Phosphorescent, green-emitting Ir(III) complexes with carbazolyl-substituted 2-phenylpyridine ligands: Effect of binding mode of the carbazole group on photoluminescence and electrophosphorescence

The ligands, 9-((6-phenylpyridin-3-yl)methyl)-9H-carbazole and 9-(4-(pyridin-2-yl)benzyl)-9H-carbazole were synthesized by attaching a carbazolyl group to the pyridine and phenyl rings of 2-phenylpyridine, respectively. Ir(III) complexes were prepared by a simple procedure and the solubility of the novel complexes was significantly better than that of the conventional, green-emitting conventional fac-tris(2-phenylpyridinato-C2,N)iridium(III). The Ir(III) complexes were used to prepare electrophosphorescent polymer light-emitting devices. The device comprising 10% of fac-tris(2-(4′-((9H-carbazol-9-yl)methyl)phenyl)pyridinato-C2,N)iridium(III) exhibited an external quantum efficiency of 7.88%, luminous efficiency of 23.01 cd/A, and maximum brightness of 32,640 cd/m2. The color of the emissions of fac-tris(2-(4′-((9H-carbazol-9-yl)methyl)phenyl)pyridinato-C2,N)iridium(III) was similar to that of conventional fac-tris(2-phenylpyridinato-C2,N)iridium(III). This work shows that integration of a rigid hole-transporting carbazole and phosphorescent complex in one molecule provides a new route to highly efficient, solution-processable complexes for electrophosphorescent applications.