p–π Conjugation‐Promoted Electrochemiluminescence of Halogenated Covalent Organic Framework Nanoemitters

Abstract Covalent organic frameworks (COFs) are a kind of promising electrochemiluminescence (ECL) crystalline nanoemitters due to their rapid intrareticular charge transfer and predesigned structures. However, the high polarization of heteroatom‐containing linkages impedes the charge transfer within reticular structures. In this study, we construct a series of halogenated COFs nanoemitters composed of terephthalaldehyde ortho‐substitutions and 1,3,6,8‐tetrakis(4‐aminophenyl)pyrene ligands via a covalent halogenation predesign strategy. The incorporation of covalently bonded halogen atoms promotes a dense electron population in carbon–carbon antibonding molecular orbitals, thereby facilitating efficient p–π conjugation within the COF structure. Based on the improved intrareticular charge transfer along carbon skeleton, as evidenced by the Hall effect and terahertz spectroscopy, the brominated COF demonstrates a 49‐fold enhancement in ECL intensity compared to nonhalogenated COF. Furthermore, the performance of four partially brominated COFs establishes a positive correlation between the degree of Br doping and ECL intensity. Beyond the corresponding model compounds, the conjugated frameworks of COFs significantly amplify the halogenation‐induced enhancement effect. This halogenation‐promoted p–π conjugation in reticular skeleton provides a universal strategy to sensitize crystalline nanoemitters for decoding ECL enhancement mechanism.