Light-Activated Intercluster Conversion of an Atomically Precise Silver Nanocluster

Abstract

Noble metal nanoclusters protected with carboranes, a 12-vertex, nearly icosahedral boron–carbon framework system, have received immense attention due to their different physicochemical properties. We have synthesized ortho-carborane-1,2-dithiol (CBDT) and triphenylphosphine (TPP) coprotected [Ag42(CBDT)15(TPP)4]2– (shortly Ag42) using a ligand-exchange induced structural transformation reaction starting from [Ag18H16(TPP)10]2+ (shortly Ag18). The formation of Ag42 was confirmed using UV–vis absorption spectroscopy, mass spectrometry, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and multinuclear magnetic resonance spectroscopy. Multiple UV–vis optical absorption features, which exhibit characteristic patterns, confirmed its molecular nature. Ag42 is the highest nuclearity silver nanocluster protected with carboranes reported so far. Although these clusters are thermally stable up to 200 °C in their solid state, light-irradiation of its solutions in dichloromethane results in its structural conversion to [Ag14(CBDT)6(TPP)6] (shortly Ag14). Single crystal X-ray diffraction of Ag14 exhibits Ag8–Ag6 core–shell structure of this nanocluster. Other spectroscopic and microscopic studies also confirm the formation of Ag14. Time-dependent mass spectrometry revealed that this light-activated intercluster conversion went through two sets of intermediate clusters. The first set of intermediates, [Ag37(CBDT)12(TPP)4]3– and [Ag35(CBDT)8(TPP)4]2– were formed after 8 h of light irradiation, and the second set comprised of [Ag30(CBDT)8(TPP)4]2–, [Ag26(CBDT)11(TPP)4]2–, and [Ag26(CBDT)7(TPP)7]2– were formed after 16 h of irradiation. After 24 h, the conversion to Ag14 was complete. Density functional theory calculations reveal that the kernel-centered excited state molecular orbitals of Ag42 are responsible for light-activated transformation. Interestingly, Ag42 showed near-infrared emission at 980 nm (1.26 eV) with a lifetime of >1.5 μs, indicating phosphorescence, while Ag14 shows red luminescence at 626 nm (1.98 eV) with a lifetime of 550 ps, indicating fluorescence. Femtosecond and nanosecond transient absorption showed the transitions between their electronic energy levels and associated carrier dynamics. Formation of the stable excited states of Ag42 is shown to be responsible for the core transformation.

Stepwise Assembly of Ag42 Nanocalices Based on a MoVI-Anchored Thiacalix[4]arene Metalloligand

“… It is worthy to note that the Ag 11 bowl comprises two vertex-sharing silver trigons and five edge-sharing silver tetragons, adding an octagon as a base (Figure f), which is quite different from the triangular cupola (four trigons + three tetragons + one hexagon), 1 of 92 Johnson solids . We also observed abundant argentophilic interactions in the metallic backbone of Ag42c with the Ag···Ag distances ranging from 2.882(3)–3.425(2) Å, which further consolidate the overall Ag 42 skeleton. , Compared with the previously reported Ag 42 nanoclusters − protected by t BuS – , t BuCC – , or ortho -carborane-1,2-dithiol, the Mo-modified TC4A 4– metalloligand exhibits a macrocyclic effect in the construction of a silver nanocalix.…”

Surface environment complication makes Ag29 nanoclusters more robust and leads to their unique packing in the supracrystal lattice

“…In the past two decades, silver nanoclusters have received unprecedented attention in cluster science. 25–40 It is widely accepted that silver nanoclusters exhibit promising functionalities and intriguing physical/chemical properties that are obviously different from their gold counterparts. 27 Ag-based metal nanoclusters generally display strong photoluminescence that renders them optically active nanomaterials for sensors or biological applications.…”

Variable control of the electronic states of a silver nanocluster via protonation/deprotonation of polyoxometalate ligands

“…9 However, in contrast to the significant number of reports on stimuli-responsive Au nanoclusters, their Ag counterparts are more scarce mainly due to their low stabilities. 6 a ,10 In particular, reversible control of the electronic states of Ag nanoclusters driven by protonation/deprotonation has never been addressed.…”