Synthesis and green electrophosphorescence of a novel cyclometalated iridium complex in polymer light-emitting diodes

In this paper, we synthesized a new complex bis(dibenzo[f,h]quinolinato-N,C^2′) iridium(III) acetylactonate ((DBQ)₂Ir(acac)) having a longer conjugate system than bis(2-phenylpyridinato-N,C^2′) iridium(III) acetylacetonate ((PPY)₂Ir(acac)). Interestingly, (DBQ)₂Ir(acac) emits at the same wavelength as (photoluminescence of 530 nm) (PPY)₂Ir(acac). A high-efficiency electrophosphorescent polymer light-emitting diodes was constructed by using (DBQ)₂Ir(acac) as the dopant, and a blend of poly(vinylcarbazole) (PVK) with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD) as the host material. The electroluminescence efficiency of 9.5 cd/A is reported for the device doped with 3 wt% of (DBQ)₂Ir(acac). In this device, the emission from the PVK or PBD host was effectively inhibited with the using (DBQ)₂Ir(acac) . Emission from the dopant molecules in such devices involve localization of the injected electron and hole on the metal-organic center. This can occur by a variety of mechanisms, including Förster and Dexter energy transfer from the host transport material to the dopant, and direct trapping of both electrons and holes on the metal-organic center.