First Iridium Complex End-Capped Polyfluorene: Improving Device Performance for Phosphorescent Polymer Light-Emitting Diodes

Two types of fluorene-based copolymers, with 1-phenylisoquinoline-iridium complexes incorporated into the polyfluorene main chain by either embedding (P1 and P2) or end-capping (P3) manners via ancillary ligand β-diketonate were synthesized by the Suzuki polycondensation reaction and characterized by 1H NMR, 13C NMR, elemental analysis, and GPC. The electrochemical investigation reveals that the HOMO and LUMO energy levels of the monomeric iridium complexes fall within those of the parent polyfluorene, implying that the iridium complexes in the polymers could function as traps for both electrons and holes under electrical excitation. The different connection manners between the iridium complex and polyfluorene backbone have a significant effect on their photophysical and electroluminescent properties. The absorption spectra of P1−P3 are mostly characteristic of the polyfluorene backbone. The PL spectra of P1 and P2 are dominated by emission from the iridium complex at 625 nm, whereas for P3 the emission a...