Azepination‐Induced Frontier Molecular Orbital Delocalization of Multiple Resonance Emitters: Constructing Highly Efficient Narrowband Electroluminescent Materials

Abstract

Abstract Developing diversified construction strategies for high‐color‐purity and efficient multiple resonance thermally activated delayed fluorescence (MR‐TADF) materials is a major strategic demand to meet the requirements of ultra‐high‐definition organic light‐emitting diode (OLED) displays, posing a significant challenge to the design and synthesis of emitters at the molecular level. Herein, a strategy is proposed for azepination‐induced frontier molecular orbital (FMO) delocalization of MR emitters, that is, embedding azepine into the prototype molecule BNCz can effectively improve the π‐conjugation degree and extend the FMO delocalization, thereby constructing a series of long‐wavelength MR‐TADF materials with narrowband emission. Through an intramolecular Scholl reaction, these target molecules with an azepine‐embedded core are afforded by one‐fold heptagonal cyclization of BNCz core and the phenyl ring attached to (aromatic amine‐substituted) aryl precursor. They all exhibit efficient green emission around 520 nm and narrow full‐widths at half‐maximum (FWHMs) of ≤ 37 nm in toluene. OLEDs employing these emitters show excellent electroluminescence (EL) performances, among which m ‐PAz‐BNCz‐based OLED exhibits the optimal EL performances with a peak of 528 nm, a FWHM of 37 nm, Commission Internationale de L'Eclairage (CIE) coordinates of (0.26, 0.70), and a maximum external quantum efficiency (EQE) of 36.2%.