π-conjugated chelating polymers with charged iridium complexes in the backbones: Synthesis, characterization, energy transfer, and electrochemical properties

A series of π-conjugated chelating polymers with charged iridium (Ir) complexes in the backbones were synthesized by a Suzuki polycondensation reaction, leading to homogeneous polymeric materials that phosphoresce red light. The fluorene and bipyridine (bpy) segments were used as polymer backbones. 5.5′-Dibromobipyridine served as a ligand to form a charged iridium complex monomer with 1-(9′9-dioctylfluorene-2-yl)isoquinoline (Fiq) as the cyclometalated ligand. Chemical and photophysical characterization confirmed that Ir complexes were incorporated into the backbones as one of the repeat units by means of the 5.5′-dibromobipyridine ligand. Chelating polymers showed almost complete energy transfer from the host fluorene segments to the guest Ir complexes in the solid state when the feed ratio was 2 mol%. In the films of the corresponding blend system, however, energy transfer was not complete even when the content of Ir complexes was as high as 16 mol%. Both intra- and in termolecular energy-transfer processes existed in this host-guest system, and the intramolecular energy transfer was a more efficient process. All chelating polymers displayed good thermal stability, redox reversibility, and film formation. These chelating polymers also showed more efficient energy transfer than the corresponding blended system and the mechanism of incorporation of the charged Ir complexes into the π-conjugated polymer backbones efficiently avoided the intrinsic problems associated with the blend system, thus offering promise in optoelectronic applications.