Constructing lanthanide [Nd(iii), Er(iii) and Yb(iii)] complexes using a tridentate N,N,O-ligand for near-infrared organic light-emitting diodes

A novel type of NIR-emitting lanthanide complexes Ln(PND)3 (Ln = Nd, Er and Yb) was designed and synthesized based on a tridentate monoanionic N,N,O-ligand 6-(pyridin-2-yl)-1,5-naphthyridin-4-ol (PND). Such complex owns definite charge-neutral, coordination-saturated and mononuclear structure that is proved by X-ray single crystal diffraction of Nd(PND)3. Photophysical studies on the ligand and complexes reveal that the PND ligand has suitable energy level to sensitize the near-infrared (NIR) emitting lanthanide ions (Nd(3+), Er(3+), and Yb(3+)). Among the three compounds, Yb(PND)3 shows the highest photoluminescence quantum yield up to 0.9% in a mixture of acetonitrile and methanol solution (10 : 1, v/v, 10(-4) M). Thermal measurements indicate that these compounds have high decomposition (Td) and glass transition (Tg) temperature up to 420 and 265 °C, respectively, implying great advantage for constructing organic electronic devices via vacuum deposition method. At last, NIR organic light-emitting diodes (OLEDs) with simple three-layer structure were fabricated to test their electroluminescent performance, showing maximum NIR irradiance and maximum external quantum efficiency (EQE) of 25 μW cm(-2) and 0.019% for Nd(3+), 0.46 μW cm(-2) and 0.004% for Er(3+), and 86 μW cm(-2) and 0.14% for Yb(3+), respectively.