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

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.