Steric and Electronic Programming of Benzylpyridinium Rotor Substitution for Amplified Aggregated-State Pyrene Electrochemiluminescence and Biosensing

Aggregated-state organic electrochemiluminescence (ECL) emitters are commonly constrained by aggregation-caused quenching (ACQ) and sluggish interfacial charge transfer, restricting their sensing utility. Herein, we simultaneously alleviate both bottlenecks through a steric-electronic co-modulation strategy: pyrene functionalized with electron-deficient benzylpyridinium rotors (Py-xN-BB, x = 1, 2, 4) serves as a unified structural handle to tune molecular packing and electronic structure. The rotor-induced steric bulk attenuates detrimental π−π interactions and enables aggregation-induced emission enhancement (AIEE)-like behavior in Py-4N-BB, while LUMO stabilization, HOMO−LUMO gap narrowing, and reduced interfacial charge-transfer resistance collectively facilitate radical-anion generation and co-reactant-mediated excited-state population. Mechanistically, this substitution-dependent ECL enhancement is rationalized within an ECL quantum yield (ECLQY) framework involving improved charged-intermediate conversion and enhanced excited-state radiative decay. Consequently, Py-4N-BB achieves a relative ECL efficiency of ∼410% versus the Ru(bpy)32+/S2O82− standard. Exploiting this high-efficiency emission and its spectral overlap with Black Hole Quencher 2 (BHQ2) absorbance, we developed a duplex-specific nuclease (DSN)-assisted ECL resonance energy transfer (ECL-RET) biosensor for ultrasensitive miRNA-107 detection. This work establishes a benzylpyridinium-rotor design principle in which an ionic rotor serves as a single molecular lever to co-optimize electronic structure, interfacial kinetics, and photophysical efficiency, offering a principled route to mitigate key limitations of organic ECL emitters.