Iridium complexes containing p-phenylene units. The influence of the conjugation on the excited state properties

Abstract

The synthesis, characterisation and photophysical properties of a series of heteroleptic iridium complexes are reported. The complexes contain two orthometalating ligands, 2-(2,4-difluorophenyl)pyridine and a bipyridine derivative as the third chelating unit, substituted by 1–3 oligo(para-phenylene) units. We also describe a dinuclear complex in which the two iridium units are connected by a tetra-p-phenylene bridging ligand. All the complexes are strongly luminescent at room temperature and, interestingly, for the longest complexes, the deaerated solution shows an excited state lifetime of several microseconds. The presence of dioxygen reduces the lifetime, dramatically suggesting their potential use as oxygen sensors. At low temperature the emission predominantly originates from the triplet excited state of the ligand involving the poly(phenylene) units and the phosphorescence lifetime increases to several hundreds of microseconds.