Efficient saturated red light-emitting polyfluorenes containing iridium complexes in side chains

Abstract

A series of electrophosphorescent copolymers were synthesized by Suzuki polymerization. A diketone-ended alkyl chain which is grafted in the N-position of the carbazole unit is used as a ligand to form a pendant cyclometalated Ir complex with 1-(9,9-dioctyl-9H-fluoren-2-yl)isoquinoline and 1-(N,N-diphenyl-benzenamine-4-yl)isoquinoline. The electroluminescence from the backbone of the copolymers is completely quenched by tethered iridium complexes even though with the content of iridium complexes being as low as 1 mol%. Saturated red light-emitting diodes were fabricated on the basis of these two series of copolymers. The best device performance with a maximum external quantum efficiency of 7.8% on the basis of copolymer PF-IrNiq1 was achieved, which was among the highest efficiencies of the reported electrophosphorescent red light-emitting polymers comprising iridium ligands.