Electrophosphorescent Chelating Copolymers Based on Linkage Isomers of Naphthylpyridine−Iridium Complexes with Fluorene

Abstract

A series of phosphorescent chelating copolymers based on the linkage isomers of 2-(1-naphthalene)pyridine− and 2-(2-naphthalene)pyridine−bicycloiridium complexes were synthesized by Suzuki polycondensation of A−A- and B−B-type monomers. These linkage isomers-based copolymers show distinct differences in their photophysical and electroluminescence properties. The phosphorescent emission band of the copolymer PF1−NpyIrm is in the region of 630 nm, whereas copolymers PF2−NpyIrm show an emission with the peak maximum at 590 nm, which are both red-shifted around 20 nm compared with the emissions of the pristine complexes. The highly efficient saturated red-phosphorescent PLEDs were achieved on the basis of copolymers PF1−NpyIrm. The best device performances are observed from copolymer PF1−NpyIrm1 with an external quantum efficiency (ηext) of 6.5% photon/electron (ph/el) at the current density of 38 mA/cm2, with the emission peak at 630 nm (x = 0.65, y = 0.31) and the luminance of 926 cd/m2. The efficiency remains as high as ηext = 5.3% ph/el at a high current density of 100 mA/cm2. No remarkable efficiency decay with the increase in current density shows that the chelating copolymers are promising candidate materials for phosphorescent polymer light-emitting diodes (PHPLEDs).