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

The synthesis and photophysical study of two novel tert ‐butyl modified cyclometalated iridium(III) complexes, i.e., bis(4‐ tert ‐butyl‐2‐phenylbenzothiozolato‐ N ,C 2′ ) iridium(III)(acetylacetonate) [(tbt) 2 Ir(acac)] and bis(4‐ tert ‐butyl‐1‐phenyl‐1 H ‐benzimidazolato‐N,C 2′ ) iridium(III)(acetylacetonate) [(tpbi) 2 Ir(acac)], are reported, their molecular structures were characterized by 13 C NMR, 1 H NMR, ESI‐MS, FT‐IR, and elementary analysis. Compared with their prototypes without tert ‐butyl substituents [(bt) 2 Ir(acac) and (pbi) 2 Ir(acac)], (tbt) 2 Ir(acac) and (tpbi) 2 Ir(acac) both have shortened phosphorescent lifetimes[(tbt) 2 Ir(acac) versus (bt) 2 Ir(acac), 1.1 μs:1.8 μs; (pbi) 2 Ir(acac) versus (tpbi) 2 Ir(acac), 0.8 μs:1.82 μs]. Moreover, (tbt) 2 Ir(acac) has much more improved phototoluminescence quantum efficiencies in CH 2 Cl 2 solution, [(tbt) 2 Ir(acac), 0.51; (bt) 2 Ir(acac), 0.26]. Employing them as dopants, high performance double‐layer PLEDs were fabricated. The (tbt) 2 Ir(acac)‐based and (tpbi) 2 Ir(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.