Regioisomerization-Directed MR-TADF Emitters: Enhanced RISC and Suppressed Aggregation Toward High-Performance Narrowband Blue OLEDs.

The organic light-emitting diode (OLED) performance of multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters is fundamentally constrained by their slow reverse intersystem crossing (RISC) and pronounced aggregation-caused quenching (ACQ). Herein, through regioselective borylation, we design and synthesize a series of blue MR-TADF emitters. The regioisomerization-directed twist configuration synergistically enhances RISC while suppressing ACQ, without compromising spectral purity. The emitter with twist configuration exhibits a remarkably fast RISC rate constant (k) of 7.1 × 10 s, narrowband blue emission with a small full-width at half maxima (FWHM) of 23 nm, and a high photoluminescence quantum yield of 94%. The corresponding OLEDs deliver high-performance narrowband blue emission, with a maximum external quantum efficiency (EQE) of 32.4%, and alleviated efficiency roll-off at high luminance (EQE = 22.2%). Notably, excellent performance is retained even at elevated doping levels (EQE = 29.4% at 20 wt%). This work provides a design paradigm for advancing blue MR-TADF emitters toward practical display technologies.