Diphosphine-induced chiral propeller arrangement of gold nanoclusters for singlet oxygen photogeneration

In this study, 1, 2-bis(diphenylphosphino)ethane (dppe) ligands are used to synthesize gold nanoclusters with an icosahedral Au₁₃ core. The nanoclusters are characterized and formulated as [Au₁₃(dppe)5Cl₂]Cl₃ using synchrotron radiation X-ray diffraction, UV/Vis absorption spectroscopy, electrospray ionization mass spectrometry, and density functional theory (DFT) calculations. The bidentate feature of dppe ligands and the positions of coordinating surface gold atoms induce a helical arrangement that forms a propeller-like structure, which reduces the symmetry of the gold nanocluster to C₁. Therefore, dppe ligands perform as a directing agent to create chiral an ansa metallamacrocycle [Au₁₃(dppe)₅Cl₂]³⁺ nanocluster, as confirmed by simulated electronic circular dichroism spectrum. The highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of the [Au₁₃(dppe)₅Cl₂]³⁺ cluster is determined as approx. 1.9 eV, and further confirmed by ultraviolet photoemission spectroscopy analysis and DFT simulation. Furthermore, the photoactivity of [Au₁₃(dppe)₅Cl₂]³⁺ is investigated, with the nanocluster shown to possess near-infrared photoluminescence properties, which can be employed for ¹O₂ photogeneration. The quantum yield of ¹O₂ photogeneration using the [Au₁₃(dppe)₅Cl₂]³⁺ nanocluster is up to 0.71, which is considerably higher than those of anthracene (an organic dye), and Au₂₅ and Au₃₈ nanoclusters.