Luminescent bis-tridentate iridium(III) complexes: Overcoming the undesirable reactivity of trans-disposed metallated rings using -N∧N∧N--coordinating bis(1,2,4-triazolyl)pyridine ligands

Nine new iridium(III) complexes featuring two tridentate ligands have been synthesised of the form Ir((NCN)-C-boolean AND-N-boolean AND) ((-NNN-)-N-boolean AND-N-boolean AND), where (NCN)-C-boolean AND-N-boolean AND represents a cyclometallating ligand based on 1,3-di(2-pyridyl)benzene and (-NNN-)-N-boolean AND-N-boolean AND is a doubly deprotonated bis(1,2,4-triazolyl)pyridine. Three examples of each ligand have been used, with different substituents in the central aryl ring of the former and para-substituted aryl groups in the 5-positions of the triazole rings of the latter. Two of the complexes have been structurally characterised in the solid-state by X-ray diffraction, confirming the mutually orthogonal arrangement of the two ligands. Unlike related triscyclometallated complexes of the type Ir((NCN)-C-boolean AND-N-boolean AND)((CNC)-N-boolean AND-C-boolean AND), which are unstable with respect to photoactivated cleavage of the trans-disposed Ir-C bonds, the new complexes show no evidence of instability. They are phosphorescent in the green region of the spectrum with lifetimes around 200 ns and quantum yields up to 3%, apparently limited by non-radiative decay processes in particular. Although there is some variation in performance with substitution pattern, the only discernible trend is that complexes of the 4-methoxy-substituted (NCN)-C-boolean AND-N-boolean AND ligand are the better emitters. Three examples of related complexes of the form Ir((NCN)-C-boolean AND-N-boolean AND)((NN-)-N-boolean AND)Cl - incorporating a bidentate 1,2,4-triazolylpyridine - have also been prepared. They show no room-temperature emission but the properties at 77 K are similar to those of the bis-tridentate systems.