Improving the Efficiency of AIEgen-Based Nondoped Blue Organic Light-Emitting Diode by Rational Isomer Engineering

The development of efficient and stable blue emitters remains a great challenge for organic light-emitting diodes (OLEDs). Herein, a pair of tetraphenylbenzene (TPB)-based isomers of TPB-2AC and iTPB-2AC featuring aggregation-induced emission characteristics are designed and synthesized by attaching two diphenylamine (DPA) moieties and two cyano (CN) groups on its peripheral vicinal or alternating phenyl rings. The nondoped blue OLED with iTPB-2AC as emitting layer exhibits a maximum external quantum efficiency (EQE) of 8.23% with a low operation voltage of 2.8 V, and the performance of the device is comparable with the reported nondoped blue OLEDs based on conventional fluorescent emitters. Whereas, the TPB-2AC-based device shows a low efficiency roll-off effect. Their horizontal dipole orientation and "hot exciton" process were rationalized to play key roles for these performance differences. This work provides a general strategy to achieve high-performance nondoped blue OLED by rational isomer engineering.