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

Abstract

A series of symmetric tetradentate platinum (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 Td 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 have narrow full width at half maximum of 38-45 nm in thin films. The phosphorescence spectra of Pt-DPM, Pt-PIP and Pt-DPT showed orange emission peak at 585 nm, 588nm and 580nm in PMMA film at a concentration of 1 wt % at room temperature. Furthermore, introduction of aza-triptycene skeleton with rigid steric hindrance reduced bimolecular interactions, then lead to a significant increase in the PLQYs (>88%) compared with the reference platinum (II) complex Pt-D. Solution-processed organic light-emitting diodes using three new platinum (II) complexes as emitters show excellent performance. The device based on the reference platinum complex Pt-D shows a peak external quantum efficiency, current efficiency, and brightness of 4.35 %, 1.97 cd A-1, and 16926 cd m-2, respectively. The efficiencies are dramatically improved to 9.67%, 23.67 cd A-1, and 26670 cd m-2 for the OLED based on the sterically hindered aza-triptycene tetradentate platinum (II) complex Pt-DPM with methyl substituted, and to 16.94%, 44.66 cd A-1, and 54918 cd m-2 for the OLED based on the sterically hindered aza-triptycene tetradentate platinum (II) complex Pt-DPT with isopropyl group substituted, respectively. Due to the introduction of aza-triptycene unit and isopropyl group with steric hindrance, the device has good properties even at high doping concentration. When neat device based on Pt-DPT was adopted as the emitting layer, the non-doped orange device gives a high-brightness of 10873 cd m-2 and 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 application in OLEDs.