Elucidating Orbital Delocalization Effects on Boosting Electrochemiluminescence Efficiency of Carbon Nitrides

Abstract Highly efficient inter‐conversion of different types of energy is the core of science and technology. Among them, electrochemiluminescence (ECL), an emission of light excited by electrochemical reactions, has drawn attention as a powerful tool across diverse fields in addressing global energy, environment, and health challenges. Nonetheless, the ECL efficiency (Φ _ECL ) of most luminophores in aqueous solutions is low, significantly hampering their broad applications. Along this line, developing ECL luminophores with high Φ _ECL and understanding the associated intrinsic factors is highly envisioned. Herein, taking carbon nitride (CN) with rigid 2D backbones as an emerging model luminophore, it is reported that the orbital delocalization is a unified and quantifiable factor for its Φ _ECL . Behind the complicated transformation of molecular structures of cyano‐terminal groups and triazine/heptazine basal frameworks, the orbital delocalization of CN is found to be generally improved at an elevated condensation temperature. Such intrinsic evolution in electronic structure favored the electron injection in excitation and follow‐up photon emission in ECL for CN. As a result, the cathodic Φ _ECL of CN is remarkably improved to a new milestone of 24‐fold greater than the previous record.