Tuning iridium(III) complexes containing 2-benzo[ b]thiophen-2-yl-pyridine based ligands in the red region

Abstract

Synthesis and characterization of four iridium(III) complexes containing 2-benzo[ b]thiophen-2-yl-pyridine based ligands are reported. The absorption, emission, electrochemistry, and thermostability of the complexes were systematically investigated. The (btmp) 2Ir(acac) (btmp = 2-benzo[ b]thiophen-2-yl-4-methyl-pyridyl, acac = acetyl acetone) was characterized using X-ray crystallography. Calculation on the electronic ground state for (btmp) 2Ir(acac) was carried out using B3LYP density functional theory, HOMO levels are a mixture of Ir and btmp ligand orbitals, while the LUMO is predominantly btmp ligand based. Introduction of substituents (CH 3, CF 3) into pyridyl ring in a typical red emitter (btp) 2Ir(acac) leads to a marked decrease in the sublimation temperature, which is more suitable for OLEDs process. Electrochemical studies showed that (btmp) 2Ir(acac) has a slightly lower oxidation potential, but (btfmp) 2Ir(acac), (btfmp) 2Ir(dbm), and (btfmp) 2Ir(pic) (btfmp = 2-benzo[ b]thiophen-2-yl-5-trifluoromethyl-pyridine, dbm = dibenzoylmethane, pic = 2-picolinic acid) containing CF 3 group are much difficult to oxidate than (btp) 2Ir(acac). The emission characteristics of these complexes can be tuned by either changing the substituents and their position on 2-benzo[ b]thiophen-2-yl-pyridine or using different monoanionic ligands, showing emission λ max values from 604 to 638 nm in CH 2Cl 2 solution at room temperature.