Efficient OLEDs with saturated yellow and red emission based on rigid tetradentate Pt(II) complexes

Novel four Pt (II) complexes (1, 2, 3 and 4) supported by rigid tetradentate ligands were prepared as dopants for phosphorescent organic light-emitting diodes (PHOLEDs). These Pt (II) complexes showed similar coordination environment around metal ion except that there was an additional benzene ring fused to the coordination pyridine unit at different positions in 2-4. The extension of pi-conjugated length of the ligands led to the decrease in Delta EHOMO-LUMO of 2 and 4. As a result, a remarkable luminescence red-shift from yellow to red was observed in their emission spectra. Interestingly, saturated yellow and red OLEDs based on these four complexes were fabricated. The yellow OLED device based on 1 at the doping level of 5 wt% achieved a maximum efficiency of 35.0 cd/A and 27.91 m/W, and external quantum efficiency (EQE) of 12.6% with the Commission Internationale de l'Eclairage (CIE) of (0.49, 0.51). An efficient red PHOLED based on 2 was achieved with current efficiency of 12.0 cd/A, power efficiency of 10.71 m/W and EQE of 9.4% with the CIE of (0.64, 0.36). PHOLED based on 3 achieved similar device performance to that of 1 (35.5 cd/A and 29.21 m/W, and EQE of 12.3%) with CIE of (0.47, 0.52). The utilization of 1-arylisoquinoline ligand in 4 led to a deep red emission with the CIE of (0.72, 0.28) and EQE of 2.8%.