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.