The synthesis and properties of iridium cored dendrimers with carbazole dendrons

A convergent procedure has been developed for the preparation of fac-tris(2-phenylpyridyl)iridium(III) cored dendrimers with first- and second-generation dendrons that each contain one and two carbazole units, respectively. The carbazole moieties are both an electroactive moiety and a branching unit in the dendron. The photoluminescence quantum yields of neat films of the first- and second-generation dendrimers were 48 ± 5% and 39 ± 4%, respectively. These values are substantially higher than for equivalent first- and second-generation dendrimers with phenyl moieties at the branching points of the dendrons instead of the carbazole units. The improved solid state luminescent properties can be attributed to the increased steric demand of the carbazole unit relative to the phenyl ring, which reduces more effectively the intermolecular interactions that cause the cores to be less emissive. Electrochemical experiments showed that both the core of the dendrimers and the dendrons were electroactive. Thin film hole mobilities of the first-generation dendrimer with the carbazolyl branching units in the dendrons were found to be higher than the equivalent dendrimer with biphenyl branching units across a range of fields.