Construction of sp<sup>2</sup> Carbon-Conjugated Covalent Organic Frameworks for Framework-Induced Electrochemiluminescence
Qiu‐Xia Luo, Wei‐Rong Cui, Yajie Li, Yuan‐Jun Cai, Xiang‐Lan Mao, Ru‐Ping Liang, Jian‐Ding Qiu
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.