Abstract
A series of compounds are designed and synthesized by incorporating electron-donating group and electron-withdrawing groups into one molecule. Their thermal, photophysical and electrochemical properties can be finely tuned through the different collocation. These materials have the following advantages: i) high triplet energies in the range of 2.96-3.01 eV; ii) HOMO/LUMO levels of the compounds mainly depend on the electron-donating and electron-withdrawing groups, respectively; iii) bipolar transporting feature is demonstrated by hole-only and electron-only devices. These advantages make these materials as ideal universal hosts for multicolor (R-G-B) phosphorescent OLEDs with high efficiencies. In particular, the devices achieve maximum external quantum efficiencies of 24.4 % (28.0 lm/W) at CIE (0.13, 0.20) for blue, 27.5 % (112.4 lm/W) at CIE (0.28, 0.64) for green, and 18.0 % (22.8 lm/W) at CIE (0.67, 0.33) for red electrophosphorescence. Finally, we fabricated a three-color based phosphorescent WOLED: FIr6, Ir(ppy)3 and (piq)2Ir(acac) were doped into the bipolar host as the single emitting layer. Device W4 achieved maximum external quantum efficiencies of 13.3 % (23.8 lm/W) for white electro -phosphorescence. Additionally, CIE coordinate of the device is (0.34, 0.42) with the color-rendering index (CRI) of 84. The high performance of R/G/B/W devices can be attributed to the suitable triplet energy gap and bipolar character.