High-triplet-energy host materials containing saturated carbon atom for blue and green phosphorescent OLEDs

Abstract

Two novel bipolar host materials containing saturated sp3-hybridized carbon atom, namely 4-(4-(bis(9-ethyl-9H-carbazol-3-yl)ethyl)phenyl)-1H-1,2,4-triazole (p-TzCCz) and 3-(4-(bis(9-ethyl-9H-carbazol-3-yl)ethyl)phenyl)-1H-1,2,4-triazole (m-TzCCz), are designed and synthesized for blue and green phosphorescence organic light-emitting diodes (PHOLEDs). Carbazole and triazole are selected as the p- and n-type units to construct the bipolar hosts. The presence of the saturated sp3-hybridized carbon atom successfully blocks π-conjugation, leading to extremely high triplet energies of 2.95eV for both p-TzCCz and m-TzCCz, and the distorted molecular configuration endows them high glass transition temperatures of above 100°C. p-TzCCz and m-TzCCz are used as hosts to fabricate PHOLEDs with iridium phosphors as doped emitters. m-TzCCz-hosted blue and green devices exhibited external quantum efficiency as high as 11.89% and 16.09% with color coordinates of (0.14, 0.34) and (0.29, 0.63), respectively. This work may provide an effective strategy to design high triplet energy bipolar host materials for OLEDs application.