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

Abstract

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 (Nd³⁺, Er³⁺, and Yb³⁺). 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 (T_d) and glass transition (T_g) 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 Nd³⁺, 0.46 μW cm⁻² and 0.004% for Er³⁺, and 86 μW cm⁻² and 0.14% for Yb³⁺, respectively.