Synthesis, luminescence properties and computation studies of two-coordinate N-heterocyclic carbene (NHC) copper(I) complexes bearing quinoline derivatives as ligands

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Here, we report a series of two-coordinate N-heterocyclic carbene (NHC) copper(I) complexes having monodenate NHC 1,3-bis(2,6- diisopropylphenyl)imidazol-2-ylidene) (IPr) as a σ donor and quinoline and its derivatives as π-chromophore ligands, [Cu(IPr)(Quinoline)]BF4 (P1), [Cu(IPr)(Chloroquinoline)]BF4 (P2), [Cu(IPr)(Phenylquinoline)]BF4 (P3), and [Cu(IPr)(Aminoquinoline)]BF4 (P4), (Chloroquinoline = 2,4-dichloroquinoline, Phenylquinoline = 2-phenylquinoline, Aminoquinoline = 2,4-diaminequinoline). The X-ray diffraction studies of P1 and P3 revealed the linear coordination around the copper atom. P1 and P2 exhibit the typical metal-to-ligand charge transfer (1MLCT) absorption bands in the lowest-lying energy region, while P3 and P4 show the mixed characters of ligand-to-ligand charge transfer (1LLCT) and π→π* transition. The emission wavelengths of all NHCCu(I) complexes can be fine-tuned to cover the spectral range of 419–543 nm with the main 3(π-π) emission origin in the solid state. The differences for photophysical properties of NHCCu(I) complexes were rationalized using density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations.