Twisted Multi-Boron Topological π-Extension Enables Narrowband Deep-Blue Multi-Resonance Thermally Activated Delayed Fluorescence Emitters.

Heteroatom-fused ring systems featuring topological architectures represent a powerful platform for engineering molecular properties. Herein, we report two topology-engineered heteroaromatic emitters, BO-DPAB3 and BO-DPAB4. Through precise modulation of the number, ratio, and spatial arrangement of B, N, and O heteroatoms, a twisted π-conjugated framework with finely tuned electronic structure was constructed. The controllable multi-boron π-extension enables multidirectional electron delocalization while preserving localized excited-state characteristics. The rigid twisted topology minimizes structural relaxation and weakens intermolecular interactions, thereby reducing aggregation-caused quenching and enabling narrowband deep-blue emission at 453 and 449 nm with a full-width at half-maximum (FWHM) of 24 and 20 nm, respectively. Notably, organic light-emitting diode (OLED) devices based on the symmetric tetraboron emitter BO-DPAB4 achieve a maximum external quantum efficiency (EQEmax) of 30.1% and a Commission Internationale de l'Éclairage (CIE) coordinate of (0.138, 0.073). This work establishes twisted multi-boron topological π-extension as an effective molecular design paradigm for developing deep-blue emitters with high efficiency and color purity.