Panchromatic Gold Alkynyl Complexes with Pyrenyl-N-Heterocyclic Carbene Ligand Displaying Anti-Kasha Behavior

A unique family of alkynyl-gold(I)-complexes (1-6) containing pyrenyl-NHC chromophoric ligand (NHC = N-heterocyclic carbene) has been prepared and fully characterized. The complexes were engineered such that a pyrenyl ligand was introduced to one nitrogen center of the carbene unit while to the other nitrogen center we attached a methyl (1), n-butyl (2), or naphthyl (3-6) group in order to probe their effect on the photophysical properties of our Au-alkynyl complexes. For comparison purposes the cyanide-gold(I) complex (7) was prepared and fully characterized. The molecular structures of 3 and 4 and 7 were ascertained by X-ray diffraction study. In stark contrast to the alkynyl complexes, the cyano-Au complex 7 displayed only weak fluorescence highlighting the impact of the -C≡C─Ar unit on their emission properties. The alkynyl complexes displayed different behavior, for instance, complex 1 exhibited excimer emissions originated from the pyrene chromophore while compound 2-6 displayed remarkable multi-emissive properties, mainly 3-6 showing panchromatic behavior with emissions dependent on the excitation wavelengths suggesting anti-Kasha behavior. TD-DFT-calculations were carried out to support interpretation of the experimental results. These remarkable results have not been observed previously, making these molecules important candidates for a wide range of applications in the optical domain.