Deep-blue electroluminescence from nondoped and doped organic light-emitting diodes (OLEDs) based on a new monoazahelicene†
A new organic electroluminescent material, monoazahelicene (1), was successfully prepared via an effective photochemical reaction in about 10 minutes with high productivity. The thermal, photophysical, electrochemical properties, quantum chemical and X-ray structural studies as well as characteristics of organic light-emitting diodes were fully investigated. 1 exhibited excellent solubility and high thermal stability. The first singlet excitation energy of 1 was measured to be around 2.92 eV with a HOMO level of −5.19 eV and a LUMO level of −2.27 eV. Helical molecular geometry of 1 effectively blocked the π-conjugation and decreased the close-packing of molecules. Both the nondoped and doped OLEDs emitted deep-blue light at 444 and 462 nm with CIE coordinates of (0.15, 0.09) and (0.15, 0.10). The doped OLED based on 1 was the first example of helicenes as light emitters that exhibited a brightness of more than 3000 cd m−2 with high color purity and excellent efficiency stability.