Efficient donor-acceptor host materials for green organic light-emitting devices: non-doped blue-emissive materials with dual charge transport properties.

Comparative optical, electroluminescence and theoretical studies were performed for ()-4'-(1-(4-(2-(1-(4-morpholinophenyl)-1-phenanthro[9,10-]imidazol-2-yl)vinyl)phenyl)-1-phenanthro[9,10-]imidazol-2-yl)-,-diphenyl-[1,1'-biphenyl]-4-amine (SMPI-TPA) and ()-4-(4-(2-(4-(2-(4-(9-carbazol-9-yl)phenyl)-1-phenanthro[9,10-]imidazol-1-yl)styryl)-1-phenanthro[9,10-]imidazol-1-yl)phenyl)morpholine (SMPI-Cz). These compounds show excellent thermal properties, dual charge transport properties and form thin films under thermal evaporation. Blue OLEDs (CIE: 0.16, 0.08) based on SMPI-TPA show efficient device performance ( 6.1%; 5.3 cd A; 5.2 lm W) at low turn-on voltages. Both SMPI-TPA and SMPI-Cz were utilised as hosts for green OLEDs. The devices with SMPI-Cz (30 nm):5 wt% Ir(ppy) exhibit maximum luminance of 20 725 cd m, and and values of 61.4 cd A and 63.8 lm W, respectively. In comparison, devices with SMPI-TPA (30 nm):5 wt% Ir(ppy) exhibit high and values of 65.2 cd A and 67.1 lm W, respectively. Maximum values of 19.6% and 23.4% were obtained from SMPI-TPA:Ir(ppy) and SMPI-Cz:Ir(ppy), respectively. These device performances indicate that the phenanthroimidazole unit is a tunable building unit for efficient carrier injection and it may also be employed as a host for green OLEDs.