The Investigation of Triazolophenanthridine Based NHC-Iridium Complexes: Synthesis, Photophysics and PHOLED Applications
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Ir(Phenyl), Ir(Tolyl), and Ir(Xylenyl) were isolated, and investigation of their photophysical properties was carried out. The crystal structures of Ir complexes were determined, and it was found that the meridional isomer of Ir(Phenyl) was not formed but hetero-Ir(Phenyl) was formed. In the case of homoleptic complexes, orbitals are located in the metal and phenyl part of phenanthridine in HOMO, and in the entire phenanthridine in LUMO. Hetero-Ir(Phenyl) has orbital distribution extended to the phenyl moiety, where the HOMO is located in the metal and phenyl moiety, and LUMO is located in the phenanthridine. The energy of hetero-Ir(Phenyl) was stabilized and red-shifted emission. Ir complexes were applied to PHOLED and the fabricated device exhibited efficient blue emission. Hetero-Ir(Phenyl) showed relatively higher efficiency with an external quantum efficiency (EQE) of up to 16.2%. Similar to the properties in the solvent, the facial isomer was closer to the deep-blue emission.