RESUMO
Quantized energy levels and unique optoelectronic properties of atomically precise noble metal nanoclusters (NCs) have made them important in materials science, catalysis, sensors, and biomedicine. Recent studies on the profound chemical interactions of such NCs within themselves and with ultrasmall plasmonic nanoparticles (NPs) indicate that depending on the size, shape, and composition of the second reactant, NCs can either take part in colloidal assembly without any chemical modifications or lead to products with atoms exchanged. Anisotropic NPs are a unique class of plasmonic nanomaterials as their sharp edges and protrusions show higher chemical reactivity compared to flat surfaces, often leading to site-specific growth of foreign metals and metal oxide shells. Here, using chemical interactions between gold nanotriangles (AuNTs) and Ag NCs of different compositions, we show for the first time that metal atom etching, alloying/atom exchange, and colloidal assembly can all happen at a particular length scale. Specifically, Ag25(DMBT)18 NCs (denoted as 1), upon reacting with AuNTs of â¼57 nm edge length, etch gold atoms from their sharp tips and edges. Simultaneously, the two nanosystems exchange metal atoms, resulting in Ag-doped AuNTs and AuxAg24-x(DMBT)18 (x = 1, 2). However, another Ag NC with the same metallic core, but a different ligand shell, namely, Ag25H22(DPPE)8 (denoted as 2), creates dendritic shells made of Ag, surrounding these AuNTs under the same reaction conditions. Furthermore, we show that in the case of a more reactive thiol-protected Ag NC, namely, Ag44(pMBA)30 (denoted as 3), gold etching is faster from the edges and tips, which drastically alters the identities of both the reactants. Interestingly, when the AuNTs are protected by pMBA, 3 systematically assembles on AuNTs through H-bonding, resulting in an AuNT core-Ag NC shell nanocomposite. Thus, while shedding light on various factors affecting the reactivity of Ag NCs towards AuNTs, the present study proposes a single strategy to obtain a number of bimetallic nanosystems of targeted morphology and functionality.
RESUMO
In this communication, we present the synthesis of 2-pyrene imine thiol (2-PIT)-protected Ag35 nanoclusters using a ligand exchange-induced structural transformation reaction. The formation of the nanocluster and its composition were confirmed through several spectroscopic and electron microscopic studies. The UV-vis absorption spectrum showed a set of characteristic features of the nanocluster. This nanocluster showed blue emission under UV light due to pyrene to metal core charge-transfer, and NIR emission due to charge-transfer within the metal core. This is the first report on dual emitting pyrene protected atomically precise silver nanoclusters.
RESUMO
Ab initio studies have been done at B3LYP/6-31G* level of theory to determine the structural changes on the substitution of potassium to odd-numbered all-trans conjugated polyenes ranging from C(5) to C(13). The results show that potassium is always positioned in the form of K(+) above an odd carbon other than the terminal carbons and that the stablest structural isomer is the one with K(+) lying above the central odd carbon. If a central odd carbon does not exist (as in C(11)-system), then K(+) will be positioned above the odd carbon nearest to the central carbon to achieve maximum stability. The difference in the binding energies of the isomers is generally small and it becomes insignificantly small as the carbon chain length increases so that under suitable conditions K(+) ion may be made to move between the ends of the polyene. The metal-polyene complexes are seen to have a considerably reduced HOMO-LUMO gap. Further, the interaction of potassium with the polyene not only caused a total rearrangement of the bond lengths, bond angles and dihedral angles, but also induced a bend (warping) to the polyenic fragment that pockets K(+). The structural changes and stability of the metal-polyene complexes are explained in terms of electrostatic interaction and cation-pi cloud interaction.
