Rational molecular design of bipolar phenanthroimidazole derivatives to realize highly efficient non-doped deep blue electroluminescence with CIEy ˂ 0.06 and EQE approaching 6%

Abstract

We report a series of novel phenanthroimidazole (PI) based bipolar deep blue-emitting compounds. The structure-property relationship is systematically studied. A star-shape steric group tetraphenylbenzene (TPB) is substituted to the C2 position of PI, which contributes to high-efficiency deep blue photoluminescence (PL) in solid state; while electron-withdrawing or donating groups are attached to the N1 position to realized tunable charge transfer character for high exciton utilization. Among all the emitters, the non-doped electroluminescent devices based on TPBPPI-PY and TPBPPI-PBI display superior EQE of 5.70% and 5.94% with color coordinates of (0.16, 0.049) and (0.16, 0.059), respectively. These performances are among the best deep blue OLEDs with CIEy < 0.06.