Deciphering a volcano-shaped relationship between radical stability and reticular electrochemiluminescence

Abstract

Electrochemiluminescence (ECL) is a light-emitting process in which the stability of electrochemically generated radicals has a crucial impact on the efficiency and durability of excited state generation. Therefore, deciphering a relationship between radical stability and ECL performance is highly appealing. In this work, three sp² carbon-conjugated covalent organic framework (COF) reticular nanoemitters compositing of same pyrene luminophores but different acrylonitrile linkers are designed with progressive electron affinities, named as CN-COF-1, 2, and 3. By precisely modulating the electron affinity of CN-COFs, a volcano relationship between ECL and radical stability is discovered with 78 folds enhancement in ECL intensity. Density functional theoretical calculations indicate that CN-COF-2 exhibits moderate radical stabilization capacity as well as efficient electron transport between the pyrene cores, facilitating ECL generation. Significantly, the appropriate radical stability of CN-COF-2 not only achieves the self-enhanced cathodic ECL but also promotes durability of the ECL intensity. The rational regulation of radical stability paves the way for developing efficient reticular nanoemitters and decoding the ECL fundamentals.