Cyclic(amino)(barrelene)carbene metal amide complexes: Synthesis and thermally activated delayed fluorescence

Carbene-metal-amide (CMA) complexes based on cyclic(amino)(barrelene)carbene (CABC) ligands have been prepared for both Cu(I) and Au(I) metal centres. Synthetic protocols based on the conventional and microwave heating enabled ten-fold shorter reaction times and high yields of the CMA materials. Stabilization of the lowest unoccupied molecular orbital (LUMO) effects the electronic and photophysical properties. These materials benefit from short excited state lifetimes down to 0.9 μs and photoluminescence quantum yields up to 66 %. Nonradiative processes are revealed and associated with the rotational freedom of the aryl moiety in the CABC carbene ligand. Steady-state and time-resolved photoluminescence spectroscopy was used to estimate an activation energy barrier of 83 meV between singlet and triplet charge transfer (CT) excited states. Varied temperature photoluminescence confirms that ³CT photoluminescence remains even at 18 K, with no contribution from locally excited triplet states ³LE. Molecular design rules have been enhanced to propose bright thermally activated delayed fluorescence (TADF) CMA emitters.