Luminescence Comparison of Homoleptic and Heteroleptic 6-membered Iridium(III) Complexes

The new iridium complexes, heteroleptic Ir(4-Me-2,3-dpq)2(LX) (4-Me-2,3-dpq = 4-methyl-2,3-diphenylquinolinato ligand; LX = 2-(2-hydroxyphenyl)benzoxazolate (BOX) and 2-(2-hydroxyphenyl)benzothiazolate (BTZ)) and homoleptic Ir(LX)3, were synthesized and their luminescence properties were investigated. The lithium salts of the ligands, BOX and BTZ, were previously applied to OLED as the blue fluoresecent dyes. These ligands can form 6-membered metallacycles with the metal center. Herein, BOX and BTZ were introduced as ligands to the iridium complexes for possible application to phosphorescent OLEDs. According to the previously reported literature, the ancillary ligand could have a profound effect on the emitting color of its complexes depending on the relative orbital energy levels of the main ligands (CˆN) and the ancillary ligand(LX). For the heteroleptic iridium complexes, 4-Me-2,3-dpq which could form a 5-membered metallacycle with the iridium center was introduced as a main ligand. We compared the luminescence and stability of the homoleptic and heteroleptic iridium complexes with respect to their structures. We investigated photoabsorption and photoluminescence properties of the iridium complexes and studied their band gaps with cyclic voltammetry. The emitting colors and the luminous efficiencies of the complexes were compared to find the involvement effect of the five- and six-membered rings in the complexes.