Cooperative structural modulation on main ligand and ancillary ligand in iridium(III) complexes to achieve high-performance OLEDs

Abstract

Three new cyclometalated iridium(III) complexes (Ir1-Ir3) based on trifluoromethyl substituted phenylpyrazole (CF₃-ppz and 2CF₃-ppz) as main ligands and picolinic acid (Hpic)/potassium tetraphenylimidodiphosphinate (Ktpip) as ancillary ligands have been synthesized and fully characterized by NMR, mass spectrometry and X-ray crystallography. With the aid of experimental and theoretical methods, the important roles of -CF₃ group on main ligands and different ancillary ligands on the photophysical and electrochemical properties were investigated systematically. All complexes displayed green emission peaks at 512–528 nm with photoluminescence quantum yields (PLQYs) of 13.1–19.9 % and photoluminescence lifetimes (τ) of 0.57–0.86 µs in degassed CH₂Cl₂ at room temperature. The resulting organic light-emitting diode (OLED) devices (D1-D3) with these complexes as emitters have been fabricated, and achieved green to yellow-green electroluminescence with the maximum external quantum efficiency (EQE_max) of 2.5–8.5 % and maximum luminance (L_max) of 1687–3519 cd m⁻². As a result, complex Ir3 and device D3 show the best photoluminescence (PL) and electroluminescence (EL) properties, respectively. Therefore, designing Ir(III) complexes by introducing more -CF₃ groups on main ligands and changing as electronically portable tpip ancillary ligand provides an effective strategy for exploring high-performance OLEDs.