Solution processible imidazole-based iridium dendrimers with oligocarbazole for nondoped phosphorescent OLEDs
作者:Mingming Zhang、Xuefei Li、Shumeng Wang、Junqiao Ding、Lixiang Wang
DOI:10.1016/j.orgel.2019.02.017
日期:2019.5
By introducing t-butyl- or methoxyl-containing oligocarbazole into the periphery of tris(mesityl-2-phenyl-1H-imidazole)iridium (III) [Ir (mpim)(3)], two novel imidazole-based Ir dendrimers Bu-t-D2-Ir (mpim)(3) and MeO-D2-Ir (mpim)(3) have been designed and synthesized through a convenient post-dendronization route. Due to the effective encapsulation, the intermolecular interactions and thus luminescence quenching in solid states is found to be gradually reduced following a sequence of Ir (mpim)(3) > MeO-D2-Ir (mpim)(3) > Bu-t-D2-Ir (mpim)(3). Compared with the bare Ir (mpim)(3) core (Phi(PL) = 0.38 and tau = 0.26 mu s), accordingly, the film photoluminescence quantum yield and excited state lifetime are improved to 0.54 and 0.39 mu s for MeO-D2-Ir (mpim)(3) and 0.88 and 1.09 mu s for Bu-t-D2-Ir (mpim)(3). When these developed Ir dendrimers are adopted as the emitting layer alone, Bu-t-D2-Ir (mpim)(3) achieves an excellent nondoped device performance, revealing a maximum current efficiency as high as 35.7 cd/A (13.2%, 37.4 lm/W) together with Commission Internationale del_Eclairage coordinates of (0.21, 0.45). Even at a high luminance of 1000, 5000 and 10000 cd/m(2), it still remains to be 27.8, 24.7 and 21.8 cd/A, respectively, indicative of the gentle efficiency roll-off. The result clearly demonstrates the great potential of imidazole-based Ir dendrimers used for efficient nondoped phosphorescent organic light-emitting diodes.