Facet Engineering‐Modulated Electrochemiluminescence of Reticular Crystalline Nanoemitters

Abstract Electrochemiluminescence (ECL) as a light‐emitting process involves the interfacial charge transfer between the electrochemically generated emitter's intermediate and the coreactant/emitter, critically governed by the emitter's electronic structure and exposed surface state. However, the relationship between the emitter's exposed surface state and ECL performance remains unexplored. Herein, a series of metal‐organic framework (MOF) emitters is synthesized via controlled crystal growth, achieving selective exposure of (001), (100), and (110) facets characterized by micro‐electron diffraction (MicroED) on nanoplate, nanoblock, and nanorod‐shaped MOFs, respectively. Compared to (001) facet, the (110) and (100) facets exhibit 19.5 and 2.4‐fold enhancement of ECL intensity, pronouncing facet‐dependent ECL performance. Notably, the (110) facets exhibit 1088‐fold ECL self‐amplification due to the accumulation of stabilized radicals. Density functional theory calculations identify that the coreactant peroxydisulfate's lateral coordination with Zn(II) on the (110) facet strengthens chemisorption, elongates the O─O bond, and promotes its cleavage to form SO 4 •− radicals, thereby facilitating interfacial charge transfer to generate more excited states for ECL emission. The facet engineering provides a mechanistic guideline for designing crystalline ECL nanoemitters and decoding the fundamentals of ECL techniques.