Synthesis and Photophysical, Electrochemical, and Electrophosphorescent Properties of a Series of Iridium(III) Complexes Based on Quinoline Derivatives and Different β-Diketonate Ligands

The synthesis and photophysical, electrochemical, and electrophosphorescent properties of a series of
cyclometalated iridium(III) complexes based on quinoline derivatives (C∧N) and different β-diketonate
ligands are reported. The iridium complexes contain two quinoline derivatives (C∧N) and a single
monoanionic β-diketone (LX), i.e., Ir(C∧N)2(LX), where LX denotes acetylacetonate (acac) or 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolonate (PMIP). Most of the iridium complexes in solution show
phosphorescent emission with high quantum efficiencies (0.05−0.25) and microsecond lifetimes (0.5−1.67 μs). The intense phosphorescent emission of these complexes is the result of significant spin−orbit
coupling of the iridium center. By modification of the chemical structures of quinoline derivative ligands,
the emissive wavelengths of complexes can be tuned from 596 to 634 nm. Interestingly, the
photoluminescence quantum efficiency can be improved by the replacement of acac with PMIP. Energy
transfer from the hosts poly(9,9-dioctylfluorene) (PFO) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) to the guest iridium complex was investigated. Moreover, three iridium complexes
were used as dopants to fabricate electrophosphorescent polymer-based light-emitting diodes (PLEDs).
The PLEDs show red emission with high external quantum efficiencies, ranging from 7.0 to 9.6%.