Bis-Zn^II salphen complexes bearing pyridyl functionalized ligands for efficient organic light-emitting diodes (OLEDs)

Inspired by the emissive features of Zn^II complexes based on bis-Schiff base ligands, bis-Zn^II 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-Zn^II 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-Zn^II 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 (L_max) of 3589 cd m^-2, a maximal external quantum efficiency (η_ext) of 1.46%, a maximal current efficiency (η_L) of 4.1 cd A^-1 and a maximal power efficiency (η_p) of 3.8 lm W^-1. These results should afford important instructions for exploiting high performance fluorescent emitters based on dinuclear Zn^II complexes.