Fluoro-benzenesulfonyl-functionalized 2-phenylthiazole-type iridium(iii) complexes for efficient solution-processed organic light-emitting diodes

Abstract

The thiazole unit can exhibit both electron-deficient and electron-rich features, which provides more possibilities for shaping the photophysical and electroluminescence (EL) properties of the Ir(III) complex emitters. Herein, a series of cyclometalated Ir(III) complexes were synthesized from the 2-phenylthiazole-type ligands bearing fluorinated benzenesulfonyl moieties. Their thermal stabilities, photophysical and electrochemical properties and EL performances were fully studied. They can emit intense orange phosphorescence with peaks ranging from 577 to 590 nm, and the phosphorescence quantum yield (Φ_p) can be up to 0.89. Interestingly, when the number of fluorine atoms on the phenyl ring of the benzenesulfonyl moiety increases, their absorption and emission maxima both show red-shift effects, which were interpreted by the related theoretical calculation results. Besides, their LUMO levels follow a decreasing trend as the fluorine atoms increase, leading to good electron injection/transporting (EI/ET) properties. Finally, their EL performances were characterized by their solution processed OLEDs, which achieve the best EL efficiencies with a maximal current efficiency (η_L) of 27.5 cd A⁻¹, a maximal power efficiency (η_p) of 17.3 lm W⁻¹ and a maximal external quantum efficiency (η_ext) of 12.3%, these results can outcompete the EL efficiencies of the reported solution processed OLEDs built by the thiazole-based Ir(III) complexes. All the concerned results should offer inspirations for Ir(III) complex functionalizations and reveal the great potential of 2-phenylthiazole ligands with fluoro-benzenesulfonyl moieties in developing high performance emitters.