Cyclometalated Ir(iii) complexes of deprotonated N-methylbipyridinium ligands: effects of quaternised N centre position on luminescence

Abstract

Six new tricationic Ir(III) complexes of cyclometalating ligands derived from 1-methyl-2-(2'-pyridyl)pyridinium or 1-methyl-4-(2'-pyridyl)pyridinium are described. These complexes of the form [Ir(III)(C^N)2(N^N)](3+) (C^N = cyclometalating ligand; N^N = α-diimine) have been isolated and characterised as their PF6(-) and Cl(-) salts. Four of the PF6(-) salts have been studied by X-ray crystallography, and structures have been obtained also for two complex salts containing MeCN and Cl(-) or two Cl(-) ligands instead of N^N. The influence of the position of the quaternised N atom in C^N and the substituents on N^N on the electronic/optical properties are compared with those of the analogous complexes where C^N derives from 1-methyl-3-(2'-pyridyl)pyridinium (B. J. Coe, et al., Dalton Trans., 2015, 44, 15420). Voltammetric studies reveal one irreversible oxidation and multiple reduction processes which are mostly reversible. The new complexes show intramolecular charge-transfer absorptions between 350 and 450 nm, and exhibit bright green luminescence, with λmax values in the range 508-530 nm in both aqueous and acetonitrile solutions. In order to gain insights into the factors that govern the emission properties, density functional theory (DFT) and time-dependent DFT calculations have been carried out. The results confirm that the emission arises largely from triplet excited states of the C^N ligand ((3)LC), with some triplet metal-to-ligand charge-transfer ((3)MLCT) contributions.

Iridium(III) Complexes Bearing a Formal Tetradentate Coordination Chelate: Structural Properties and Phosphorescence Fine-Tuned by Ancillaries

“…Overall, the three N atoms of N3C chelates are arranged in the meridional mode, while the phenyl appendage is located at the axial site vs the plane defined by the meridional arranged N atoms and is located at the trans disposition to the unique chloride, leaving the monodentate N donor to occupy the remaining coordination site that is trans to the central pyridine unit of N3C chelate. The unique Ir−C distances of 2.005(4) Å in 3 and 2.015(5) Å in 5 are similar to the reported Ir−C bond distances trans to the chloride, 37 while the py and mpzH ligands of 3 and 5 exhibited the longest Ir− N distances within each molecule, i.e., 2.067(3) and 2.052(4) Å, which could be due to the strong trans influence exerted by the central pyridine unit of the N3C chelate, which exhibited the shortest Ir−N distance, i.e., 2.007(3) and 2.005(4) Å.…”

Light-driven biocatalytic reduction of α,β-unsaturated compounds by ene reductases employing transition metal complexes as photosensitizers

“…Also, [Ir(Me-2,2′-bpy) 2 (bpy)] 3+ and [Ir(Me-3,2′-bpy) 2 (dCF 3 bpy)] 3+ were chosen from a series of highly water soluble Ir( iii ) cyclometalated complexes ( Scheme 3 ). 46 , 47 [Ru(bpy) 3 ] 2+ was employed as a control standard, and Cl – salts were used in all cases. In each case, reactions were performed with cyclohexen-2-one as the enzyme oxidative substrate.…”

Regioisomerism in cationic sulfonyl-substituted [Ir(C^N)2(N^N)]+ complexes: its influence on photophysical properties and LEC performance

“…There have been few investigations on the influence of the substitution position of ligand functionalities on the properties of [Ir(C^N) 2 (N^N)] + complexes. Examples include the introduction of diphenylamino, 25 fluoro, 26 methyl, 27 trifluoromethyl, 28,29 methylpyridinium, 30 bromo and fluorenyl 31 and benzylsulfonyl 15 groups in the 3-, 4-and 5-positions of the cyclometallating phenyl ring. In all of these studies, except for the one investigating bromo and fluorenyl groups, 31 it was found that substitution in the 4-position, i.e.…”