Deep Red Emitting Heteroleptic Ir(III) Complexes that Incorporate Unsymmetrical 4‐quinoline Carboxylic Acid Derived Ligands

Abstract

AbstractSix disubstituted ligands based upon 2‐(2′‐pyridinyl/pyrazinyl)quinoline‐4‐carboxylic acids have been synthesised, solvent‐free, in one step from a range of commercially available isatin derivatives. These species behave as ancillary chelating ligands for Ir(III) complexes of the form [Ir(C^N)2(N^N)]PF6 (where C^N=cyclometalating ligand; N^N=2‐(2′‐pyridinyl/pyrazinyl)quinoline‐4‐carboxylic acids). An X‐ray crystallographic study on one complex shows a distorted octahedral geometry wherein a cis‐C,C and trans‐N,N coordination mode is observed for the cyclometalating ligands. DFT calculations predicted that variations in N^N ligand from 2,2′‐bipyridine to L1–6 should localise the LUMO on to the Ln ligand and that the complexes are predicted to display MLCT/LLCT character. All complexes displayed luminescence in the deep red part of the visible region (674–679 nm) and emit from triplet states, but with little apparent tuning as a function of L1–6. Further time‐resolved transient absorption spectroscopy supports the participation of these triplet states to the excited state character.