High-efficiency near-infrared fluorescent organic light-emitting diodes with small efficiency roll-off based on AIE-active phenanthro[9,10-d]imidazole derivatives†
The simultaneous realization of high-efficiency and low-cost in fluorescent organic light-emitting diodes (OLEDs) is still a formidable challenge in the deep-red (DR)/near-infrared (NIR) region because of the intrinsic limitation of the energy-gap law and fluorescence quenching effect. Herein, three novel donor–acceptor–donor′ (D–A–D′) fluorophores, PIBz-10-PTZ, PIBz-10P-PTZ and PIBz-3-PTZ, by utilizing phenanthro[9,10-d]imidazole and phenothiazine as the donor and benzothiadiazole as the acceptor are synthesized. Owing to the unilateral steric hindrance between adjacent hydrogen atoms along the horizontal axis, PIBz-3-PTZ possesses a completely planar conformation and fully conjugated structure. PIBz-3-PTZ exhibits a strong DR emission and aggregation induced emission (AIE) property with a high photoluminescence quantum yield of 35% in neat thin films. The nondoped OLEDs achieved a maximum external quantum efficiency (EQE) of 2.02% with an emission peak at 672 nm and a brightness of up to 3403 cd m−2. In addition, the device was able to maintain an EQE of 1.69% at a high luminance of 100 cd m−2, with a low efficiency roll-off of 16%, suggesting that the nondoped device can keep a relatively high efficiency at very high brightness.