Effects of Symmetry of Ir (III) Complex on the Photophysical Properties and Device Performances

The optical, electrochemical properties of two isomers of Ir(mpp)2acac (mpp = anion of 3-methyl-2-phenyl-pyridine and acac = acetylacetonate) and the device performance of polymer light emitting devices using two isomers as a triplet emitter have been studied. The two isomers show the symmetric and asymmetric coordination of two mpp ligands to Ir(III), which is confirmed from the 1H NMR spectra. The ligand based absorption is red shifted by 35 nm in asymmetric Ir(mpp)2acac compared to the symmetric Ir(mpp)2acac. The MLCT absorption peak positions are similar in both cases, but the extinction coefficients of the asymmetric Ir(mpp)2acac are higher than those of symmetric Ir(mpp)2acac. The two isomers exhibit similar PL emission spectra but PL lifetimes of two isomers are different. The lifetime of the symmetric Ir(mpp)2acac is 1.74 μs, whereas that of the asymmetric Ir(mpp)2acac is 0.9 μs. The asymmetric Ir(mpp)2acac shows higher electrochemical oxidation potential than that of the symmetric Ir(mpp)2acac. T...