Red emitting iridium(III) complexes bearing phenylquinazoline and 1,3,4-oxadiazole amide: Synthesis, crystal structure and photo-electronic properties

Four novel iridium(III) complexes were synthesized, specifically (tfpqz)2Ir(phtfmphoxd) (Ir1), (tfpqz)2Ir (phdtfmphoxd) (Ir2), (tfpqz)2Ir(phtfphoxd) (Ir3), and (tfpqz)2Ir(phpfphoxd) (Ir4), featuring 4-(4-(trifluoromethyl) phenyl) quinazoline (tfpqz) cyclometalated ligand and trifluoromethylated or fluorinated 1,3,4oxadiazole benzamide-based ancillary ligands. Their structural characteristics and optoelectronic properties were thoroughly examined. The crystalline frameworks reveal a pseudo-octahedral arrangement around the iridium center, coordinated by C, N, and O atoms from both cyclometalated and ancillary ligands. Upon illumination in dichloromethane at ambient conditions, the Ir1-Ir4 complexes exhibit red emission maxima at 611, 607, 610, and 602 nm, respectively, accompanied by photoluminescence quantum yields of 14.7%, 19.0%, 21.8 %, and 26.9 %. Additionally, they display narrow full width at half maximum (FWHM) values of 45, 44, 44, and 43 nm, respectively. Photophysical analysis and quantum chemical calculations reveal that their luminescence primarily stems from 3 LC (pi-pi*) transitions involving the cyclometalated ligand tfpqz. Solution processing OLEDs D1-D4, fabricated employing the Ir1-Ir4 complexes as emitters, exhibited peak luminance of 12,454, 11,067, 14,407, and 13,879 cd m-2, and maximum external quantum efficiencies of 7.18 %, 6.58 %, 10.32 %, and 8.42%, respectively. Notably, the devices D1-D4 exhibited mild efficiency roll-off, which can be attributed to the exceptional electron-transporting capabilities imparted by the 1,3,4-oxadiazole amide ancillary ligands integrated within the iridium(III) complexes Ir1-Ir4.