Gold Nanoparticles Stabilized by Single Tripodal Ligands

Abstract

have been investigated, ranging from oligomeric, [28][29][30][31][32][33] tripodal, [34,35] and dendrimeric [36][37][38][39][40][41] to even cage-like [42] thioether-based ligands, most of them yielding AuNPs with narrow size distributions. Cages controlling the size of the nanoparticles were also developed for other noble metals like palladium, displaying catalytic activity. [43][44][45] Also, the periodically arranged cavities of a covalent organic framework were used as "caging" structure for catalytically active palladium and platinum particles. [46] It has furthermore been shown that such oligomeric benzyl sulfide ligand-stabilized AuNPs are accessible by wet chemical procedures, and ligand-coated AuNPs exposing reactive functional groups have been interlinked forming nanoarchitectures. [29][30][31]37,38] In the approach, the ligand not only controls the particles' sizes, but also the number and the spatial orientation of exposed functional groups.While rather complex and synthetically demanding dentritic ligands already displayed their ability to stabilize an entire AuNP, [36][37][38][39] a more recent ligand design showed that also linear oligomers are able to stabilize an entire particle when bulky enough to sterically protect the surface of the ligand-coated AuNP. [32] With a series of linear oligomers of various sulfursulfur distances, a correlation between the size of the stabilized AuNP and both parameters, the distance between coordination points of these multivalent ligand structures and the equivalents of gold salt used has been observed. [33] The study, however, also unraveled some limitations of the approach, namely an increasing loss over the control of the NP's size going along with a decrease in the stability of these AuNPs with increasing size.An alternative approach to increase both the number of coordinating sulfide groups and the AuNP surface covered by the ligand is the use of suitable branching points, increasing the number of oligomeric branches per ligand. Further, such architectures break the linearity of the ligand, enabling better coverage of the surface of AuNPs upon passivation. Of particular interest was to which extent a local density of concave, pre-organized coordinating sites might steer the dimensions of the stabilized particle.Already slightly larger AuNPs with diameters in the order of about 2 nm display surface plasmon bands and are thus interesting target structures opening the door for sensing and labeling applications. [3] The here reported research is motivated by our interest in optically active, ligand-stabilized AuNPs with a controlled exposition of functional groups as potential building blocks for hybrid nanoarchitectures interacting with optical signals.In order to benefit from surficial rather than linear coverage, we introduce a central tetraphenylmethane-based tripodal unit, which interlinks three oligomeric side-chains. In addition, the In order to coat the entire surface of gold nanoparticles (AuNPs) by a single ligand, tripodal macromolecules comprising be...

Prospects of Coupled Organic–Inorganic Nanostructures for Charge and Energy Transfer Applications

“…[92] Especially charged anchor groups with ah igh coordinative character (e.g.c arboxyls) are susceptible to changes in pH and salt concentration. While multidentate as well as multipodal binding schemes strengthen the mechanical binding via chelate effects,e specially multipodal anchors often contain conjugation breakers such as sp 3 hybridized carbon atoms [93] and higher denticities, [94] such as macrocyclic layouts are comparably rare. [95] Ligands are either already present during wet-chemical NC growth or introduced at al ater stage via exchange reactions (post-modification).…”

Monofunctionalized Gold Nanoparticles: Fabrication and Applications

“…[51] Introduction of an exposed alkyne group at the central dendrimer subunit provided dumbbell-type AuNP dimers upon oxidative acetylene coupling [52] and trimeric or tetrameric AuNP architectures upon exposure to copper(i)-catalyzed alkyne-azide cycloaddition (CuAAC) 'click' reaction conditions with central linking units comprising three or four benzylic azides respectively, [53] all corroborating the 1:1 dendrimer:AuNP ratio. Enlarging the steric demand of the coating benzyl thioether ligand by tetraphenylmethane subunits even provided linear [28] and threefold branched [29] oligomers able to coat entire AuNPs. The central tetraphenyl subunit of the latter was ideally suited to expose a single alkyne group enabling again the formation of AuNP dimers or trimers by wet chemical protocols based on oxidative acetylene homocoupling or CuAAC respectively (Fig.…”

“…The most straightforward way to synthesize monofunctionalized AuNPs is to design ligands that are large enough to stabilize an entire particle by steric crowding, [25][26][27][28][29] yet the introduction of a single functional unit per ligand demands sophisticated synthetic strategies.…”

Perspektiven gekoppelter organisch‐anorganischer Nanostrukturen für Ladungs‐ und Energietransferanwendungen

“…Mehrzähnige und -füßige Bindungsschemata verstärken zwar die mechanische Bindung über Chelat-Effekte, jedoch enthalten insbesondere mehrfüßige Anker oft Konjugations-unterbrechende Strukturen wie sp 3 -hybridisierte Kohlenstoffatome. [93] Hçhere Zähnigkeiten, [94] z. B. Makrocyclen, sind vergleichsweise selten.…”