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.