High Performance Polymer Electrophosphorescent Devices with tert-Butyl Group Modified Iridium Complexes as Emitters

• Published in: Advanced functional materials 2007-11, Vol.17 (16), p.3319-3325
• Main Authors: Wei, X., Peng, J., Cheng, J., Xie, M., Lu, Z., Li, C., Cao, Y.
• Format: Article
• Language: English
• Subjects: Iridium complexes; Light-emitting diodes; Light‐emitting diodes, organic; organic; Phosphorescence
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200700359

The synthesis and photophysical study of two novel tert‐butyl modified cyclometalated iridium(III) complexes, i.e., bis(4‐tert‐butyl‐2‐phenylbenzothiozolato‐N,C2′) iridium(III)(acetylacetonate) [(tbt)2Ir(acac)] and bis(4‐tert‐butyl‐1‐phenyl‐1H‐benzimidazolato‐N,C2′) iridium(III)(acetylacetonate) [(tpbi)2Ir(acac)], are reported, their molecular structures were characterized by 13C NMR, 1H NMR, ESI‐MS, FT‐IR, and elementary analysis. Compared with their prototypes without tert‐butyl substituents [(bt)2Ir(acac) and (pbi)2Ir(acac)], (tbt)2Ir(acac) and (tpbi)2Ir(acac) both have shortened phosphorescent lifetimes[(tbt)2Ir(acac) versus (bt)2Ir(acac), 1.1 μs:1.8 μs; (pbi)2Ir(acac) versus (tpbi)2Ir(acac), 0.8 μs:1.82 μs]. Moreover, (tbt)2Ir(acac) has much more improved phototoluminescence quantum efficiencies in CH2Cl2 solution, [(tbt)2Ir(acac), 0.51; (bt)2Ir(acac), 0.26]. Employing them as dopants, high performance double‐layer PLEDs were fabricated. The (tbt)2Ir(acac)‐based and (tpbi)2Ir(acac)‐based PLEDs have the maximum external quantum efficiencies of 8.71 % and 10.25 %, respectively, and high EL quantum efficiencies of 5.92 % and 7.21 % can be achieved under high driven current density of 100 mA cm–2. PLEDs fabricated with both the two phosphors have much broadened EL spectra with FWHM of > 110 nm, which afford the feasibility to be used as dopants in white LEDs, and the best doping concentrations of the two complexes in fabrication of PLEDs were optimized. Modifying ligands of iridium complexes with bulky tert‐butyl substituents results in shortened phosphorescent lifetimes, good PL and EL efficiencies. The chelates have much more broadened EL spectra with FWHM of >110 nm compared to their PL spectra (see figure).