New pyrene-based butterfly-shaped blue AIEgens: Synthesis, structure, aggregation-induced emission and their nondoped blue OLEDs

Developing the blue emitters with excellent electroluminescence (EL) performance is crucial for full-color displays and solid-state lighting. Based on the synthetic strategy for exploring highly efficient luminescent solids by constructing aggregation-induced emission (AIE) systems, two new pyrene-based butterfly-shaped blue AIEgens, Py(5,9)BTPE and Py(5,9)BTriPE, have been successfully designed and synthesized by integrating two tetraphenylethylene (TPE) or triphenylethylene (TriPE) groups into pyrene ring. The adoption of the pyrene unit with a large optical bandgap, the use of the TPE or TriPE group with AIE characteristic, the integration of the TPE or TriPE group into pyrene ring at 5,9-positions, and the highly twisted molecular conformations of present AIE systems endow the two compounds with bright blue emission in the solid state. These foregoing features ensure that the new pyrene-based compounds can serve as excellent blue-emitting materials in OLEDs. A non-doped OLED based on Py(5,9)BTPE exhibited a sky-blue emission (Von: 3.2 V) with a CIE coordinates of (0.19, 0.28), a maximum external quantum efficiency (EQEmax) of 3.35%, a current efficiency (CE) of 6.51 cd A−1 with a low efficiency roll-off that represents one of the highest value reported for sky-blue AIE-based OLEDs. An analogous device with Py(5,9)BTriPE as an emitting layer displayed a pure-blue emission (CIE: 0.16, 0.17) with a moderate EQEmax of 1.27% and a CE of 1.63 cd A−1 with a low efficiency roll-off. Furthermore, the EL emissions of the two devices display almost no change with the increasing of the current density, indicating their good color stability.