Molecularly engineered π-electron relay enables coreactant-free, oxygen-driven electrochemiluminescence.

Luminol remains a foundational electrochemiluminescence (ECL) emitter, yet its performance is intrinsically restricted by slow electron transfer and the short-lived, diffusive nature of oxygen-derived intermediates. These limitations necessitate external coreactants or catalytic additives, obscuring mechanistic interpretation and reducing operational robustness. Here we demonstrate an unimolecular strategy to reorganize oxygen-driven ECL by covalently integrating phenanthroline and luminol through an imine linkage. The resulting π-extended scaffold forms an internal electron-relay pathway that enhances charge transport, promotes oxygen activation and stabilizes the radical intermediates required for light emission. The hybrid produces strong, coreactant-free ECL under air-saturated conditions, with mechanistic studies confirming a coordinated sequence of intramolecular electron flow, superoxide formation and excited-state generation within a confined redox microdomain. As a proof of concept, the emitter enables sensitive and selective detection of glutathione across a wide concentration range (0.5-1000 μM, detection limit 0.479 μM), with predictable quenching behavior that reflects the hybrid's reorganized oxygen-activation pathway. These findings establish a mechanism-guided molecular blueprint for designing next-generation, oxygen-responsive luminophores in which electronic coupling and structural confinement jointly dictate ECL efficiency.