B–N–B Embedded multiple-resonance polyaromatic enabling efficient narrowband electroluminescence

Boron/nitrogen (B/N)-doped multi-resonance thermally activated delayed fluorescence (TADF) molecules have emerged as benchmark narrowband emitters for organic light-emitting diodes (OLEDs). However, these emitters face persistent challenges in synthesis and optoelectronic performance, notably aggregation-induced spectral-broadening and inefficient reverse intersystem crossing (RISC). Here, we introduce a molecular design that incorporates a B-N-B covalent-bond into a multiple resonance (MR) framework, synergistically combining narrowband emission of para-positioned B/N with a helically distorted B-N-B configuration that enhances spin-orbit coupling and suppresses molecular aggregations. A lithium-free, stepwise nitrogen-directed borylation enables high-synthesis-yield ( > 80%) targeted emitters, affording deep-blue (452 nm) and greenish (495 nm) TADF emissions with full-width-at-half-maximum of merely 12-14 nm, near-unity photoluminescence quantum yields and accelerated RISC rates ( > 10⁵s^-1). Corresponding OLEDs simultaneously achieve high maximum external quantum efficiencies of 37.9-38.3%, narrow electroluminescence bandwidths of 15-17 nm and decent operational stabilities. This work establishes B-N-B integrated MR-TADF systems as a versatile platform toward high-performance organic optoelectronics.