Luminescent Cyclometalated Dialkynylgold(III) Complexes of 2‐Phenylpyridine‐Type Derivatives with Readily Tunable Emission Properties

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Abstract
A novel class of luminescent dialkynylgold(III) complexes containing various phenylpyridine and phenylisoquinoline‐type bidentate ligands has been successfully synthesized and characterized. The structures of some of them have also been determined by X‐ray crystallography. Electrochemical studies demonstrate the presence of a ligand‐centered reduction originating from the cyclometalating C^N ligand, whereas the first oxidation wave is associated with an alkynyl ligand‐centered oxidation. The electronic absorption and photoluminescence properties of the complexes have also been investigated. In dichloromethane solution at room temperature, the low‐energy absorption bands are assigned as the metal‐perturbed π–π* intraligand (IL) transition of the cyclometalating C^N ligand, with mixing of charge‐transfer character from the aryl ring to the pyridine or isoquinoline moieties of the cyclometalating C^N ligand. The low‐energy emission bands of the complexes in fluid solution at room temperature are ascribed to originate from the metal‐perturbed π–π* IL transition of the cyclometalatng C^N ligand. For complex 4 that contains an electron‐rich amino substituent on the alkynyl ligand, a structureless emission band, instead of one with vibronic structures as in the other complexes, was observed, which was assigned as being derived from an excited state of a [π(CCC6H4NH2)→π*(C^N)] ligand‐to‐ligand charge‐transfer (LLCT) transition.