Bipolar hosts and non-doped deep-blue emitters (CIEy = 0.04) based on phenylcarbazole and 2-(2-phenyl-2H-1,2,4-triazol-3-yl)pyridine groups

Abstract

We have designed and synthesized four bipolar materials, TAZ-1Cz, TAZ-2Cz, TAZ-3Cz and TAZ-4Cz, using 2-(2-phenyl-2H-1,2,4-triazol-3-yl)pyridine (TAZ) as an electron-withdrawing group and phenylcarbazole as an electron-donating group. Their rigid molecular structures improve their thermal stability with high glass transition temperatures: 99 °C for TAZ-2Cz, 100 °C for TAZ-3Cz and 103 °C for TAZ-4Cz. Employing TAZ-1Cz, TAZ-2Cz, TAZ-3Cz and TAZ-4Cz as hosts, green phosphorescent organic light-emitting devices (PhOLEDs) with fac-tris(2-phenylpyridine)iridium as an emitter display maximum external quantum efficiencies (EQEs) of 15.8, 15.5, 16.0 and 13.0%, respectively. And blue PhOLEDs hosted by TAZ-1Cz, TAZ-2Cz and TAZ-3Cz achieved maximum current efficiencies of 8.6, 11.0 and 10.6 cd A⁻¹, respectively. Furthermore, non-doped OLEDs using TAZ-1Cz and TAZ-4Cz as emitters exhibit electroluminescence (EL) peaks at 400 and 412 nm with CIE coordinates of (0.16, 0.04) and (0.15, 0.04), which are located in the deep-blue region.