Ternary Acceptor–Donor–Acceptor Asymmetrical Phenanthroimidazole Molecule for Highly Efficient Near‐Ultraviolet Electroluminescence with External Quantum Efficiency (EQE) >4 %.

A new ternary acceptor (A)–donor (D)–acceptor (A) asymmetrically twisted deep‐blue emitting molecule, PPI‐2BI, was synthesized by attaching two electrophilic benzimidazole (BI) units to the C2 and N1 positions of a phenanthroimidazole (PI) donor unit. Profiting from the enhanced D–A electronic coupling, the electron injecting and transporting abilities of the new triangle‐shaped A–D–A molecule are considerably improved and the molecule shows high photoluminescence (PL) and electroluminescence (EL) efficiencies. By using PPI‐2BI as a non‐doped emitting layer (EML), the resulting organic light‐emitting device exhibits emission with color coordinates of (0.158, 0.124) and a maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 4.63 %, 4.98 cd A−1, and 4.82 lm W−1, respectively. Additionally, a simple bilayer device using PPI‐2BI as both the EML and the electron‐transporting layer (ETL) also shows an EQE of 3.81 % with little changes to the color purity. Remarkably, a PPI‐2BI‐based doped device emits efficient near‐ultraviolet EL with color coordinates of (0.154, 0.047) and an EQE of 4.12 %, which is comparable to that of the best reported near‐UV emitting devices. Triangular A–D–A: A new ternary acceptor (A)–donor (D)–acceptor (A) asymmetrically twisted deep‐blue emitting molecule, PPI‐2BI, is synthesized by attaching two electrophilic benzimidazole (BI) units to the C2 and N1 positions of a phenanthroimidazole (PI) donor unit. Profiting from the enhanced D–A electronic coupling, the electron injecting and transporting abilities of the new triangle‐shaped A–D–A molecule are considerably improved and the molecule shows high photoluminescence and electroluminescence efficiencies. [ABSTRACT FROM AUTHOR]