Concentration-dependent circularly polarized luminescence of chiral cyclometalated platinum(II) complexes for electroluminescence

Circularly polarized organic light-emitting diodes (CP-OLEDs) have been attracting increasing attention due to the direct generation of CP light, and they show the improved image contrast and luminous efficiency in OLEDs displays. In this work, a pair of chiral Pt(II) complexes with methylbenzylisocyanide and 1,3-bis(2-pyridyl)benzene as a tridentate N^∧C^∧N ligand were synthesized. Both of them exhibited bright green emission in dilute acetonitrile solution, while strong orange emission in high concentration of acetonitrile solution. However, when the complexes were doped into polymethyl methacrylate, the green emission originated from intrinsic single molecule can be changed to the red emission from excimer by adjusting the doping ratios. More importantly, the amplification of CPL signal can be achieved compared with the solution state. Furthermore, the monochrome devices were fabricated by utilizing these two enantiomers as emitters.