Efficient Phosphorescence by Reducing lntrachain Chromophore Interactions in Dendrimer-Containing Polymers

Poly(dendrimers) comprised of a poly(styrene) backbone with dendrimer side chains containing an iridium(III) complex core, first-generation biphenyl dendrons, and (2-ethylhexyl)oxy surface groups show increased viscosity compared to their individual dendrimer components, which is important for inkjet printing processes. However, intrachain interchromophore interactions lead to lower photoluminescence quantum yields even in solution relative to the simple isolated dendrimers. We demonstrate that the phosphorescence efficiency of a polymer can be enhanced by incorporating the dendrirner monomer unit(s) into a copolymer with poly(styrene) spacer units. The poly(styrene) spacer units remove the intrachain interchromophore interactions between the chromophores in solution. The copolymer gives a >50% increase in solution photoluminescence quantum yields (to 94%) and an improved organic light-emitting diode performance with an external quantum efficiency of 6.7% at 100 cd/m(2) at 11 V when compared to the homopolymer with the same dendrimer side chain.