Effect of co-ligand number on the optoelectronic properties of first- and second-generation heteroleptic green emissive iridium(iii) complex-cored dendrimers

Abstract

We report the development of light-emitting dendrimers with heteroleptic or homoleptic iridium(III) complexes at the core, with one, two, or three first- or second-generation biphenyl-based dendrons attached to the 2-phenylpyridyl ligand that is involved in the emission of light. The 5-phenyl-1-methyl-3-n-propyl-1H-1,2,4-triazole co-ligand was not dendronised and was not involved in the emission process. The dendrimers with two emissive ligands were found to have the highest solution photoluminescence quantum yields (PLQYs) which were greater than 90% independent of the dendrimer generation. The second-generation dendrimers were all found to have higher neat film PLQYs than their first-generation counterparts due to the increased shielding of the emissive core by the dendrons and surface groups. The maximum external quantum efficiencies of devices made from the neat film and a guest:host blend of the second-generation dendrimer with two emissive ligands were found to be the highest (7.5% and 15.8%, respectively), which was attributed to a balance between the interactions required for charge transport and minimising those that lead to non-radiative processes. Thus, we have demonstrated that combining dendrimer generation and number of emissive dendronised ligands is a viable strategy for optimising light-emitting dendrimer OLED performance.