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When two are better than one: bright phosphorescence from non-stereogenic dinuclear iridium(III) complexes

Daniels, R.E.; Culham, S.; Hunter, M.; Durrant, M.C.; Probert, M.R.; Clegg, W.; Williams, J.A.G.; Kozhevnikov, V.N.

When two are better than one: bright phosphorescence from non-stereogenic dinuclear iridium(III) complexes Thumbnail


R.E. Daniels

S. Culham

M. Hunter

M.C. Durrant

M.R. Probert

W. Clegg

V.N. Kozhevnikov


A new family of eight dinuclear iridium(III) complexes has been prepared, featuring 4,6-diarylpyrimidines Ly as bis-N^C-coordinating bridging ligands. The metal ions are also coordinated by a terminal N^C^N-cyclometallating ligand LX based on 1,3-di(2-pyridyl)benzene, and by a monodentate chloride or cyanide. The general formula of the compounds is {IrLXZ}2Ly (Z = Cl or CN). The family comprises examples with three different LX ligands and five different diarylpyrimidines Ly, of which four are diphenylpyrimidines and one is a dithienylpyrimidine. The requisite proligands have been synthesised via standard cross-coupling methodology. The synthesis of the complexes involves a two-step procedure, in which LXH is reacted with IrCl3·3H2O to form dinuclear complexes of the form [IrLXCl(μ-Cl)]2, followed by treatment with the diarylpyrimidine LyH2. Crucially, each complex is formed as a single compound only: the strong trans influence of the metallated rings dictates the relative disposition of the ligands, whilst the use of symmetrically substituted tridentate ligands eliminates the possibility of Λ and Δ enantiomers that are obtained when bis-bidentate units are linked through bridging ligands. The crystal structure of one member of the family has been obtained using a synchrotron X-ray source. All of the complexes are very brightly luminescent, with emission maxima in solution varying over the range 517–572 nm, according to the identity of the ligands. The highest-energy emitter is the cyanide derivative whilst the lowest is the complex with the dithienylpyrimidine. The trends in both the absorption and emission energies as a function of ligand substituent have been rationalised accurately with the aid of TD-DFT calculations. The lowest-excited singlet and triplet levels correlate with the trend in the HOMO–LUMO gap. All the complexes have quantum yields that are close to unity and phosphorescence lifetimes – of the order of 500 ns – that are unusually short for complexes of such brightness. These impressive properties stem from an unusually high rate of radiative decay, possibly due to spin–orbit coupling pathways being facilitated by the second metal ion, and to low non-radiative decay rates that may be related to the rigidity of the dinuclear scaffold.


Daniels, R., Culham, S., Hunter, M., Durrant, M., Probert, M., Clegg, W., …Kozhevnikov, V. (2016). When two are better than one: bright phosphorescence from non-stereogenic dinuclear iridium(III) complexes. Dalton Transactions, 45(16), 6949-6962.

Journal Article Type Article
Acceptance Date Mar 10, 2016
Online Publication Date Mar 17, 2016
Publication Date Apr 28, 2016
Deposit Date Mar 17, 2017
Publicly Available Date Mar 28, 2017
Journal Dalton Transactions
Print ISSN 1477-9226
Electronic ISSN 1477-9234
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 45
Issue 16
Pages 6949-6962


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