Cyclometalated Ir(iii) complexes of deprotonated N-methylbipyridinium ligands: effects of quaternised N centre position on luminescenceElectronic supplementary information (ESI) available: Characterisation and theoretical studies. CCDC 1427669-1427674. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt03753k

• Main Authors: Coe, Benjamin J, Helliwell, Madeleine, Raftery, James, Sánchez, Sergio, Peers, Martyn K, Scrutton, Nigel S
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c5dt03753k

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 PF 6 − and Cl − salts. Four of the PF 6 − 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 λ max 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. The optical emission behaviour of tricationic Ir III complexes depends markedly on the position of the N -methyl unit in cyclometalating ligands.