Novel iridium complexes containing alkylfluorene functionalized picolinic acid ancillary ligand: Synthesis, optophysics and electroluminescence properties

Two novel green-emitting cyclometalated iridium complexes of (Buppy)2Ir(Tfl-pic) and (Buppy)2Ir(Brfl-pic) were synthesized and characterized, in which Buppy is 2-(4-tert-butylphenyl)pyridine, Tfl-pic is 6-(6′-(9″-octyl-2″,7″-bi(9,9-dioctylfluoren-2-yl)fluoren-9″-yl)hexyloxy) picolinic acid and Brfl is 6-(6′-(2″,7″-di-bromo-9″-octylfluoren-9″-yl)hexyloxy) picolinic acid. Their thermal property, dispersibility and optophysical properties were investigated. Both iridium complexes present intense UV absorption bands and photoluminescence performance in CH2Cl2. Single-emissive-layer polymer light-emitting devices using (Buppy)2Ir(Tfl-pic) and (Buppy)2Ir(Brfl-pic) as a single dopant and a blend of poly(vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole as the host matrix were fabricated. The (Buppy)2Ir(Tfl-pic)-doped devices exhibited a maximum current efficiency of 2.44 cd A−1. As expected, the phase separation and concentration quenching of these iridium complexes in the devices are efficiently suppressed due to appending bulky fluorene derivatives on the picolinic acid unit by a non-conjugated connection.