Color tuning of iridium complexes for organic light-emitting diodes: The electronegative effect and π-conjugation effect

Novel red phosphorescent emitter bis(4-phenylquinazolinato-N,C2′) iridium(acetylacetonate) [(pqz)2Ir(acac)], bis(1-(1′-naphthyl)-5-methylisoquinolinato-N,C2′)iridium(acetylacetonate) [(1-mniq)2Ir(acac)] and bis(1-(2′-naphthyl)-5-methylisoquinolinato-N,C2′)iridium(acetylacetonate) [(2-mniq)2Ir(acac)] have been synthesized and fully characterized. The electronegative effect of (pqz)2Ir(acac) ligand shows almost the same influence as the extended π-conjugation effect of (2-mniq)2Ir(acac). Density functional theory (DFT) was applied to calculate the Kohn–Sham orbitals of HOMOs and LUMOs in the iridium complexes to illustrate the N(1) electronegative atom effect. Finally, lowest triplet state (T1) energies calculated by time-dependent DFT (TDDFT) were compared with the experimental electroluminescent data. The calculated data for the iridium complexes agreed fairly well with experimental data. Electroluminescent devices with a configuration of ITO/NPB/CBP:dopant/BCP/AlQ3/LiF/Al were fabricated. The device using (pqz)2Ir(acac) as a dopant showed deep-red emission with 1931 CIE (Commission International de L’Eclairage) chromaticity coordinates x = 0.70, y = 0.30.

A novel red phosphorescent emitter (bis(4-phenylquinazolinato-N,C2′)iridium(acetylacetonate)) has been synthesized and characterized. Device using this emitter was fabricated and compared with devices using other emitters. The density functional theory (DFT) was applied successfully to illustrate the remarkable N(1) electronegative atom effect of this new emitter.Figure optionsDownload as PowerPoint slide