A red emissive poly(dendrimer) for solution processed organic light-emitting diodes

A red-emissive poly(dendrimer) comprised of a norbornenyl-derived polymer backbone with a phosphorescent dendrimer side-chain has been prepared by ring-opening methathesis polymerization with a number average molecular weight of 164 kDa and a dispersity of 2.4. The dendrimer side-chain had a heteroleptic iridium(III) complex core containing two 2-phenylpyridyl ligands and one 2-(thiophen-2-yl)quinoline ligand. The 2-phenylpyridyl ligands had first generation fluorenylcarbazole dendrons with n-propyl surface groups attached and the 2-(thiophen-2-yl)quinoline ligand was linked to the polymer backbone. In spite of the presence of the two 2-phenylpyridine ligands that would normally give rise to green emission when complexed with iridium(III), the 2-(thiophen-2-yl)quinoline was responsible for the observed saturated red emission with CIE coordinates of (0.67, 0.33). The poly(dendrimer) had a high photoluminescence quantum yield (PLQY) for a red emissive species at 72 +/- 7%, which was maintained when blended with 4,4'-bis(carbazol-9-yl)biphenyl (CBP) at a concentration of 10 wt % (PLQY = 74 +/- 8%). Simple two-layer devices containing the blend emissive layer and an electron transporting hole blocking layer had a maximum external quantum efficiency of almost 11%.