Synthesis of bicyclometalated iridium complex containing 1,3,4-oxadiazole-based picolinic acid derivative and its optoelectronic properties in polymer light-emitting devices

A picolinic acid derivative bearing an 1,3,4-oxadiazole unit and its bicyclometalated iridium complex (PhOXD)2Ir(BuPhOXD-Pic) were synthesized and characterized, in which BuPhOXD-Pic is 5-(4′-(5″-(4-tert-butylphenyl)-1″,3″,4″-oxadiazol-2″-yl) phenyl) picolinic acid and PhOXD is 2,5-diphenyl-1,3,4-oxadiazole. The optoelectronic properties of this iridium complex were studied in the double-layer polymer light-emitting devices using a blend of poly (9,9-dioctylfluorene) and 5-biphenyl-2-(4-tert-butyl) phenyl-1,3,4-oxadiazole as a host matrix. This complex exhibited a maximum luminance efficiency of 7.7 cd/A at 5.6 mA/cm2 and a peak brightness of 5288 cd/m2 at 153.7 mA/cm2 in the devices. Compared to the (PhOXD)2Ir(Pic) complex, the (PhOXD)2Ir(BuPhOXD-Pic) complex displays better optoelectronic properties in the devices. This study provides a convenient way to improve the optoelectronic properties of iridium complexes by modifying an ancillary ligand of picolinic acid (Pic) with an 1,3,4-oxadiazole unit.