Novel green-light-emitting hyperbranched polymers with iridium complex as core and 3,6-carbazole-co-2,6-pyridine unit as branch†

Green-light-emitting hyperbranched polymers with iridium complex as a core and 3,6-carbazole-co2,6-pyridine as a branch were synthesized by Suzuki polycondensation. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels of copolymers reduced gradually with increasing content of 2,6-pyridine units from 10 to 30 mol%. It was found that as a result of the incorporation of the pyridine moiety into the polycarbazole backbone, the device efficiencies could be significantly enhanced. A peak external quantum efficiency (QE), luminous efficiency (LE) and power efficiency (PE) of 13.3%, 30.1 cd/A and 16.6 lm/W were achieved at 5.6 V, respectively, for the device derived from PCzPy10Irppy3. Furthermore, a peak luminance of 82059 cd/m was obtained at 14.0 V. The efficiency loss upon the increase of current density was considerably reduced since the highly branched structures could significantly suppress the interchain interaction between the facial iridium complexes and the self quenching of Ir complexes due to aggregation. The hyperbranched framework using the charge transport balanced 3,6-carbazole-co-2,6-pyridine segment as branch and Ir(ppy)3 complex as core provided a novel molecular design for highly efficient phosphorescent green light-emitting polymers.