Saturated red-emitting electrophosphorescent polymers with iridium coordinating to β-diketonate units in the main chain

A series of novel copolymers with fluorene-alt-carbazole segments and beta-diketonate moieties coordinating to iridium were synthesized by Suzuki polycondensation, and characterized by H-1 NMR, C-13 NMR, and GPC. In the absorption spectra of the copolymers, metal-to-ligand charge-transfer transitions coming from iridium complex increased in intensity with increasing content of Ir complex in copolymers. The photoluminescence spectra of the copolymers were dominated by emission from the iridium complex with peak at ca. 620 nm even at the feed ratio of the complex as low as 0.5 mol-%. The electrochemical investigation indicated that the incorporation of carbazole and iridium complex units reduce the barrier for both hole and electron injection compared with the polyfluorene. The light-emitting diodes using the copolymers as emission layer under different device configurations were fabricated. The devices with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) show significantly higher external quantum efficiencies than those without PBD. A saturated red-emitting polymer light-emitting diode with emission peak at 628 nm, the maximum external quantum efficiency of 0.6% at the current density (J) of 38.5 mA center dot cm(-2), and the maximum luminance of 541 cd center dot m(-2) at 15.8 V was achieved from the device ITO/PEDOT/PFCzIrpiq3 + PBD (40%)/Ba/Al.