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

Abstract 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 RISC ) of 7.1 × 10 5 s −1 , 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 max ) of 32.4%, and alleviated efficiency roll‐off at high luminance (EQE 1000 = 22.2%). Notably, excellent performance is retained even at elevated doping levels (EQE max = 29.4% at 20 wt%). This work provides a design paradigm for advancing blue MR‐TADF emitters toward practical display technologies.