Synthesis and characterization of 9,10-bis(2-phenyl-1,3,4-oxadiazole) derivatives of anthracene: Efficient n-type emitter for organic light-emitting diodes

Abstract

With a general aim to make anthracene derivatives multifunctional (n-type emitter) and also study their suitability as electron transport layers for organic light emitting diodes (OLED), and with a more specific interest to understand the charge transport and packing pattern in the solid state due to the rotating side rings, we report the synthesis and characterization of six novel molecules (5–10) in which the 9 and 10 positions of anthracene have been directly substituted by phenyloxadiazole groups. We have carried out detailed studies of these molecules including photophysical, electrochemical, electroluminescent studies and solid state structure determination through crystallographic techniques. The electron affinity is very high, around 3.1–3.2 eV, and the ionization potential is around 5.9–6.0 eV, comparable to the more commonly used electron transport electroluminescent layer Alq₃. The studies reveal that the new molecules being reported by us, in addition to the high thermal stability, are quite efficient in a two layer unoptimized device with the device structure ITO/α-NPD/5–10/LiF/Al and have an emission in pure green. They also show very high efficiency as electron transport layer in device structure ITO(120nm)/α-NPD(30nm)/Ir(ppy)₃ doped CBP(35nm)/BCP(6nm)/5(28nm)/Al(150nm). From these studies we conclude that the anthracene derivatives also have considerable potential as multifunctional layers and as electron transport layers in OLED.