The novel synthesis of tris-cyclometalated iridium(III) complexes for saturated red organic light-emitting diodes with low efficiency roll-off

Abstract

A series of homoleptic tris-cyclometalated iridium(III) complexes (Ir2–Ir4) have been synthesized by the direct functionalization of a template complex (Ir1) through a Suzuki cross-coupling reaction. We revealed the coordination arrangement of Ir4 by single X-ray structural analysis and the molecule showed a facial configuration. All the complexes showed red emission with emission maxima at 591–624 nm, short lifetimes of 1.38–2.19 μs and photoluminescence quantum yields in the range of 28–42%. Most importantly, the full width at half maximum (FWHM) of the emission maxima of these complexes was less than 48 nm. These complexes exhibited good thermal stability with Td of 368–400 °C. Density functional theory (DFT) calculations were used to study the electronic structure information of these iridium(III) complexes. Organic light emitting diodes (OLEDs) based on these complexes as dopant emissive materials were fabricated. Among them the device based on Ir1 has a maximum current efficiency and external quantum efficiency of 15.67 cd A−1 and 10.06%, respectively. The device with low efficiency and EQE roll-off that 97–99% efficiency and EQEmax maintained at 1000 cd m−2. Meanwhile, the CIE(x,y) coordinates of these extended complexes were (0.65, 0.33), (0.66, 0.33) and (0.68, 0.31), respectively. These data were very close to the standard red emission required by National Television System Committee (NTSC) (0.67, 0.33). These results suggest that these materials have potential application in OLEDs.