Novel “hot-exciton” material with high hole mobility for highly efficient deep red OLEDs

Due to the limitation of the energy gap rule, the development of highly efficient deep red hot-exciton material (λEL ≥ 650 nm) remains a great challenge. Here, we designed and synthesized a novel D-A-D type deep red fluorescent molecule, 4,7-bis(10-phenyl-10H-phenoxazin-3-yl)benzo[c][1,2,5]thiadiazole (2PPOXBZ), which is not only efficient deep red emitter but also has high hole mobility (2.56 × 10−3 cm2 V−1 s−1). The excited-state characteristics were investigated through photophysical experiments and theoretical calculations, it had been demonstrated the hot-exciton properties. The optimized non-doped OLED using 2PPOXBZ simultaneously act as a light-emitting layer and the hole transport layer exhibits the maximum external quantum efficiency (EQE) as high as 3.38% with a deep red emission peak at 678 nm, corresponding to the Commission International de L'Eclairage (CIE) coordinates (0.70, 0.30). More importantly, the optimized doped deep red OLED based on 2PPOXBZ as dopant exhibits an EQE up to 7.52% with electroluminescence (EL) peak of 658 nm and CIE coordinates of (0.67, 0.33), which is among the best results based on “Hot-exciton” deep red fluorescent OLEDs at present. The results of this study not only realize highly efficient deep red OLEDs with high color purity but also provide an effective molecular strategy for efficient deep red EL emitters.