Novel difluorenyl substituted 1,3,5-triazine and carbazole based bipolar host materials with high thermal stability for efficient green phosphorescent organic light-emitting diodes (PhOLEDs)

Abstract

In this work, two novel compounds 9-(4'-(4,6-bis(9,9-dimethyl-9H-fluoren-2-yl)-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-4-yl)-9H-carbazole (TPBDF-Cz1) and 3-(4-(4,6-bis(9,9-dimethyl-9H-fluoren-2-yl)-1,3,5-triazin-2-yl)phenyl)-9-phenyl-9H-carbazole (TPBDF-Cz2) were synthesized and fully characterized by taking advantage of carbazole, 1,3,5-triazine and fluorene groups. Both materials exhibit extremely excellent thermal properties, appropriate HOMO and LUMO energy levels and high triplet energy. With the beneficial physical behaviors through measuring their optical and electrochemical properties, green PhOLEDs with the two materials acting as host were designed and fabricated. Both devices reveal a low turn-on voltage of 3.0 V and good electroluminescence performance owing to the balanced hole and electron transport mobilities. Besides, it was found that the TPBDF-Cz1-based device is slightly more efficient than the TPBDF-Cz2-based one because of higher carrier transport ability of TPBDF-Cz1. The relevant results indicate TPBDF-Cz1 opens up a new perspective for designing hosts for high performance PhOLEDs.