Synthesis of bipolar hosts based on carbazole moiety for red phosphorescent OLEDs

New host materials, 2,7-di-tert-butyl-9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole (TRZPCz) and 2,7-di-tert-butyl-9-(5′-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1’:3′,1’’-terphenyl]-2’-yl)-9H-carbazole (TRZTPCz), were synthesized based on a carbazole core. A terphenyl (TP) group was introduced as a linker to induce steric hindrance and suppress molecular rotation. TRZTPCz exhibited a higher triplet energy level (T1 = 2.80 eV) and a smaller singlet–triplet energy gap (ΔEST = 0.26 eV) compared to TRZPCz. In red phosphorescent organic light-emitting diodes (OLED) devices using TRZTPCz as the host, the device achieved a maximum external quantum efficiency (EQE) of 6.11%. In both non-doped and doped devices, TRZTPCz demonstrated favorable electroluminescence (EL) performance.