Simple Cubic Packing of Gold Nanoparticles through Rational Design of Their Dendrimeric Corona

Abstract

The first simple-cubic liquid crystal was obtained by coating monodisperse Au nanoparticles (NPs) with a thick corona of amino-substituted organic dendrons. This unusual structure was determined by grazing-incidence diffraction and electron density reconstruction and explained by analyzing the radial density profile of the corona. Another novel structure is proposed for the phase preceding the cubic one: a hexagonal superlattice composed of alternating dense and sparse strings of Au NPs.

Cubic and Other3DThermotropic Liquid Crystal Phases and Quasicrystals

“…Additional 3D thermotropic phases have been found, however, in supramolecular dendrimers in which the central ''linking group'' is a small gold nanoparticle (GNP), between 1.5 and 7 nm in diameter. A BCC (Im3m) [74] and, unusually, a simple cubic phase (Pm3m) [75] were identified (Figure 7.10c). When the GNPs were functionalized with a mixture of side-on rodlike nematogens and thioalkyl chains, in addition to columnar phases, three previously unobserved 3D ordered LC phases were obtained (Figure 7.10d): a rhombohedral (R3m) [76], a simple hexagonal (P6/mmm) [77], and indeed the close-packed FCC (Fm3m) structure [77].…”

“…(c) Micellar phases based on dendronized gold nanoparticles: cubic Im3m (BCC) [74] and simple cubic Pm3m [75]. (d) Threedimensional LC phases based on gold nanoparticles jacketed with side-on attached rodlike mesogens: rhombohedral R3m [76], simple hexagonal P6/mmm [77], and cubic Fm3m (FCC) [77].…”

“…In order to explain why spherical supramolecular dendrimers pack on lattices other than Pm3n, the average radial distribution functions of volume dV/dr have been calculated for different 3D lattices with spherical motifs [13,75]. These functions give the ideal shapes of wedge-shaped molecules that would fill the unit cell of a given phase perfectly uniformly.…”

“…In the approach by Kanie et al [75], a two-shell dendritic corona was attached to 7 nm diameter GNPs. The inner layer consisted of a mixture of α-thioalkane and α-thioalkan-ω-oic acid.…”

Designing liquid-crystalline gold nanoparticles via the olefin cross-metathesis reaction

“…Literature examples include: (i) amide-bond formation between amino-based liquid-crystalline dendrons with AuNPs functionalized with carboxylic acid functions (highly ordered simple cubic phases were obtained) [8] and (ii) hydrosilylation of laterally-branched silylated mesogens onto AuNPs coated with terminal olefins (nematic phases were observed) [9]. In parallel, our group has reported the click chemistry as an elegant synthetic tool for the synthesis of liquid-crystalline AuNPs [10]: grafting first-and second-generation liquid-crystalline dendrons containing alkyne functions onto azide-based AuNPs via the Huisgen 1,3-dipolar cycloaddition reaction in the presence of copper catalyst [11] gave liquid-crystalline AuNPs which displayed smectic A phases [10].…”