologies allow for the facile manipulation of thin films as photoelectrodes without additive. Accordingly, such kinds of COF-based photoelectrodes exhibit photocurrents up to ∼45 μA cm–2 at 0.2 V vs RHE as well as rapid charge transfer rates, in comparison with imine-linked COF-based photoelectrodes. In addition, both COFs are applicable for conducting photocatalytic hydrogen generation from water splitting by visible-light irradiation.

Vinylene-bridged covalent organic frameworks (COFs) have shown great potential for advanced applications because of their high chemical stability and intriguing semiconducting properties. Exploring new functional monomers available for the reticulation of vinylene-bridged COFs and establishing effective reaction conditions are extremely desired for enlarging the realm of this kind of material. In this work, a series of vinylene-bridged two-dimensional (2D) COFs are synthesized by Knoevenagel condensation of tricyanomesitylene with ditopic or tritopic aromatic aldehydes. With use of appropriate secondary amines as catalysts, high-crystalline vinylene-bridged COFs were achieved, exhibiting long-range ordered structures, well-defined nanochannels, high surface areas (up to 1231 m 2 g −1 ), and excellent photophysical properties. Under a low loading amount and short reaction time, they enable aerobic photocatalytic transformation of arylboronic acids to phenols with high efficiency and excellent recyclability. This work demonstrates a new functional monomer, tricyanomesitylene, feasible for the general synthesis of vinylene-bridged COFs with potential application in photocatalytic organic transformation, which instigates further research on such kind of material.

Pd nanoparticles were successfully encapsulated inside mesoporous silicalite-1 nanocrystals (Pd@mnc-S1) by a one-pot method. The as-synthesized Pd@mnc-S1 with excellent stability functioned as an active and reusable heterogeneous catalyst. The unique porosity and nanostructure of silicalite-1 crystals endowed the Pd@mnc-S1 material general shape-selectivity for various catalytic reactions, including selective hydrogenation, oxidation, and carbon-carbon coupling reactions.

Polymeric semiconductors are emerging as a kind of competitive photocatalysts for hydrogen evolution due to their well-tunable structures, versatile functionalization, and low-cost processibility. In this work, a series of conjugated porous polymers with substantial cyano-substituted fully sp 2 -carbon frameworks are efficiently synthesized by using electron-deficient tricyanomesitylene as a key building block to promote an organic base-catalyzed Knoevenagel condensation with various aldehyde-substituted arenes. The resulting porous polymers feature donor-acceptor structures with π-extended conjugation, rendering them with distinct semiconducting properties. They possess hierarchically porous structures, nanoscale morphologies, and intriguing wettability. These promising physical characters, finely tailorable by varying the arene units, are essentially relevant to the abundant cynao substituents over the whole frameworks. The as-prepared porous polymers exhibit excellent visible-light-driven photocatalytic activity for water-splitting hydrogen evolution with apparent quantum yield up to 2.0% at 420 nm or 1.9% at 470 nm, among the highest values yet reported for porous polymerbased photocatalysts, also representing the first example of such kinds of catalysts formed through a metal-free-catalyzed carbon-carbon coupling reaction.