Tris(cyclometalated) iridium(III) phosphorescent complexes with 2-phenylthiazole-type ligands: Synthesis, photophysical, redox and electrophosphorescent behavior

Tris(cyclometalated) iridium(III) phosphorescent emitters with 2-phenylthiazole-type ligands have been designed and synthesized. Their photophysical properties, electrochemical behavior and electroluminescent (EL) performance can be influenced by introducing fluorine atoms to the phenyl moiety of the thiazole-based ligands. The phosphorescent emission maxima can be shifted from 546 nm to 517 nm by increasing the number of the fluorine atoms attached to the ligands of the iridium(III) complexes. Furthermore, the HOMO levels for these phosphorescent complexes exhibit a gradual decrease from -5.28 eV to -5.59 eV with the introduction of fluorine atoms. Owing to the character of their electronic structures, the phosphorescent emitters are preferentially excited by means of a host-guest energy-transfer process in the organic light-emitting diodes (OLEDs). Accordingly, their EL performance is strictly restricted by the triplet energy level difference between the phosphorescent dopant and the host materials. The thiazole-based cyclometalated iridium(III) triplet emitters can exhibit maximum EL efficiencies with η_ext = 7.87 %, η_L = 23.62 cd A^-1 and η_p = 13.46 lm W^-1. Tris(cyclometalated) iridium(III) phosphorescent complexes with 2-phenylthiazole-type ligands have been developed. Their photophysical, redox and electrophosphorescent properties were characterized to address the light-emitting characteristics of the triplet emitters bearing thiazole-based ligands.