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We report the first example of a thermally activated delayed fluorescence (TADF) poly(dendrimer), composed of a norbornenyl-derived polymer backbone and dendritic side-chain chromophores comprising 2,3-dicyanopyrazino as the electron acceptor and a first-generation fluorenylcarbazole derivative as the electron donor. The TADF poly(dendrimer) homopolymer, with one dendritic side chain attached to each monomer unit, emitted deep-red light. The emission of the poly(dendrimer) was found to be red-shifted relative to the nonpolymeric doubly dendronized emitter composed of the same components. The simple dendrimer was found to have a solution photoluminescence quantum yield (PLQY) of around 70%. In contrast, the poly(dendrimer) had a PLQY of 9%, which was attributed to intramolecular interchromophore interactions. An interesting feature of the poly(dendrimer) was that oxygen did not quench the TADF emission. We found that the PLQY of the simple dendrimer decreased markedly in neat films, whereas that of the poly(dendrimer) did not, with both having a solid-state PLQY of around 10%. The results suggest that intrapolymer chromophore−chromophore interactions observed in solution for the poly(dendrimer) were similar to the intermolecular chromophore−chromophore interactions of the dendrimer in the solid state. Simple two-layer organic light-emitting diodes comprising nondoped films of the materials and an electron transport layer showed red emission with CIE coordinates of (x > 0.66, y < 0.34). The dendrimer-based device had a maximum external quantum efficiency of 2.4%, which is among the best for solution-processed deep-red emissive TADF-based OLEDs but in a simpler device architecture.
We report a solution-processable dendronised bis-tridentate iridium(iii) complex composed of a bis(imidazolyl)phenyl ligand with a first-generation biphenyl dendron containing t-butyl surface groups and a 2-pyrazolyl-6-phenylpyridine co-ligand.
Controlling the orientation of the emissive dipole has led to a renaissance of organic light-emitting diode (OLED) research, with external quantum efficiencies (EQEs) of >30% being reported for phosphorescent emitters. These highly efficient OLEDs are generally manufactured using evaporative methods and are comprised of small-molecule heteroleptic phosphorescent iridium(III) complexes blended with a host and additional layers to balance charge injection and transport. Large area OLEDs for lighting and display applications would benefit from low-cost solution processing, provided that high EQEs could be achieved. Here, we show that poly(dendrimer)s consisting of a non-conjugated polymer backbone with iridium(III) complexes forming the cores of firstgeneration dendrimer side chains can be co-deposited with a host by solution processing to give highly efficient devices. Simple bilayer devices comprising the emissive layer and an electron transport layer gave an EQE of >20% at luminances of up to ≈300 cd/ m 2 , showing that polymer engineering can enable alignment of the emissive dipole of solution-processed phosphorescent materials.
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