Synthesis and properties of phosphorescent iridium(iii) complexes of delocalized ligands

Abstract

New Ir(III) complexes involving N,C-chelating difluorophenyl-pyridine (dfppy) or dibenzo[a,c]phenazine (dbpz) ligands along with either N,N-bound 5-ethynyl-2,2′-bipyridine (e-bpy) or CO + Cl co-ligands have been obtained as [Ir(dfppy)₂(e-bpy)]PF₆, [Ir(dbpz)₂(e-bpy)]PF₆ and cis-[Ir(dbpz)₂(Cl)(CO)]. A single-crystal X-ray diffraction study of cis-[Ir(dbpz)₂(CO)Cl] has shown the Ir(III) centre to adopt a distorted octahedral coordination geometry with cis-CO/Cl and trans-N,N configurations. Pronounced π–π stacking interactions involving different dibenzo[a,c]phenazine units are evident. Electronic absorption and luminescence spectroscopy at 298 K and 77 K, along with cyclic voltammetry were used to study the three complexes. Excited state lifetimes varied from 1.4 to 2.9 μs at rt with quantum yields ranging from 10.2 to 0.7%. With 5-ethynyl-2,2′-bipyridine in the first coordination sphere, the lowest emitting state is that associated with the MLCT band, whereas in the bis-phenazine case the emission is ligand-centred. Importantly, the emission wavelength can be tuned from 552 to 640 nm by changing the conjugation length of the N,C ligand.