Synthesis and optoelectronic characterization of conjugated phosphorescent polyelectrolytes with a neutral Ir complex incorporated into the polymer backbone and their neutral precursors

Abstract

A series of conjugated polyelectrolytes and their neutral precursor with a neutral Ir complex incorporated into an aminoalkyl-substituted polyfluorene backbone with ionic groups (amino or quaternized ammonium groups) in the polymer side chain were synthesized by Suzuki polycondensation. The phosphorescent devices from polyelectrolytes and their neutral precursors emit orange–red light in the region of 598–602 nm, around 70 nm red-shifted in comparison with a pristine Ir(ppy)₃ complex. The resultant polyelectrolytes and their neutral precursors can be easily dissolved and processed from environmentally-friendly solvents such as alcohols. The efficient orange-phosphorescent polymeric light-emitting diodes (PLEDs) were achieved with a high work-function metal, such as Al or Au, as the cathode. The best device performances are observed from neutral precursor PFN-DppyIrppy5 with an external quantum efficiency (EQE) of 0.69% and 0.54% and luminance efficiency (LE) of 1.42 cd A^–1 and 1.10 cd A^–1 for Al and Au as the cathode, respectively. These copolymers can also be used as the injection layer span on top of varieties of EL polymers as emitting layers with Al or Au as the cathode. For example, with PFN-DppyIrppy10 as the injection layer and P-PPV as the emissive layer, the device achieves an EQE of 1.67% with LE of 4.2 cd A^–1 with Au as the cathode, compared with the P-PPV device performance of only 0.003% and 0.008 cd A^–1 with Au as cathode.