Highly efficient non-doped deep-blue organic light-emitting diodes based on pyreneimidazole derivative with external quantum efficiency > 11% and negligible efficiency roll-off

The development of highly efficient deep-blue fluorescent materials applicable in non-doped organic light-emitting diodes (OLEDs) is still an appealing yet challenging task. Herein, we present a rational design of deep-blue material, PyPO, by linking pyreneimidazole (PyI) moiety with diphenyl ether unit through a benzene bridge. A weak charge transfer state between PyI and diphenyl ether in PyPO is observed from the photophysical investigation, and it is provided with the hybridized local and charge transfer (HLCT) feature as indicated by theoretical calculations. The neat thin film of PyPO shows high photoluminescence quantum yield (PLQY) of 70.7% and excellent horizontal dipole ratio of 84.0%, respectively. In particular, the non-doped OLED using PyPO as the active layer exhibits an electroluminescent (EL) emission peak at 448 nm with an impressive maximum external quantum efficiency (EQE) of 11.1% and negligible roll-off at 1000 cd m−2, which is one of the best results among PyI-based deep-blue luminogens. In addition, the red phosphorescent OLED applying PyPO as host achieves a maximum EQE of 31.3% and still remains 28.6% at 1000 cd m−2, demonstrating PyPO is also a suitable phosphorescent host material. The excellent device performance is ascribed to the high-lying reversed intersystem crossing (hRISC) via hot exciton mechanism. These findings may provide new insights for the development of highly efficient deep-blue emitters.