Direct Control of the Spatial Arrangement of Gold Nanoparticles in Organic–Inorganic Hybrid Superstructures

Abstract

The directed assembly of gold nanoparticles is essential for their use in many kinds of applications, such as electronic devices, biological labels, and sensors. Herein an atomic alteration in the molecular structure of ligand-stabilized gold nanoparticles that can shift the interparticle distance up to 1 nm upon covalent coupling to organic-inorganic superstructures is presented. Gold nanoparticles are stabilized by two octadentate thioether ligands and have a mean diameter of 1.1 nm. The ligands contain a central rigid rod varying in length and terminally functionalized with a protected acetylene. The two peripheral functional groups on each particle enable the directed assembly of nanoparticles to dimers, trimers, and tetramers by oxidative acetylene coupling. This is a wet chemical protocol resulting in covalently bound nanoparticles. These organic-inorganic hybrid superstructures are analyzed by transmission electron microscopy, small angle X-ray scattering, and UV/vis spectroscopy. The focus of the comparison here is the subunit, which is anchoring the bridgehead, either a pyridine or benzene moiety. The pyridine-based ligands reflect the calculated length of the rigid-rod spacer in their interparticle distances in the obtained hybrid structures. This suggests a perpendicular arrangement that results from the coordination of the pyridine's lone pair to the gold surface. An atomic variation in the ligand's center leads to smaller interparticle distances in the case of hybrid structures obtained from benzene ligands. This large difference in the spatial arrangement suggests a tangential arrangement of the interparticle bridging structure in the latter case. Consequently a rather flat arrangement parallel to the particle surface must be assumed for the central benzene unit of the benzene-based ligand.

Size Matters: Influence of Gold‐to‐Ligand Ratio and Sulfur‐Sulfur Distance of Linear Thioether Heptamers on the Size of Gold Nanoparticles

“…Interestingly, already the reaction with eight equiv. of the gold salt featured a slight reddish hue, pointing towards larger AuNPs compared to previously reported NPs, which themselves were – with eight equiv. of gold salt – dark brown in solution.…”

“…An adapted protocol of the two‐phase Brust–Schiffrin method was used to synthesize AuNPs stabilized by the here investigated heptamers ( Xyl , TPM , and Ter , see Scheme ). The main difference to our former studies on thioether stabilized AuNPs was that the molar ratio of ligand to gold salt was varied. So far we kept the growth conditions for the particles as uniform as possible enabling the comparison of stabilization features due to the ligands design and thus, a 1:1 molar ratio of thioether moieties to gold equiv.…”

“…Inspired by this concept, we explored various multidentate macromolecules like linear oligomers, and dendritic systems for the stabilization of small NPs. The low integer number of molecules per NPs decorated with a masked ethynyl moieties allowed mono‐ or bifunctionalized NPs to create supramolecular dumbbell, trikes and quads or linear pearl‐necklace hybrid materials via mild acetylene homo‐coupling or acetylene/azide‐click reactions. What is strikingly conspicuous however is the fact that all these macromolecule‐coated NPs feature almost the same sizes around 1 – 1.3 nm with barely noticeable SPR‐bands (UV/VIS), and have thus limited potential for optical sensing applications.…”

Gold Nanoparticle Assemblies on Surfaces: Reactivity Tuning through Capping‐Layer and Cross‐Linker Design

“…[9][10][11][12] For instance, island-like films constructed from metal NPs were shown to have different physical, electronic, and opticalp roperties relative to continuous films. [18][19][20][21] The combination of many parameters, including the size, capping layer,s olvent, electronic properties, and noncovalentinteractions,plays ak ey role in NP aggregation. [16,17] In spite of recent progress, defining the rules that control the surface organizationo fN Ps with molecular cross-linkers is still ac hallenge.…”

Phenyl–Acetylene Bond Assembly: A Powerful Tool for the Construction of Nanoscale Architectures

“…This microreview describes synthetic strategies for the formation of suitable building blocks geared towards the assembly of larger molecular architectures. The structural motif of phenyl–acetylene bonds finds use in applications as diverse as molecular electronics,9 nano‐sensors,10 liquid crystals,11 natural products,12,13 optoelectronics,14 organic‐inorganic hybrid structures,15,16 surface functionalisation17 and cell imaging,18 amongst many others. In many instances acetylene couplings are preferential to Suzuki19 or Stille20 direct sp 2 –sp 2 couplings because they can be essential for achieving coplanarity, for increasing π‐conjugation lengths and for decreasing HOMO–LUMO gaps.…”