Novel 12,12-Dimethyl-7,12-dihydrobenzo[a]acridine as a Deep-Blue Emitting Chromophore for OLEDs with Narrow-Band Emission and Suppressed Efficiency Roll-Off

The fabrication of deep-blue emitting materials with high color purity is crucial for the realization of ultra-high-definition display technology based on organic light-emitting diodes (UHD-OLEDs). However, the intrinsic broad-band emission of organic emitters makes this task difficult. In this study, 9,9-dimethyl-9,10-dihydroacridine (DMAC) was fused with an additional phenyl moiety to design rigid 12,12-dimethyl-7,12-dihydrobenzo[a]acridine (DMBA) as a novel chromophore for design of deep-blue narrow-band emission emitters. Furthermore, functionalization of DMBA with a cyano group yielded two bipolar emitters, viz. 12,12-dimethyl-7-phenyl-7,12-dihydrobenzo[a]acridine-3-carbonitrile (BACN) and 4-(12,12-dimethyl-7-phenyl-7,12-dihydrobenzo[a]acridin-3-yl)benzonitrile (BAPCN). The single-crystal structure analysis confirmed that BACN and BAPCN featured large rigid planar structures. The photophysical study demonstrated that both emitters exhibited narrow-band emissions in the deep-blue region with high fluorescence quantum efficiencies. The doped device based on BACN demonstrates an efficient deep-blue emission that peaks at 437 nm with a small full width at half maximum of 41 nm/0.26 eV and a corresponding Commission International de L’Eclairage (CIE) coordinate of (0.153, 0.049). Meanwhile, their non-doped devices show lower turn-on voltage and smaller external quantum efficiency (EQE) roll-off, particularly in the BAPCN-based non-doped device with a negligible EQE roll-off of only 4.4% at 10000 cd m-2, as a consequence of their good/balanced carrier transporting properties. The optoelectronic properties of these emitters substantiate their potential as deep-blue emitting materials for OLED applications.