Color tuning of iridium(III) complexes containing 2-phenylbenzothiazole-based cyclometalated ligands for application in highly efficient organic light-emitting diodes

Abstract

By introducing a carbazolyl or diphenylamino substituent into the cyclometalated ligand, replacing the ancillary ligand of acetylacetone into 2-picolinic acid, or employing a homoleptic molecular structure, six complexes (TM1~6) bearing a similar molecular skeleton of yellow-emissive bis(2-phenylbenzo[d]thiozolato-N,C2')iridium (III) (acetylacetonate) (Ir-bt) have been acquired. In despite of their different types of ancillary ligand, or different homoleptic or heteroleptic molecular structures, TM1~3 bearing carbazolyl-modified cyclometalated ligands all emit yellow photoluminescence (PL) with their PL maximum (λPLmax) locating at 555–565 nm. Nevertheless, for TM4~6 bearing diphenylamino-modified cyclometalated ligands, they show red PL emission whose λPLmax = 618–636 nm, which is significantly red-shifted than that of Ir-bt. Note that the PL emission of these diphenylamino-modified iridium chelates can be fine-tuned by alteration on its ancillary ligand, or using a homoleptic structure. By taking advantage of the excellent thermal stability and relatively high PL efficiencies of TM3 and TM6, organic light-emitting diodes devices (OLEDs) using them as phosphorescent guests show relatively high electroluminescence performance. The TM3-based device can emit highly efficient yellow light with CIE coordinates of (0.43, 0.56), a maximum current efficiency (ηLmax) of 54.2 cd·A−1, and a maximum power efficiency (ηPmax) of 48.9 lm·W−1, which is one of the highest reported power efficiency data of yellow PhOLEDs; the TM6-based device can emit orange emission with CIE coordinates of (0.57, 0.42), ηLmax of 18.6 cd·A−1, and ηPmax of 14.3 lm·W−1.