Nitrogen/Carbonyl Multiple Resonance Emitters Based on Nitrogen Doped 5/6/7‐Membered Rings

Comprehensive Summary The development of high‐performance multi‐resonance (MR) emitters has been booming vigorously in recent years, driven by the enormous demand for organic light‐emitting diodes (OLEDs). Typically, MR emitters incorporate electron‐withdrawing groups (EWGs) and electron‐donating groups (EDGs), which are conducive to reducing the energy gap between the excited triplet (T 1 ) and singlet (S 1 ) states. Among the diverse family of MR emitters, quinolino[3,2,1‐ de ]acridine‐5,9‐dione (QAO) cores have garnered increasing attention due to their excellent molecular modularity and tunable electronic properties. However, most reported MR emitters based on the QAO core feature benzenoid six‐membered rings. Five‐ and seven‐membered ring‐containing QAO‐based MR emitters remain scarce, primarily due to the synthetic challenges involved, despite their potential to exhibit intriguing anti‐aromatic properties. Herein, three novel nitrogen/carbonyl‐based MR emitters ( NE‐1 , NE‐2 , and NE‐3 ) with nitrogen‐doped 5/6/7‐membered rings were successfully synthesized and fully characterized via thermal analysis, cyclic voltammetry, theoretical calculations, and OLED device tests. Notably, the seven‐membered nitrogen/carbonyl rings in these emitters were found to possess strong anti‐aromaticity, as evidenced by large positive Nucleus‐Independent Chemical Shift (NICS) values: 15.09 for NE‐1 , 7.61 for NE‐2 , and 18.05 for NE‐3 . In contrast, the six‐membered nitrogen/carbonyl rings exhibited much weaker anti‐aromaticity. All three emitters emitted green light in OLED devices, with electroluminescent (EL) peaks at 491 nm ( NE‐1 ), 484 nm ( NE‐2 ), and 530 nm ( NE‐3 ), respectively. Among them, NE‐3 achieved the optimal device performance, with a maximum current efficiency (CE m ₐₓ) of 8.5 cd·A –1 , a maximum power efficiency (PE m ₐₓ) of 8.8 lm·W –1 , a maximum external quantum efficiency (EQE m ₐₓ) of 2.2%, and Commission Internationale de l'Éclairage (CIE) coordinates of (0.30, 0.65).