Copper and gold cyclic (alkyl)(amino)carbene complexes with sub-microsecond photoemissions: Structure and substituent effects on redox and luminescent properties

Copper and gold halide and pseudo-halide complexes stabilized by methyl-, ethyl- and adamantyl-substituted cyclic (alkyl)(amino)¬carbene (CAAC) ligands are mostly linear monomers in the solid state, without aurophilic Au···Au interactions. (Et2L)CuCl shows the highest photoluminescence quantum yield (PLQY) in the series, 70%. The photoemissions of Me2L and Et2L copper halide complexes show S1 → S0 fluorescence on the ns time scale, in agreement with theory, as well as a minor long-lived emission. Monomeric (Me2L)CuNCS is a white emitter, while dimeric [(Et2L)Cu(µ-NCS)]2 shows intense yellow emission with a PLQY of 49%. The reaction of (AdL)MCl (M = Cu or Au) with phenols ArOH (Ar = Ph, 2,6-F2C6H3, 2,6-Me2C6H3, 3,5-But2C6H3, 2-But-5-MeC6H3, 2-pyridyl), thiophenol, or aromatic amines H2NAr' (Ar' = Ph, 3,5-(CF3)2C6H3, C6F5, 2-py) afforded the corresponding phenolato, thiophenolato and amido complexes. Whereas the emission wavelengths are only marginally affected by the ring substitution pattern, the PL intensities respond sensitively to the presence of substituents in ortho or meta position. In gold aryloxides PL is controlled by steric factors, with strong luminescence in compounds with Au-O-C-C torsion angles <50. Calculations confirm the dependence of oscillator strength on the torsion angle, as well as the inter-ligand charge transfer nature of the emission. The HOMO/LUMO energy levels were estimated based on first reduction and oxidation potentials.