Synthesis and electroluminescent properties of red emissive iridium(III) complexes with ester-substituted phenylquinoline ligands

Two cyclometalated iridium(III) complexes, (pqcm)2Ir(pic) and (pqca)2Ir(pic) (pqcmH = 2-phenylquinoline-4-carboxylic acid methyl ester, pqcaH = 2-phenylquinoline-4-carboxylic acid adamantanemethyl ester, pic = picolinate), were successfully synthesized and characterized by NMR spectroscopy and mass spectrometry. The photoluminescence spectrum of (pqcm)2Ir(pic) shows emission maximum at 661 nm with a lifetime of 122 ns and quantum yield of ca. 0.028. Replacing the methyl unit with 1-adamantanemethyl unit, the longer lifetime (161 ns) and higher quantum yield (0.040) of (pqca)2Ir(pic) was obtained. Polymer light-emitting devices using these complexes as dopant exhibited intense saturated red emission with CIE coordinates of (0.66,0.29). The devices with 2% doping concentrations of (pqcm)2Ir(pic) have the best performance with a maximum external quantum efficiency of 10.3% and luminance efficiency of 3.97 cd/A. The devices doped (pqca)2Ir(pic) has a higher luminous efficiency (4.17 cd/A) but lower external quantum efficiency (3.65%).