π-Conjugated Chelating Polymers with a Charged Iridium Complex in the Backbones: Toward Saturated-Red Phosphorescent Polymer Light-Emitting Diodes

A series of π-conjugated chelating polymers with charged iridium (Ir) complex units based on 1,10-phenanthroline in the backbones were synthesized by Suzuki polycondensation, and homogeneous polymeric phosphorescent materials were obtained. 3,8-Dibromo-1,10-phenanthroline served as an N ∧ N ligand to form a charged Ir complex monomer with 1-(9,9-dioctylfluorene-2-yl)isoquinoline (Fiq) as the cyclometalated ligands. Chemical and photophysical characterization confirmed that the Ir complex was incorporated into the backbones as one of the repeat units. Chelating polymers showed efficient energy transfer from the host to the guest in the solid state, and almost complete energy transfer was realized when the feed ratio of the Ir complex monomer was 4 mol %. All chelating polymers displayed good thermal stability, redox reversibility, and film-forming properties. Polymer light-emitting diodes using chelating polymer without carbazole units (phen-PFOIr2) and chelating polymer with carbazole units (phen-PFOCzIr2) as the light-emitting layers were fabricated, and saturated-red electrophosphorescence was achieved.