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Keywords:

  • Iridium complexes;
  • Light-emitting diodes, organic;
  • Phosphorescence

Abstract

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.