The synthesis and properties of carbazole-phenylazomethine double layer-type dendrimers

A new double layer-type dendrimer with carbazole as the outer layer and phenylazomethine as the inner layer of the dendron was synthesized using the Ullmann reaction and dehydration reaction in the presence of titanium tetrachloride. In this dendrimer, the carbazole units act as excellent hole-transporters, the phenylazomethine units act as metal assembling sites, and the combination of both units provides a thermally stable shell for which the 10% weight loss temperature was over 550°C. The dendrimers were used as the hole-transporting layer in an OLED device. The OLED device performance increased when the generation of the carbazole increased, corresponding to the higher HOMO level. Additionally, the enhancement of the hole-transporting property was observed by simple complexation of the metal ions to the imine site. Next, the effect of the generation of phenylazomethine was observed and compared to the asymmetric-type carbazole-phenylazomethine dendrimers. When the generation of phenylazomethine increased in the asymmetric-type dendrimer, the device performance decreased. In contrast, the performance did not change using the double layer-type dendrimer. This indicates that the outer layer carbazole works as a hole-transporting shell, and the double layer-type architecture is an ideal structure.