Substituent effects of iridium complexes for highly efficient red OLEDs

This study reports substituent effects of iridium complexes with 1-phenylisoquinoline ligands. The emission spectra and phosphorescence quantum yields of the complexes differ from that of tris(1-phenylisoquinolinato-C2,N)iridium(III) (Irpiq) depending on the substituents. The maximum emission peak, quantum yield and lifetime of those complexes ranged from 598–635 nm, 0.17–0.32 and 1.07–2.34 µs, respectively. This indicates the nature of the substituents has a significant influence on the kinetics of the excited-state decay. The substituents attached to phenyl ring have an influence on a stability of the HOMO. Furthermore, those substituents have effect on the contribution to a mixing between 3π–π* and 3MLCT for the lowest excited states. Some of the complexes display the larger quantum yield than Irpiq, which has the quantum yield of 0.22. The organic light emitting diode (OLED) device based on tris [1-(4-fluoro-5-methylphenyl)isoquinolinato-C2,N]iridium(III) (Ir4F5Mpiq) yielded high external quantum efficiency of 15.5% and a power efficiency of 12.4 lm W−1 at a luminance of 218 cd m−2. An emission color of the device was close to an NTSC specification with CIE chromaticity characteristics of (0.66, 0.34).