A trimer with thermally crosslinkable vinyl groups, (4-butyl-phenyl)-bis-[4-((4-vinyl-phenyl)-(4-butyl-phenyl)-phenyl-amine)-phenyl]-amine (3-TPA), was synthesized successfully. Differential scanning calorimetry (DSC) thermogram of 3-TPA showed two endothermic processes at 122 and 218 °C at the first heating scan. The endothermic peak at 122 °C corresponds to the melting behavior of 3-TPA and the other at 218 °C seems to be from thermal crosslinking. Thermally cured 3-TPA film at 180 °C for 1 h showed very good solvent resistance and was electrochemically stable. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of cured 3-TPA film was −5.09 and −2.10 eV, respectively. The turn on electric field of PLEDs with cured 3-TPA was 1.37–1.80 MV/cm, which was smaller than that of the device without 3-TPA (2.51 MV/cm). The luminance efficiency and brightness of polymer light-emitting diodes (PLEDs) based on 3-TPA were much higher than that of the PLED without 3-TPA. This is due to that cured 3-TPA has hole injection and transporting property. Among the PLEDs, the device with a 20 nm-thick cured 3-TPA showed the best performance with a maximum efficiency of 1.29 cd/A and a maximum brightnes of 2,500 cd/m2.
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