Bis-ZnII salphen complexes bearing pyridyl functionalized ligands for efficient organic light-emitting diodes (OLEDs)
Inspired by the emissive features of ZnII complexes based on bis-Schiff base ligands, bis-ZnII salphen complexes bearing pyridyl functionalized ligands have been successfully synthesized. Their photophysical features, electrochemical behavior and electroluminescent (EL) properties have been investigated in detail. The functionalized bis-ZnII salphen complexes can exhibit high thermal stability up to 417 °C, and their photoluminescence (PL) spectra show a maximal emission wavelength peak at ca. 565 nm both in solution and PMMA doped films. The PL investigation of the neat films for these functionalized bis-ZnII salphen complexes indicated that the pyridyl functionalized ligands can effectively reduce the degree of molecular aggregation to enhance their emission intensity. Taking advantage of the charge carrier injection/transporting ability of the pyridyl functionalized ligands and their dendritic design, the optimized EL devices fabricated by a simple solution-processing method can achieve a peak luminance (Lmax) of 3589 cd m−2, a maximal external quantum efficiency (ηext) of 1.46%, a maximal current efficiency (ηL) of 4.1 cd A−1 and a maximal power efficiency (ηp) of 3.8 lm W−1. These results should afford important instructions for exploiting high performance fluorescent emitters based on dinuclear ZnII complexes.