Highly efficient orange OLEDs with narrow-emitting symmetric tetradentate platinum(ii) complexes based on rigid steric hindrance aza-triptycene pyridazine ligands

Abstract

A series of symmetric tetradentate Pt(II) complexes with rigid steric hinderance aza-triptycene pyridazine ligands Pt-DPM, Pt-PIP and Pt-DPT were synthesized and fully characterized. These complexes exhibited excellent thermal stability with T_d values of 407–462 °C. All these complexes showed orange emission with emission maxima at 580–593 nm and short lifetimes of 3.37–3.82 μs. Most importantly, these complexes exhibit narrow full widths at half maximum of 38–45 nm in thin films. Furthermore, the introduction of an aza-triptycene skeleton with a Y-shaped rigid 3D molecular structure reduced bimolecular interactions, leading to a significant increase in the PLQYs (>88%) compared with the reference Pt(II) complex Pt-D. Solution-processed organic light-emitting diodes using three new Pt(II) complexes as emitters show excellent performance. The efficiencies are dramatically improved to 9.67%, 23.67 cd A⁻¹, and 26 670 cd m⁻² for the OLED based on Pt-DPM, and to 16.94%, 44.66 cd A⁻¹, and 54 918 cd m⁻² for that based on Pt-DPT, respectively. Due to the introduction of an aza-triptycene unit and isopropyl group with steric hindrance, the device exhibits good properties even at high doping concentrations. When a neat device based on Pt-DPT was adopted as the emitting layer, the non-doped orange device exhibited a high brightness of 10 873 cd m⁻² and a luminous efficiency of 9.56 cd A⁻¹ along with CIE coordinates of (0.59, 0.40). These results suggest that these materials have potential applications in OLEDs.