A high thermal stability terpyridine derivative as the electron transporter for long-lived green phosphorescent OLED

A new terpyridine-based compound of 2,2′,7,7′-tetra([2,2':6′,2″-terpyridin]-4′-yl)-9,9′-spirobi[fluorene] (4oTPSF) was designed and synthesized as the electron transporter in organic light-emitting diodes (OLEDs). 4oTPSF exhibited excellent thermal stability with high glass transition temperature (Tg) of 250 °C and melting temperature (Tm) of 460 °C during the thermal measurement. The excellent thermal stability is attributed to the molecular structure, that the steric effect of rigid twisted spirobiflourene and the connected terpyridine (TPY) resulted in a decrease of the intermolecular π-stacking interaction. The studies on electrical characteristics of electron-only devices revealed that 4oTPSF showed high electron-transporting capability, as good as the conventional electron-transporting material (ETM) 1,3,5-tris(N-phenylbenzimid-azol-2-yl-benzene (TPBi). A series of green phosphorescent OLEDs (PhOLEDs) based on bis(2-phenylpyridine)iridium(III)(2,2,6,6-tetramethylheptane-3,5-diketonate) (Ir(ppy)2tmd) or tris[2-(p-tolyl)pyridine]iridium(III) (Ir(mppy)3) as emitter and 4oTPSF as ETM displayed a turn-on voltage of 2.23 V and a maximum power efficiency of 97.8 l m/W and a half-life (T50) of 101, 5680 and 319 390 h at an initial luminance of 10 000, 1000 and 100 cd/m2, respectively. The lifetime of 4oTPSF-based device was twice more than the lifetime of TPBi-based device.