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. 2017 May 19;3(5):e1603193.
doi: 10.1126/sciadv.1603193. eCollection 2017 May.

Molecular "Surgery" on a 23-gold-atom Nanoparticle

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Free PMC article

Molecular "Surgery" on a 23-gold-atom Nanoparticle

Qi Li et al. Sci Adv. .
Free PMC article

Abstract

Compared to molecular chemistry, nanochemistry is still far from being capable of tailoring particle structure and functionality at an atomic level. Numerous effective methodologies that can precisely tailor specific groups in organic molecules without altering the major carbon bones have been developed, but for nanoparticles, it is still extremely difficult to realize the atomic-level tailoring of specific sites in a particle without changing the structure of other parts (for example, replacing specific surface motifs and deleting one or two metal atoms). This issue severely limits nanochemists from knowing how different motifs in a nanoparticle contribute to its overall properties. We demonstrate a site-specific "surgery" on the surface motif of an atomically precise 23-gold-atom [Au23(SR)16]- nanoparticle by a two-step metal-exchange method, which leads to the "resection" of two surface gold atoms and the formation of a new 21-gold-atom nanoparticle, [Au21(SR)12(Ph2PCH2PPh2)2]+, without changing the other parts of the starting nanoparticle structure. This precise surgery of the nanocluster reveals the different reactivity of the surface motifs and the inner core: the least effect of surface motifs on optical absorption but a distinct effect on photoluminescence (that is, a 10-fold enhancement of luminescence after the tailoring). First-principles calculations further reveal the thermodynamically preferred reaction pathway for the formation of [Au21(SR)12(Ph2PCH2PPh2)2]+. This work constitutes a major step toward the development of atomically precise, versatile nanochemistry for the precise tailoring of the nanocluster structure to control its properties.

Keywords: Nanoparticle; Optical Properties; nanocluster; site-specific tailoring; structure.

Figures

Fig. 1
Fig. 1. Molecular surgery on the atomically precise 23-gold-atom nanocluster by a two-step metal-exchange method: peeling off two parts of the cluster wrapper and closing the gaps with two P–C–P plasters.
(A) Schematic of the molecular surgery on [Au23(SR)16]; all carbon tails are omitted for clarity. (B) Site-specific surface motif tailoring with a two-step metal-exchange method. The transformation from [Au23(SR)16] through [Au23−xAgx(SR)16] (x ~ 1) to [Au21(SR)12(P–C–P)2]+ is revealed by single-crystal x-ray analysis. Magenta and blue, Au; gray, Ag; yellow, S; orange, P; green, C; light green, Cl. Other C and all H atoms are omitted for clarity.
Fig. 2
Fig. 2. Comparison of the [Au23(SR)16], [Au23−xAgx(SR)16], and [Au21(SR)12(P–C–P)2]+ structures.
(A) Crystal structure of [Au23(SR)16]. Left: 15-atom Au bipyramidal core. Right: Au23S16 framework. (B) Crystal structure of [Au23−xAgx(SR)16]. Left: 15-atom Au–Ag bipyramidal core. Right: Au23−xAgxS16 framework. (C) Crystal structure of [Au21(SR)12(P–C–P)2]+. Left: 15-atom bipyramidal core. Right: Au21S12(P–C–P)2 framework. Magenta and blue, Au; gray, Ag; yellow, S; orange, P; green, C. Other C and all H atoms are omitted for clarity. The counterions TOA+ and AgCl2 are also omitted.
Fig. 3
Fig. 3. Single-crystal structure and optical properties of [Au21(SR)12(P–C–P)2]+[AgCl2].
(A) The counteranion [AgCl2] and coordination of PPh2CH2PPh2 motifs. Other carbon tails and all H atoms are removed for clarity. (B) Total structure and arrangement of [Au21(SR)12(P–C–P)2]+[AgCl2] in a single-crystal unit cell. Magenta, Au; gray, Ag; yellow, S; orange, P; green, C; light green, Cl; white, H. (C) UV-Vis absorption spectrum of [Au21(SR)12(P–C–P)2]+. (D) PL spectrum of the Au21 (solid line); the PL efficiency is enhanced ~10 times compared to Au23 (dashed line). Inset shows a photograph of the Au21 sample under 365-nm UV light.
Fig. 4
Fig. 4. Metal-exchange transformation from [Au23(SR)16] to [Au21(SR)12(P–C–P)2]+ and [Au25−xAgx(SR)18].
Fig. 5
Fig. 5. DFT-calculated free energies (ΔGrxn) of elementary reaction steps of the experimentally synthesized pure and Ag-doped Au nanoclusters.
Detailed reaction network energetics analysis can be found in table S4. Inset shows the different (thermodynamically stable) doping positions of Ag in the Au15 core of the [Au23−xAgx(SR)16] clusters. The different energy levels of the [Au23−xAgx(SR)16] clusters represent the lowest-energy isomers (based on doping positions of the inset), which are also analyzed in fig. S8.

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