Cationic Iridium(III) Complexes with Benzothiophene-Quinoline Ligands for Deep-Red Light-Emitting Electrochemical Cells.

Three new cationic cyclometalated iridium(III) complexes equipped with differently substituted benzo[ b ]thiophen-2-ylquinoline cyclometalating ligands and with a sterically demanding tert -butyl-substituted 2,2'-bipyridine ancillary ligand were synthesized and structurally characterized by NMR and X-ray diffraction techniques. To tune the electronic properties of such complexes, the quinoline moiety of the cyclometalating ligands was kept pristine or equipped with electron-withdrawing phenyl and -CF 3 substituents, leading to complexes 1 , 2 , and 3 , respectively. A complete electrochemical and photophysical investigation, supported by density functional theory calculations, permits a deep understanding of their electronic properties. The emission of all complexes arises from ligand-centered triplet states in the spectral range between 625 and 950 nm, with excited-state lifetimes between 2.10 and 6.32 μs at 298 K. The unsubstituted complex ( 1 ) exhibits the most blue-shifted emission in polymeric matrix at 298 K (λ max = 667 nm, photoluminescence quantum yield (PLQY) = 0.25 and τ = 5.32 μs). The phenyl-substituted complex ( 2 ) displays the highest photoluminescent quantum yields (up to 0.30 in polymeric matrix), while the CF 3 -substituted counterpart ( 3 ) shows the most red-shifted emission, peaking at approx. 720 nm, but with lower quantum yields ( e.g. , 0.10 in polymeric matrix at 298 K). Complexes 1 and 2 were tested in single-layer nondoped light-emitting electrochemical cells (LEECs), using a nozzle-printing technique; both devices display deep-red electroluminescence with an external quantum efficiency close to 20%.