Self-assembly Process In Solution Research Articles

Two-Dimensional Optical Waveguides at Telecom Wavelengths Based on Organic Single-Crystal Microsheets of a Charge Transfer Complex.

Organic charge transfer (CT) cocrystals open a new door for the exploitation of low-dimensional near-infrared (NIR) emitters by a convenient self-assembly approach. However, research about the fabrication of sheet-like NIR-emitting microstructures that are significant for structural construction and integrated application is limited by the unidirectional molecular packing mode. Herein, via regulation of the biaxial intermolecular CT interaction, single-crystalline microsheets with remarkable NIR emission from 720 to 960 nm were synthesized via the solution self-assembly process of dithieno[3,2-b:2',3'-d]thiophene and 7,7,8,8-tetracyanoquinodimethane. The expected sheet-like structure is conducive to achieving a two-dimensional (2D) optical waveguide with an ultralow optical loss rate of 0.250 dB/μm at 860 nm. More significantly, these as-prepared organic microsheets with tunable thicknesses (h) from 100 to 1100 nm exhibit thickness-dependent NIR optical transportation performance. These findings could pave the way to a new class of low-dimensional NIR emitters for 2D photonics at telecom wavelengths.

Driving forces and molecular interactions in the self-assembly of block copolymers to form fiber-like micelles

One-dimensional (1D) nanoscale objects abundant in nature commonly possess hierarchical structures and are generally constructed via bottom-up self-assembly strategies. The unique high aspect ratio morphology of the assembled nanofibrillar materials, such as collagen, cellulose, and silk, together with highly ordered architectures, endows a range of remarkable functionalities in nature. Inspired by this hierarchical building principle, block copolymers (BCPs) have been developed and employed to engineer man-made functional 1D nanostructures and as models to study the self-assembly process. The rapid development of advanced polymerization techniques allows for the precise design of BCPs and the resulting assemblies with intensive studies on distinct structure–property–function relationships. In this Review, we summarize and discuss the formation of fiber-like micelles from the perspectives of fundamental driving forces and molecular interactions involved in the solution self-assembly process. Three main formation mechanisms are highlighted, including covalent bonding, volume exclusion, and crystallization, which are involved in the corresponding domains of coronal, interfacial, and core segments of BCPs. Two spatiotemporal levels of fiber-like assemblies are discussed. In addition, the emerging applications and a general guidance for the rational design of advanced BCPs are proposed in light of the unique traits of fiber-like micelles.

Microfluidics for the rapid and controlled preparation of organic nanotubes of bent-core based dendrimers.

Recently, bent-core molecules have emerged as excellent building blocks for the obtaining of nanostructures in solvents. Herein, we report the use of a coaxial microfluidic system as a promising tool to control the self-assembly of non-conventional bent-core amphiphiles. Moreover, a TEM study to comprehend the hierarchical self-assembly process in solution was carried out. The proposed tool provides both a cost-effective platform to save hard-to-synthesise reagents and a rapid method to screen a plethora of different parameters, i.e., THF/water ratio, residence time, concentration of the amphiphile, temperature and pH. The experiments allowed to test for the first time the suitability of microfluidics for the self-assembly of bent-core molecules, as well as the study of a range of conditions to control the assembly of different nanostructures in a rapid and controlled manner. Additionally, organic nanostructures were combined with gold nanoparticles to prepare nanocomposites with enhanced properties. Both organic and hybrid nanostructures were also obtained in the solid state. These results may inspire scientists working on supramolecular chemistry and bent-core molecules expanding the scope of microfluidic systems for the self-assembly of other low-molecular-weight compounds.

Solid-State C-S Coupling in Nickel Organochalcogenide Frameworks as a Route to Hierarchical Structure Transfer to Binary Nanomaterials.

In this work, the transfer of the flexible and easily tunable hierarchical structure of nickel organochalcogenides to different binary Ni-based nanomaterials via selective coupling of organic units was developed. We suggested the use of substituted aryl groups in organosulfur ligands (SAr) as traceless structure-inducing units to prepare nanostructured materials. At the first step, it was shown that the slight variation of the type of SAr units and synthetic procedures allowed us to obtain nickel thiolates [Ni(SAr)2]n with diverse morphologies after a self-assembly process in solution. This feature opened the way for the synthesis of different nanomaterials from a single type of precursor using the phenomenon of direct transfer of morphology. This study revealed that various nickel thiolates undergo selective C-S coupling under high-temperature conditions with the formation of highly demanding nanostructured NiS particles and corresponding diaryl sulfides. The in situ oxidation of the formed nickel sulfide in the case of reaction in an air atmosphere provided another type of valuable nanomaterial, nickel oxide. The high selectivity of the transformation allowed the preservation of the initial organochalcogenide morphologies in the resulting products.

Controlling the Interparticular Distances of Extended Non-Close-Packed Colloidal Monolayers.

A versatile method for the preparation extended, well-ordered, non-close-packed monolayers of silica nanoparticles (137 ± 4 nm diameter) with adjustable interparticle distances is presented, which is based on a simple self-assembly procedure using aqueous dispersion with different ionic strengths. It is shown that these structures can be successfully transferred to air without suffering from aggregation. Scanning electron microscopy (SEM) is used to characterize the structures after transfer into the atmosphere. These investigations were combined with a quartz crystal microbalance with dissipation (QCM-D) experiments to follow the self-assembly process in solution. The nearest-neighbor distance distribution reveals a monotonous decrease of the average nearest-neighbor distance from 290 to 200 nm with increasing ionic strength from 0.05 to 1 mM, which indicates an increased shielding of the electrostatic interaction with increasing ionic strength. The observed saturation coverages for all studied ionic strengths are well explained with an effective hard-sphere model in which the saturation coverage is limited by Coulomb repulsion. However, at ionic strengths above 1 mM, significant amounts of aggregates are found in the dried samples, suggesting that the observed aggregates at high ionic strengths are formed during the drying process caused by capillary forces between the particles. Tuning the barrier for lateral diffusion, e.g., by changing the surface morphology or functionalization of the particles will offer a route to further extend the range of particle distances. The present approach can be easily expanded to a broad range of colloidal materials on surfaces, while it only requires low-cost laboratory equipment.

Optically active sum-frequency generation as an advanced tool for chiral metallopolymer material

Metallopolymers incorporating metal ions and polytopic ligands offer the advantage to be easily obtained through a self-assembly process in solution but offer great prospects in the development of multifunctional, smart, even self-healing, materials. We have found that chiral enantiopure ligands containing bis(oxazoline) units in combination with Ni(II) salts generate well-defined thin films either by drop casting or by spin-coating and we demonstrate that the condensation process of these chiral metallosupramolecular assemblies can be characterized through optically active sum-frequency generation.

Topochemical polymerization for preparing polymer crystals

It has been challenging for preparing large-size polymer crystals from direct solution self-assembly process because of their high molecular weight, polydispersity, complex and strong intermolecular interactions. Topochemical polymerization is an important tool for synthesizing polymers in solid state, which exhibit advantages of free-solvent, environment-friendly, high yield in stereo and regional reaction as well as possibly realizing the crystal-to-crystal transformation, and would be a promising solution. In this review, we systematically summarized the molecule systems that could achieve corresponding polymer crystals through topochemical polymerization, including olefins, diacetylenes, azide-alkynes, fullerene and their derivatives, and discussed their reaction characteristics and requirements. Finally, we briefly discussed the basic characterization techniques and promising application fields of polymer crystals, and also the existing challenges and opportunities in the field of topochemical polymerization.

Modulating the Yield But Not Pathway of Protein Self-Assembly by the Surface-Layer Protein SbpA in Solution

Surface layer (S-layer) proteins form a highly ordered crystalline, yet porous, layer on the outermost cell surface of most species of bacteria and archaea. S-layers not only provide the cell a layer for protection, they are postulated to mediate several functions such as cell adhesion, drug resistance and providing a scaffold for mineralization. Thus, S-layers provide a robust in vitro model system to test our understanding of the dynamics of self-assembly pathways, as well as a biological scaffold for hierarchical assembly of nano-materials. The SbpA protein from Lysinibacillus sphaericus is a well characterized S-layer protein that forms Ca2+ dependent, 2D crystals in solution with square symmetry. Here we use ensemble techniques to study the self-assembly process in solution. We use light scattering to follow assembly kinetics and determine a phase a diagram for crystallization; moreover we use electron microscopy and SAXS to confirm that SbpA forms large crystalline sheets in solution, detectable by our assay. Surprisingly, we find that while SbpA requires a minimal amount of Ca2+ to crystallize, excess divalent ions in solution inhibit interaction between subunits and thus self-assembly. In addition, we find that the crystallization of SbpA does not require the formation of a nucleus, and that all the steps for self-assembly are energetically favorable. We propose a model in which SbpA monomers that lack significant tertiary structure aggregate rapidly in solution to form dense protein clusters, which then order into crystalline sheets.

Synthesis, Crystal Structure and Properties of a New 3D Supramolecular Metal–Organic Framework with Stable Tunnels

A flexible polycarboxyl ligand of tetrahydrofuran-2,3,4,5-tetracarboxylic acid (H4THFTCA) and a common rigid aromatic ligand of 1,10-phenanthroline (phen) have been successfully co-assembled with Cu(NO3)2·3H2O to give out a novel 3D supramolecular metal–organic framework (MOF) compound, [Cu2(THFTCA)(phen)(H2O)2·CH3CH2OH·3H2O] n (1), by a solution self-assembly process. Compound 1 has been characterized as a 2D layered coordination polymer constructed by THFTCA4− and Cu2+ ions, and the layer present a novel (3.52)(32.53.64.7) topological network. Interestingly, the layers are fused each other via strong π–π stacking interactions among adjacent ligands of the terminal phen, so that a 3D supramolecular MOF with 1D rhomboidal tunnels array is formed. The thermogravimetric analysis and corresponding powder X-ray diffraction analysis have revealed that the tunnels structure of 1 could be retained after all guest molecules are removed, and the framework could resist the collapse even heating up to 210 °C. An opinion has also been proposed that the larger accessible volume of the guests means the larger stress on the backbone of the MOF after the guests are removed, and the stress is harmful to the stability of the supramolecular porous structure. Finally, the application properties based on the porous structure have also been primarily evaluated.

Characterization of Dielectric Nanocubes Ordered Structures Fabricated by Solution Self-Assembly Process

Characterization of Dielectric Nanocubes Ordered Structures Fabricated by Solution Self-Assembly Process

Characterization of Dielectric Nanocubes Ordered Structures Fabricated by Solution Self-Assembly Process

Ordered structures of barium titanate (BT) nanocubes, strontium titanate (ST) nanocubes and BT–ST nanocube mixture were directly fabricated on Si and Pt-coated Si substrates using a colloidal solution assembly method inspired by convection self-assembly. BT/ST alternating layered structure was also fabricated by repeating the self-assembly process several times. The microstructure of the self-assembled structures was observed using field emission scanning electron microscopy (FE-SEM) and scanning probe microscopy (SPM). It was revealed that nanocubes were arranged with various degrees of ordering to develop monolayer regions at the surface of the substrates. The crystallographic phase and orientation of the assembly consisting of BT and ST nanocubes were evaluated by X-ray diffraction analysis. The (100) and (200) diffractions of BT and ST were observed and no other diffractions were observed. The BT and ST nanocubes had a 100 face and were arrayed orderly with their faces parallel to the surface of the substrates. The piezoresponse properties obtained by scanning probe microscopy (SPM) indicated that the heterointerface between BT and ST nanocubes would introduce an anomaly in piezoelectric properties.

Programming the Supramolecular Helical Polymerization of Dendritic Dipeptides via the Stereochemical Information of the Dipeptide

Many natural biomacromolecules are homochiral and are built from constituents possessing identical handedness. The construction of synthetic molecules, macromolecules, and supramolecular structures with tailored stereochemical sequences can detail the relationship between chirality and function and provide insight into the process that leads to the selection of handedness and amplification of chirality. Dendritic dipeptides, previously reported from our laboratory, self-assemble into helical porous columns and serve as fundamental mimics of natural porous helix-forming proteins and supramolecular polymers. Herein, the synthesis of all stereochemical permutations of a self-assembling dendritic dipeptide including homochiral, heterochiral, and differentially racemized variants is reported. A combination of CD/UV-vis spectroscopy in solution and in film, X-ray diffraction, and differential scanning calorimetry studies in solid state established the role of the stereochemistry of the dipeptide on the thermodynamics and mechanism of self-assembly. It was found that the highest degree of stereochemical purity, enantiopure homochiral dendritic dipeptides, exhibits the most thermodynamically favorable self-assembly process in solution corresponding to the greatest degree of helical order and intracolumnar crystallization in solid state. Reducing the stereochemical purity of the dendritic dipeptide through heterochirality or by partially or fully racemizing the dendritic dipeptide destructively interferes with the self-assembly process. All dendritic dipeptides were shown to coassemble into single columns regardless of their stereochemistry. Because these columns exhibit no deracemization, the thermodynamic advantage of enantiopurity and homochirality suggests a mechanism for stereochemical selection and chiral amplification.

Self-assembly of dilacunary building blocks into high-nuclear [Ln16As16W164O576(OH)8(H2O)42]80−(Ln = EuIII, GdIII, TbIII, DyIII, and HoIII) polyoxotungstates

A new family of [Ln16As16W164O576(OH)8(H2O)42]80− (Ln = EuIII, GdIII, TbIII, DyIII, and HoIII) nanoclusters has been synthesized from a self-assembly process in solution. The novel macroanion is constituted of two identical sub-units with the formula [Gd8As8W82O288(OH)4(H2O)21]40− and it was obtained from the versatile building block [As2W19O67(H2O)]14− in combination with mid to late lanthanoid cations. All compounds have been structurally characterized and the magnetic properties of the Gd-containing member of the series have been investigated. The novel macroanion represents the largest polyoxotungstate reported to date and the influence of the templating cations on the molecular architecture is discussed. Furthermore, the spectrum of lanthanide linkers for the construction of large polyoxotungstates has been amplified in the present approach.

Formation of helical superstructures from a semi-fluorinated alkoxysilane through a surface and solution self-assembly process

Helical superstructures were obtained through a surface and solution self-assembly process when a semi-fluorinated alkoxysilane modified silicon wafer was immersed in water of pH values ranging from 5.0 to 7.0 for more than one month.