Coordination polymers based on bis-Zn^II salphen complexes and functional ditopic ligands for efficient polymer light-emitting diodes (PLEDs)

Encouraged by the high photoluminescence (PL) of the bis-Zn^II salphen complexes, a series of coordination polymers have been successfully developed through metal-ligand interactions between the bis-Zn^II salphen complexes and functional ditopic ligands. These bis-Zn^II salphen coordination polymers can exhibit high thermal stability up to 433 °C. Their PL spectra show an emission maximum peaking at ca. 570 nm in solution and ca. 580 nm in neat films. The PL investigation of the neat films for these bis-Zn^II salphen coordination polymers has indicated that the functional ditopic ligands can restrain the molecular packing among the bis-Zn^II salphen units for enhancing their PL intensity. Hence, the functional ditopic ligands should exhibit great potential in avoiding exciton quenching in the emission layer formed by these bis-Zn^II salphen coordination polymers in polymer light-emitting diodes (PLEDs). Benefiting from such a molecular design, these bis-Zn^II salphen coordination polymers can exhibit a peak luminance (L_max) of 8658 cd m^-2, a maximum external quantum efficiency (η_ext) of 3.18%, a maximum current efficiency (η_L) of 6.2 cd A^-1 and a maximum power efficiency (η_P) of 4.4 lm W^-1. These attractive results represent the state-of-the-art EL performances ever achieved by Schiff base Zn^II coordination polymers, which would provide significant clues for developing high performance PLEDs based on Schiff base Zn^II coordination polymers.