Dual phosphorescence emission of dinuclear platinum(II) complex incorporating cyclometallating pyrenyl-dipyridine-based ligand and its application in near-infrared solution-processed polymer light-emitting diodes

摘要

Two novel mono- and binuclear cyclometalated platinum(II) complexes of (BuPyrDPy) Pt(dpm) and (BuPyrDPy)[Pt(dpm)](2) incorporating a pyrenyl-dipyridine-based cyclometalated ligand were synthesized and characterized, respectively. Single-crystal X-ray diffraction of the two materials revealed each complex's coordination mode; their photophysical, electrochemical as well as electroluminescent properties were also investigated. Both complexes exhibited good solubility and excellent thermal stability. (BuPyrDPy)[Pt(dpm)](2) presented dual phosphorescence emissive character at room-temperature and showed an increased quantum efficiency compared to that of (BuPyrDPy) Pt(dpm). Density functional theory (DFT) calculations were carried out to model their photophysical process, and found a significant contribution of the second Pt center to the LUMO plot, giving the T-1 and T-2 states considerable LMCT nature, which is quite rare in metallic complexes. A device with the structure of ITO/PEDOT (40 nm)/PVK : 30 wt% OXD-7 : 16 wt% (BuPyrDPy)[Pt(dpm)](2) (60 nm)/TPBI (30 nm)/Ba (4 nm)/Al (100 nm) showed a stable NIR emission peak at 695 nm accompanied by two shoulders at 599 nm and 762 nm, with a maximum external quantum efficiency (EQE) of 0.31% and a radiance of 26.9 mW cm(-2), which are about 2 and 1.4 times higher than those of (BuPyrDPy) Pt(dpm)-doped devices. This study provides an efficient strategy to simultaneously design novel biluminescent materials and achieve NIR emission through adjusting the emissive triplet states by introducing a second metal into an asymmetric bimetallic system.