Light-Triggered Reversible Supracolloidal Self-Assembly of Precision Gold Nanoclusters

Abstract

Monolayer thiol-protected noble metal nanoclusters are attractive nanoscale building blocks for well-defined colloidal superstructures. However, achieving facile reversible self-assembly of nanoclusters using external stimuli is still in its infancy. Herein, we report the synthesis and photon-assisted reversible self-assembly of thiolated azobenzene-stapled Au25 nanoclusters. Photoactivation of functionalized nanoclusters in dichloromethane by irradiating ultraviolet light at 345 nm resulted in a visual change and formation of disc-like colloidal superstructures (d ~100 -1000 nm). The superstructures readily disassembled into individual nanoclusters upon irradiating with the visible light at 435 nm. Systematic changes in both the electronic absorption bands and nuclear magnetic resonance spectra of chromophores in solution suggest that the self-assembly is driven by the photoisomerization of surface ligands. High-resolution transmission electron microscopy, electron tomographic reconstruction, dynamic light scattering, and small-angle X-ray powder diffraction show that the disc-like superstructures contain densely packed nanoclusters. Long-range self-assembly and disassembly under ultraviolet and visible light, respectively demonstrate reversible photo-switching in nanoclusters.NCs). Dried [Au25(C3-AMT)18] -NCs were stored at 4 ºC for further characterizations. ASSOCIATED CONTENT Supporting InformationThe Supporting Information is available free of charge on the ACS Publications website. Scheme S1, S2 and Figures S1-S17 as described in the text (PDF) Video S1 as described in the text (MOV)

Molecular reactivity of thiolate-protected noble metal nanoclusters: synthesis, self-assembly, and applications

“…Rival et al developed a light-triggered strategy for stacking thiolated azobenzene-protected Au 25 NCs into disk-like superstructures, where light-switchable dipole–dipole interactions of azobenzene govern the self-assembly behaviour of NCs. 193 Moreover, H-bonds have also been employed by Nonappa et al for packing Au 102 ( p -MBA) 44 into 2D nanosheets, which can be further bent into spherical capsids or stacked into faceted multi-layers ( Fig. 7c ).…”

Self‐Assembly of Precision Noble Metal Nanoclusters: Hierarchical Structural Complexity, Colloidal Superstructures, and Applications

“…investigated the photon‐assisted switchable self‐assembly in [Au 25 (C 3 ‐AMT) 18 ] − NCs using two different wavelengths of light. [ 313 ] The modified Brust–Schiffrin method [ 96 ] was used to synthesize the kinetically controlled Au 25 NCs using C 3 ‐AMT as the protecting ligand. Photoisomerization of [Au 25 (C 3 ‐AMT) 18 ] − NCs under visible (435 nm) and ultraviolet (345 nm) lights has shown systematic changes in the optical absorption bands and chemical shifts in NMR spectra.…”

Photo-assembly of plasmonic nanoparticles: methods and applications

“…In another approach, small gold nanoclusters (Au 25 ) were coated with azobenzene C3 alkyl monothiol. 39 It was found that for such a system, a transformation from trans to cis form is realized aer exposure to 345 nm light, and the reverse process is observed aer exposure to 435 nm light. Attractive dipoledipole interactions, which occur only for the cis form, lead to a self-assembly of nano-clusters covered with ligands containing the azobenzene moiety in the cis form.…”