A scaffold of thermally activated delayed fluorescent polymer dots towards aqueous electrochemiluminescence and biosensing applications

Abstract

To achieve the most efficient, all-exciton-harvesting organic electrochemiluminescence (ECL) for biosensing, aqueous thermally activated delayed fluorescence (TADF)-ECL (aqueous TADF-ECL) was successfully launched to provide a breakthrough for the theoretical ECL efficiency limitation of aqueous fluorescence ECL (aqueous FL-ECL). However, achieving efficient TADF emitters suitable for aqueous TADF-ECL remains challenging. A previous strategy relied on TADF small molecular nanoparticles (NPs). However, the aggregation caused quenching of such TADF molecules within NPs is intense, which renders such NPs inefficient for ECL emission. Herein, we propose developing conjugated polymer dots (Pdots) based aqueous TADF-ECL. Compared to the intrinsic TADF polymer, the Pdots achieve a comparable TADF photophysical properties in water, i.e., the comparable PL spectra, similar PL quantum efficiency (Φ_PL) and intense delayed fluorescent contributions via a fast reverse intersystem crossing rate (k_RISC) of 1.5 × 10⁶ s⁻¹. The resultant relative ECL efficiency (Φ_ECL) of the oxidative-reduction ECL system (C₂O₄²⁻ as the co-reactant) is as high as 11.73% (vs. the Ru(bpy)₃²⁺ counterpart). Additionally, satisfactory dopamine biosensing was accomplished for such TADF-Pdots/C₂O₄²⁻ couple. All those results are combined to highlight the promising potential of such an aqueous TADF-ECL strategy.