Protonation of Covalent Organic Framework with Robust Built‐In Electric Field for Dual Electrochemiluminescence Enhancement

Abstract Covalent organic frameworks (COFs) have emerged as promising electrochemiluminescence (ECL) emitters. To achieve the application, herein a dual ECL enhancement strategy is proposed for imine‐linked COF by incorporating bipyridine units and implementing a post‐modification method. After duplex protonation of bipyridine and imine nitrogen facilitated with ascorbic acid as a sacrificial agent, the HCOF Py‐Bpy exhibits a robust built‐in electric field, reduced bandgap, and improved hydrophilicity, resulting in 9.63‐ or 4.11‐fold ECL enhancement with tripropylamine as coreactant compared to COFs without protonation (COF Py‐Bpy ) or with protonated imine nitrogen (HCOF Py‐PB ). The ECL efficiency of 20.85% is 5.27‐ and 2.35‐fold higher than those of COF Py‐Bpy and HCOF Py‐PB , respectively. Density functional theory calculations confirm that the protonated nitrogen in HCOF Py‐Bpy enhances the electron‐withdrawing effect and enables a large dipole moment, which alters charge distribution to strengthen the D‐A effect and thus enhances ECL performance. Utilizing HCOF Py‐Bpy as the emitter, an efficient ECL sensing platform is developed for ultrasensitive detection of iodide (I ‒ ) and iodixanol, which demonstrates a rational post‐synthetic approach to design highly efficient ECL COF emitters, offering broad sensing applications.