Novel ZnII complexes of 2-(2-hydroxyphenyl)benzothiazoles ligands: electroluminescence and application as host materials for phosphorescent organic light-emitting diodes

Abstract

A group of novel zinc complexes containing 2-hydroxyphenylbenzothiazole (BTZ) ligands were designed and synthesized, in which different substituents (OCH₃, CH₃, F, CF₃, COOCH₂CH₃) were attached at the 6-position of the benzothiazole ring in the BTZ ligands. Both photoluminescence (PL) and electroluminescence (EL) behaviors of these zinc complexes were investigated. The emission colors of these zinc complexes were readily tuned from bluish-green to yellow by simply varying the substituent, with strong electron-withdrawing substituents being favorable for longer-wavelength fluorescence. Efficient EL was obtained when these zinc complexes were used as non-doped emitting layers in organic light-emitting diodes (OLEDs). Furthermore, these zinc complexes were proved to be capable of acting as triplet hosts for iridium phosphor in red phosphorescent OLEDs. A high external quantum efficiency of 17.5% was realized for the red phosphorescent OLED with the present zinc complexes as hosts and tris(2-phenylisoquinoline)iridium as doped emitter, which is greatly enhanced compared to that (12.6%) of the device with the traditional 4,4′-bis(N-carbazoly)biphenyl (CBP) as host. The present study successfully exploited novel zinc complexes as electron-transporting host materials for phosphorescent OLEDs.