A rapid route to carbazole containing dendrons and phosphorescent dendrimers

A convergent strategy for the synthesis of three generations of dendrons comprised of carbazole moieties is described. The procedure to build the dendrons involves an iterative palladium catalysed amination-debenzylation sequence using N-benzyl-3,6-dibromocarbazole. The three carbazolyl focussed dendrons are then attached to a reactive fac-tris[2-phenylpyridyl]iridium(III) core by a palladium catalysed amination to give the dendrimers. The three generations of dendrons have one, three, and seven carbazole units leading to dendrimers with fac-tris[2-phenylpyridyl]iridium(III) cores and three, nine and twenty one carbazole units. The use of 9,9'-dialkylfluorenyl surface groups gave the dendrimers excellent solubility. The attachment of the carbazolyl-based dendrons did not change the emission colour significantly with the dendrimers emitting green phosphorescence. The dendrimers were highly luminescent with solution photoluminescence quantum yields of the order of 70%. Ground state molecular orbital calculations showed that while the 'LUMO' was concentrated on the core iridium(III) complex the 'HOMO' was delocalised across the core and each of the dendrons. This was reflected in the oxidation properties of the dendrimers whereby the increased carbazolyl character of the 'HOMO'resulted in the first oxidation being moved to more positive potentials.