Blue Phosphorescent Iridium Complexes with Fluorine-free Main Ligands for Efficient Organic Light-emitting Diodes

Two heteroleptic iridium(III) complexes with fluorine-free pyridylpyrimidine main ligands were designed and synthesized for use as blue phosphorescent emitters in organic light-emitting diodes (OLEDs). Complexes 1 and 2 have a molecular formula of Ir(C<^>N)(2)(L<^>X), where C<^>N = 2-tert-butyl-5-(pyridin-2-yl) pyrimidine (b5ppmH) is the main ligand and L<^>X = picolinic acid (pic) and 2-(1H-tetrazol-5-yl) pyridine (ptz) are ancillary ligands. The thermal, photophysical, and electrochemical properties of these complexes were investigated. Even without electron-withdrawing fluorine substituents, the complexes emitted blue light at 463 and 455 nm with moderate quantum efficiencies (Phi(PL) = 0.54 and 0.43), respectively. Furthermore, the replacement of the pyridine ring with a pyrimidine ring allowed blue emission without fluorine substituents. An organic light-emitting device fabricated using complex 2 as a dopant and 1,3-bis(N-carbazolyl) benzene (mCP) as a host exhibited a maximum external quantum efficiency of 11.5% and color coordinates of (0.17, 0.26) at 100 cd/m(2).