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

Abstract

Six 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.

Synthesis and luminescent properties of hetero-bimetallic and hetero-trimetallic Ru(ii)/Au(i) or Ir(iii)/Au(i) complexes

“…The bond lengths and bond angles that describe the distorted octahedral coordination sphere are closely comparable with little variance induced by the addition of cationic imidazolium units (crystal structure metrics can be found in the ESI Tables S1–S3†). In fact, these structural parameters are very closely comparable to previous relevant examples, 23 including those based upon this type of 2-phenylquinoxaline cyclometalating ligand at Ir( iii ). 24…”

“…Single crystals suitable for X-ray crystallographic studies were obtained for the [Ir(Me 3 quinox) 2 (MeCN) 2 ]BF 4 precursor and [Ir Scheme 1 Structures of the N-methyl imidazolium functionalised monometallic Ru(II) and Ir(III) complexes (black) synthesised in this study, together with relevant reference compounds (grey). relevant examples, 23 including those based upon this type of 2-phenylquinoxaline cyclometalating ligand at Ir(III). 24 Reactions with AuCl(PPh 3 ): synthesis and characterisation of the heterometallic complexes (structures shown in Scheme 2).…”

Synthetic ease and exceptional in vivo performance of pyrazole-based cyclometallated iridium complexes

“…This assignment of origin is consistent with that reported for similar complexes in the literature. 21 Additionally, these data clearly showed that the charge of complexes influences the emission maximum promoting a shift from less energetic in neutral species ( 1 ) to more energetic emission in cationic species ( 2 ) as a consequence of changes in the energy of frontier orbitals. In this particular case, it can be proposed that protonation of the pyridylpyrazol renders less electron density on the Ir III metal center, lowering the energy of the HOMO orbitals 22 and blue-shifting the emission maxima from 720 to 690 nm.…”

Structural Diversity in Cyclometalated Diiridium(III) Complexes with Bridging syn and anti μ2‐Oxamidato and μ2‐Dithioxamidato Ligands

“…Cyclometalated Ir(III) complexes continue to attract great attention due to their facile chemical modifications, readily tunable photophysical and structural properties, and their high stability. [1][2][3][4][5][6][7][8][9][10] In contrast to the extensive development of monoiridium complexes that followed the initial work by Watts and co-workers in the 1980s, [11] diiridium complexes have been largely neglected, although the bridging ligand can impart additional interesting structural and electronic variations compared to monoiridium systems. [12,13] Diiridium complexes are often obtained as a mixture of diastereomers, which are generally not separated.…”