ABSTRACT
Intrinsic dual-emission (DE) of gold nanoclusters in the near-infrared (NIR) are fascinating for fundamental importance and practical applications, but their synthesis remains a formidable challenge and sophisticated excited-state processes make elucidating DE mechanisms much more arduous. Here, we report an all-alkynyl-protected gold nanocluster, Au20, showing a prolate Au12 tri-octahedral kernel surrounded by two Au2(CZ-PrA)3 dimers, four Au(CZ-PrA)2 monomers, and two CZ-PrA- bridges. Au20 exhibits distinguished photophysical properties including NIR DE at 820 and 940 nm, microsecond radiative relaxation, and 6.26% photoluminescent quantum yield at ambient environment in nondegassed solution. Combining systematic studies on steady/transient spectroscopy and theoretical calculation, we identified two triplet charge transfer (CT) states, ligand-to-kernel and kernel-based CT states as DE origins. Furthermore, this NIR DE exhibits highly independent and sensitive response to surrounding environments, which well coincide with its mechanism. This work not only provides a substantial structure model to understand a distinctive DE mechanism but also motivates the further development of NIR DE materials.
ABSTRACT
Thiacalix[4]arenes have emerged as a family of macrocyclic ligands to protect metal nanoparticles, but it remains a great challenge to solve the mystery of their structures at the atomic level, especially for those larger than 2â nm. Here, we report the largest known mixed-valence silver nanocluster [Ag155 (CyS)40 (TC4A)5 Cl2 ] (Ag155) protected by deprotonated cyclohexanethiol (CySH) and macrocyclic ligand p-tert-butylthiacalix[4]arene (H4 TC4A). Its single-crystal structure consists of a metallic core of four concentric shells, Ag13 @Ag42 @Ag30 @Ag70 , lined with a organic skin of 40CyS- and 5TC4A4- and 2Cl- . Ag155 manifests an unusual pseudo-5-fold symmetry dictated by the intrinsic metal atom packing and the regioselective distribution of mixed protective ligands. This work not only reveals a macrocyclic ligand effect on the formation of a large silver nanocluster, but also provides a new structural archetype for comprehensively perceiving their interface and metal kernel structures.
ABSTRACT
The structural transformations of metal nanoclusters are typically quite complex processes involving the formation and breakage of several bonds, and thus are challenging to study. Herein, we report a case where two lacunary Keggin polyoxometallate templated silver single-pods [PW9O34@Ag51] (SD/Ag51b) fuse to a double-pod [(PW9O34)2@Ag72] by reacting with 4,4'-bipyridine (bipy) or 1,4-bis(4-pyridinylmethyl)piperazine (pi-bipy). Their crystal structures reveal the formation of a 2D 44-sql layer (SD/Ag72a) with bipy and a 3D pcu framework (SD/Ag72c) with pi-bipy. The PW9O349- retains its structure during the cluster fusion and cluster-based network formation. Although the two processes, stripping of an Ag-ligands interface followed by fusion, and polymerization, are difficult to envisage, electrospray ionization mass spectrometry provides enough evidences for such a proposal to be made. Through this example, we expect the structural transformation to become a powerful method for synthesizing silver nanoclusters and their infinite networks, and to evolve from trial-and-error to rational.
ABSTRACT
Herein, we report a 78-nuclei silver nanocluster (NC) [Ag78 (i PrPhS)30 (dppm)10 Cl10 ]4+ (SD/Ag78a; dppm=bis-(diphenylphosphino)methane) that was synthesized through a one-pot reaction using [Ag(pz)]n as precursor (Hpz=pyrazole) and further characterized by X-ray crystallography. SD/Ag78a shows a core-shell structure comprised of an all-metallic Ag53 kernel surrounded by an Ag25 discontinuous metal-organic shell. The Ag53 kernel is an Ag13 Ino decahedron encaged by an Ag40 drum-like shell, while the Ag25 shell consists of two Ag10 S10 P10 Cl5 rings and five S-Ag-S staples. Three types of ligands regioselectively cap on the surface of the Ag78 NC, forming diverse metal-ligand interfacial structures. The NC is a closed-shell 34-electron superatom with +4 charge state and shows highly featured molecule-like absorption spectra in the UV/Vis region with a maximum around 493â nm. The rhombic superlattice assembled from SD/Ag78a through intercluster C-Hâ â â π interactions can be formed by a simple drop-casting treatment.
