Synthesis, Physical and Electroluminescent Properties of [1,2,4]-Triazolo[4,3 -a ]-pyridine Based Bipolar Red Host Materials and Their Applications in Organic Light-emitting Diodes

Abstract [1,2,4]-Triazolo[4,3- a ]-pyridine based bipolar red host materials, tris(4-([1,2,4]triazolo[4,3- a ]pyridin-3-yl)phenyl)amine ( TPATP ) and tris(4′-([1,2,4]triazolo[4,3- a ]pyridin-3-yl)biphenyl-4-yl)amine ( TPAPTP ) were synthesized for use in red phosphorescent organic light emitting diodes (PhOLEDs). [1,2,4]triazolo[4,3- a ]pyridine enhances the electron transport, while the triphenylamine derivatives enhances the hole transport. Bipolar host materials were prepared by the combination of electron and hole transporting materials. The TPATP and TPAPTP have high triplet energy and appropriate HOMO and LUMO energy levels for charge transportation. Red PhOLED devices based on TPATP and TPAPTP as host materials and Ir(piq) 2 acac as dopant was fabricated, which showed electroluminescent performance with a maximum external quantum efficiencies of 6.04% for TPATP and 9.1% for TPAPTP , maximum power efficiency of 3.71 cd/A for TPATP and 5.58 cd/A for TPAPTP , and maximum luminance of 3.54 cd/m 2 for TPATP and 5.3 cd/m 2 for TPAPTP were obtained.