Luminescent gold(III) thiolates: Supramolecular interactions trigger and control switchable photoemissions from bimolecular excited states

Lucy Currie, Julio Fernandez-Cestau, Luca Rocchigiani, Benoît Bertrand, Simon J. Lancaster, David L. Hughes, Helen Duckworth, Saul T. E. Jones, Dan Credgington, Thomas J. Penfold, Manfred Bochmann

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Abstract

A new family of cyclometallated gold(III) thiolato complexes based on pyrazine-centred pincer ligands has been prepared, (C^Npz^C)AuSR, where C^Npz^C=2,6-bis(4-ButC6H4)pyrazine dianion and R=Ph (1), C6H4tBu-4 (2), 2-pyridyl (3), 1-naphthyl (1-Np, 4), 2-Np (5), quinolinyl (Quin, 6), 4-methylcoumarinyl (Coum, 7) and 1-adamantyl (8). The complexes were isolated as yellow to red solids in high yields using mild synthetic conditions. The single-crystal X-ray structures revealed that the colour of the deep-red solids is associated with the formation of a particular type of short (3.2–3.3 Å) intermolecular pyrazine⋅⋅⋅pyrazine π-interactions. In some cases, yellow and red crystal polymorphs were formed; only the latter were emissive at room temperature. Combined NMR and UV/Vis techniques showed that the supramolecular π-stacking interactions persist in solution and give rise to intense deep-red photoluminescence. Monomeric molecules show vibronically structured green emissions at low temperature, assigned to ligand-based 3IL(C^N^C) triplet emissions. By contrast, the unstructured red emissions correlate mainly with a 3LLCT(SR→{(C^Npz^C)2}) charge transfer transition from the thiolate ligand to the π⋅⋅⋅π dimerized pyrazine. Unusually, the π-interactions can be influenced by sample treatment in solution, such that the emissions can switch reversibly from red to green. To our knowledge this is the first report of aggregation-enhanced emission in gold(III) chemistry.
Original languageEnglish
Pages (from-to)105–113
Number of pages9
JournalChemistry - A European Journal
Volume23
Issue number1
Early online date9 Nov 2016
DOIs
Publication statusPublished - 1 Jan 2017

Keywords

  • coordination chemistry
  • gold
  • photoluminescence
  • stacking interactions
  • supramolecular assembly
  • tridentate ligands

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