Au13 Superatom Bearing Two Terpyridines at Coaxial Positions: Photoluminescence Quenching via Complexation with 3d Metal Ions

A gold cluster [Au13(dppe)5(EPTpy)2]3+ (dppe = 1,2-bis(diphenylphosphino)ethane, EPTpy-H = 4'-(4-ethynylphenyl)-2,2':6',2''-terpyridine) was synthesized by ligand exchange reaction of [Au13(dppe)5Cl2]3+. Single-crystal X-ray diffraction analysis revealed that two terpyridyl moieties were σ-bonded to the coaxial positions of the icosahedral Au13 core. These two terpyridyl moieties were coordinated with 3d metal ions M2+ (M = Co, Ni, Cu, Zn) in acetonitrile solution under ambient conditions. The photoluminescence (PL) of [Au13(dppe)5(EPTpy)2]3+ with a quantum yield of 0.17 at ~780 nm was almost completely quenched by coordination with Co2+, Ni2+, and Cu2+, while the PL was not affected by Zn2+ coordination. The metal-dependent PL quenching behavior is ascribed to the difference in the electronic structure of the metal ions. The energy transfer from the Au13 chromophore to the coordinated Co2+, Ni2+, or Cu2+ with an open electronic structure proceeds efficiently via an electron exchange mechanism, while the process is prohibited for Zn2+ with a closed electronic structure. Two terpyridine-functionalized alkynyl ligands were successfully introduced at the diagonal apex sites of an icosahedral Au13 superatom. 3d metal ions (Co2+, Ni2+, Cu2+, Zn2+) were coordinated to the terpyridyl groups, leading to the dimerization of the Au13 superatoms by chelation and to the photoluminescence quenching specific to Co2+, Ni2+, or Cu2+ ions.