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In this study, we successfully developed two novel vinylene‐linked covalent organic frameworks (COFs) using 2‐connected 3,6‐dimethylpyridazine through Knoevenagel condensation. These COFs featured finely tailored micro‐/nano‐scale pore sizes, high surface areas and stable non‐polar vinylene linkages. Finely resolved powder X‐ray diffraction patterns demonstrated highly crystalline structures with a hexagonal lattice in the AA layer stacking. The resulting one‐dimensional channels possess strong hydrogen‐bond accepting sites arising from the decorated cis‐azo/azine units with two pairs of fully exposed lone pair electrons, endowing the as‐prepared COFs with exceptional water absorption properties. The g‐DZPH‐COF exhibited successive steep water uptake steps starting from low relative pressures (P/PSTA=0.1), with the remarkable water uptake capacity of 0.26 g/g at P/PSTA=0.2 (25 °C), which is the optimal value recorded among the reported COFs. Dynamic vapour sorption measurements revealed the fast kinetics of these COFs, even in the cluster formation process. Water uptake and release cycling tests demonstrated their outstanding hydrolytic stability, durability, and adsorption–desorption retention ability. [ABSTRACT FROM AUTHOR]

Knoevenagel condensation is a powerful tool for the construction of vinylene‐linked covalent organic frameworks. Herein, we established a concise approach to vinylene‐linked COFs by Knoevenagel condensation at the multi‐methyl groups of a pyridine ring through in situ formation of an N‐acyl pyridinium cation in the presence of various acylating reagents. Following this strategy, two vinylene‐linked COFs were constructed using 2,4,6‐trimethylpyridine and multi‐aldehyde‐substituted aromatic derivatives as monomers. The resultant COFs are highly crystalline and assembled into hexagonal lattices with specific surface areas as large as 1915 m2 g−1 (vs. 1972 m2 g−1 of the theoretical value). The stable and abundant pyridine‐decorated regular nanochannels within the COFs allow for catalyzing the esterification of several pharmaceutical intermediates with distinct spatially confined selectivity and recyclability, representing an environmentally friendly catalytic organic transformation. [ABSTRACT FROM AUTHOR]

Embedding heteroatoms into the main backbones of polymeric materials has become an efficient tool for tailoring their structures and improving their properties. However, owing to comparatively harsh heteroatom‐doping conditions, this has rarely been explored in covalent organic frameworks (COFs). Herein, upon aldol condensation of a trimethyl‐substituted pyrylium salt with a tritopic aromatic aldehyde, a two‐dimensional oxonium‐embedded COF with vinylene linkages was achieved, which was further converted to a neutral pyridine‐cored COF by in situ replacement of oxonium ions with nitrogen atoms under ammonia treatment. The two heteroatom‐embedded COFs are conceptually isoelectronic with each other, featuring similar geometric structures but different electronic structures, rendering them capable of catalyzing the visible‐light‐promoted multi‐component synthesis of tri‐substituted pyridine derivatives with good recyclability. [ABSTRACT FROM AUTHOR]

We developed a simple approach to synthesizing ionic vinylene‐linked two‐dimensional covalent organic frameworks (COFs) through a quaternization‐promoted Knoevenagel condensation at three aromatic methyl carbon atoms of N‐ethyl‐2,4,6‐trimethylpyridinium halide with multitopic aromatic aldehyde derivatives. The resultant COFs exhibited a honeycomb‐like structure with high crystallinity and surface areas as large as 1343 m2 g−1. The regular shape‐persistent nanochannels and the positively charged polymeric frameworks allowed the COFs to be uniformly composited with linear polyethylene oxide and lithium salt, displaying ionic conductivity as high as 2.72×10−3 S cm−1. [ABSTRACT FROM AUTHOR]