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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]

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]

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]

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]

The polarity of a semiconducting molecule affects its intrinsic photophysical properties, which can be tuned by varying the molecular geometry. Herein, we developed a D3h‐symmetric tricyanomesitylene as a new monomer which could be reticulated into a vinylene‐linked covalent organic framework (g‐C54N6‐COF) via Knoevenagel condensation with another D3h‐symmetric monomer 2,4,6‐tris(4′‐formyl‐biphenyl‐4‐yl)‐1,3,5‐triazine. Replacing tricyanomesitylene with a C2v‐symmetric 3,5‐dicyano‐2,4,6‐trimethylpyridine gave a less‐symmetric vinylene‐linked COF (g‐C52N6‐COF). The octupolar conjugated characters of g‐C54N6‐COF were reflected in its scarce solvatochromic effects either in ground or excited states, and endowed it with more promising semiconducting behavior as compared with g‐C52N6‐COF, such as enhanced light‐harvesting and excellent photo‐induced charge generation and separation. Along with the matched energy level, g‐C54N6‐COF enabled the two‐half reactions of photocatalytic water splitting with an average O2 evolution rate of 51.0 μmol h−1 g−1 and H2 evolution rate of 2518.9 μmol h−1 g−1. Such values are among the highest of state‐of‐the‐art COF photocatalysts. [ABSTRACT FROM AUTHOR]

The polarity of a semiconducting molecule affects its intrinsic photophysical properties, which can be tuned by varying the molecular geometry. Herein, we developed a D3h‐symmetric tricyanomesitylene as a new monomer which could be reticulated into a vinylene‐linked covalent organic framework (g‐C54N6‐COF) via Knoevenagel condensation with another D3h‐symmetric monomer 2,4,6‐tris(4′‐formyl‐biphenyl‐4‐yl)‐1,3,5‐triazine. Replacing tricyanomesitylene with a C2v‐symmetric 3,5‐dicyano‐2,4,6‐trimethylpyridine gave a less‐symmetric vinylene‐linked COF (g‐C52N6‐COF). The octupolar conjugated characters of g‐C54N6‐COF were reflected in its scarce solvatochromic effects either in ground or excited states, and endowed it with more promising semiconducting behavior as compared with g‐C52N6‐COF, such as enhanced light‐harvesting and excellent photo‐induced charge generation and separation. Along with the matched energy level, g‐C54N6‐COF enabled the two‐half reactions of photocatalytic water splitting with an average O2 evolution rate of 51.0 μmol h−1 g−1 and H2 evolution rate of 2518.9 μmol h−1 g−1. Such values are among the highest of state‐of‐the‐art COF photocatalysts. [ABSTRACT FROM AUTHOR]

Developing effective synthetic strategies as well as enriching functionalities for sp2‐carbon‐linked covalent organic frameworks (COFs) still remains a challenge. Now, taking advantage of a variant of Knoevenagel condensation, a new fully conjugated COF (g‐C34N6‐COF) linked by unsubstituted C=C bonds was synthesized. Integrating 3,5‐dicyano‐2,4,6‐trimethylpyridine and 1,3,5‐triazine units into the molecular framework leads to the enhanced π‐electron communication and electrochemical activity. This COF shows uniform nanofibrous morphology. By assembling it with carbon nanotubes, a flexible thin‐film electrode for a micro‐supercapacitor (MSC) can be easily obtained. The resultant COF‐based MSC shows an areal capacitance of up to 15.2 mF cm−2, a high energy density of up to 7.3 mWh cm−3, and remarkable rate capability. These values are among the highest for state‐of‐the‐art MSCs. Moreover, this device exhibits excellent flexibility and integration capability. [ABSTRACT FROM AUTHOR]