Poly(dendrimers) with Phosphorescent Iridium(III) Complex-Based Side Chains Prepared via Ring-Opening Metathesis Polymerization

Phosphorescent poly(dendrimers) with a norbornene-derived backbone have been synthesized using ring-opening metathesis polymerization with the Grubbs III catalyst. The dendrimers are comprised of a heteroleptic iridium(III) complex core with two 2-phenylpyridyl ligands and a phenyltriazolyl ligand, biphenyl-based dendrons, and 2-ethylhexyloxy surface groups. The phenyltriazolyl ligand provides the attachment point to the polymer backbone, and the two poly(dendrimers) differ in the number of dendrons attached to the 2-phenylpyridyl ligands. The poly(dendrimer) with one and two dendrons per ligand are termed mono- and doubly dendronized. The mono- and doubly dendronized poly(dendrimers) were found to have relatively narrow polydispersities, around 1.4, viscosities approaching those required for inkjet printing, and could be solution processed to form thin films. The dendrons played an important role in controlling the photophysical properties of the materials. The parent homopolymer with the same iridium(III) complex but no dendrons attached to the ligands had a solution photoluminescence quantum yield (PLQY) of 48%. The solution PLQY was found to increase with increasing number of dendrons with the mono- and doubly dendronized materials having solution PLQYs of 65% and 71%, respectively. The increase in PLQY is due to decreased intrachain interchromophore interactions. A similar trend was observed in the solid state with the parent, mono-, and doubly dendronized polymers having film PLQYs of 2%, 44%, and 58%, respectively, demonstrating that both intra- and interchain interactions are controlled by the dendrons.