Construction of sp² Carbon-Conjugated Covalent Organic Frameworks for Framework-Induced Electrochemiluminescence

Abstract

Covalent organic frameworks (COFs) are porous crystalline framework materials that are amenable to design and functionalization. Herein, an aggregation-induced emission monomer, 4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl)­tetrabenzaldehyde (ETB), is used as a building block to react with an olefin linkage to construct sp2 carbon-conjugated COFs for exploring their electrochemiluminescence (ECL). The ECL efficiency of ETB immobilized in the COF framework is significantly improved by nearly 100 times without any exogenous co-reactants in aqueous solution, compared with the monomer aggregation state. This framework-induced ECL (FIECL) is attributed to the long-range orderly arrangement of COFs confining the rotation of ETB in the π-conjugated backbone, thereby effectively facilitating the electronic transfer for excited-state generation. Density functional theory calculations prove that the COFs have lower energy bands compared with the monomers, so that electron transfer can be accelerated within frameworks to obtain a much stronger FIECL signal. This FIECL strategy will greatly expand the broad application prospects of COFs in organic optoelectronics.

Aggregation-Induced Emission-Active Nanostructures: Beyond Biomedical Applications

“…Furthermore, the generation of fluorescent photopatterns at the nanoscale using AIEgens for improved performances in applications such as optoelectronics, photonics, sensing, and anticounterfeiting, etc., is another relevant and emerging area to further explore, given that photopatterning can lead to the manipulation of fluorescence properties or amplified fluorescence intensity and response. − On the other hand, in terms of functional materials development, the design and synthesis of AIE-active nanoporous frameworks, such as COFs and MOFs, to improve vapor sensing and optoelectronic application performances remain a hot topic for researchers to pursue. − Particularly, can the pore size of these emissive frameworks be controlled to selectively capture and sense targeted gaseous analytes, giving rise to an amplified fluorescence response? Finally, the use of AIE nanomaterials in photocatalysis for various chemical reactions can be an emerging area, particularly with recent efforts of AIEgens being used in the breakdown of organic pollutants under ambient lighting, hydrogen evolution, and photopolymerization .…”

Structural Isomerism of Covalent Organic Frameworks Causing Different Electrochemiluminescence Effects and Its Application for the Detection of Arsenic

“…To enrich the connotation of the molecular design of the ECL-COF, our group took the lead in employing electron donors (D) and acceptors (A) as building units of COFs and linked them through conjugated CC bonds. The D–A structure inspired the intramolecular charge transfer, thus arousing the ECL from non-ECL monomers; furthermore, the ECL performance can be regulated through the reasonable design of building units. , Despite that significant progress has been created in structure–function relationship under the perspective of monomer and connection types, it still demands further exploration to promote the application of COFs in the ECL field.…”

“…The D−A structure inspired the intramolecular charge transfer, thus arousing the ECL from non-ECL monomers; 19 furthermore, the ECL performance can be regulated through the reasonable design of building units. 20,21 Despite that significant progress has been created in structure−function relationship under the perspective of monomer and connection types, it still demands further exploration to promote the application of COFs in the ECL field. Linkage in COF scaffolds is a non-negligible position, which prospers the properties of COFs, attributing to its influence in the π-conjugated range, planarity, and stability.…”

AIEgen-Based sp2 Carbon-Conjugated Covalent Organic Frameworks with High Stability and Emission for Activatable Imaging and Ferroptosis in Target Tumor Cells

“…Knoevenagel polycondensation reaction has received great attention since fully conjugated sp 2 carbon COF (sp 2 c-COF) has been developed in 2016. , The hydrolysis resistance of the CC linkages and the highly extended π conjugation endow the sp 2 c-COFs with excellent chemical stability and enhanced luminescence. − For example, Jiang’s group reported a family of pyrene-based sp 2 c-COFs with good luminescence property and long-term stability . Although the sp 2 c-COFs are very attractive, the poor reversibility of the formation of CC linkages makes their synthesis quite challenging .…”