Self‐Assembly of ZnO Nanocrystals in Colloidal Solutions

The self‐organization in solution of ZnO nanocrystals into superlattices is monitored by dynamic light scattering. When long‐alkyl‐chain amines or carboxylic acids are used as stabilizing ligands, no organization is observed. In contrast, when binary mixtures of long‐alkyl‐chain amines and carboxylic acids are used, the presence of a thermodynamic equilibrium between free and organized ZnO nanoparticles is detected in THF or toluene. The superlattices of organized ZnO nanoparticles are independently observed by TEM and SEM. The coordination mode of the ligands at the surface of the ZnO nanoparticles is evidenced by NMR studies. The presence of ion‐paired ammonium carboxylate surrounding the surface of ZnO nanoparticles appears to be a necessary requirement to govern this reversible organization. This is substantiated by the absence of organization of ZnO nanoparticles when either a solvent of high dielectric constant, such as acetone, or a strong hydrogen‐bond acceptor is used.     

Organic Donor–Acceptor Assemblies form Coaxial p–n Heterojunctions with High Photoconductivity

The formation of coaxial p–n heterojunctions by mesoscale alignment of self‐sorted donor and acceptor molecules, important to achieve high photocurrent generation in organic semiconductor‐based assemblies, remains a challenging topic. Herein, we show that mixing a p‐type π gelator (TTV) with an n‐type semiconductor (PBI) results in the formation of self‐sorted fibers which are coaxially aligned to form interfacial p–n heterojunctions. UV/Vis absorption spectroscopy, powder X‐ray diffraction studies, atomic force microscopy, and Kelvin‐probe force microscopy revealed an initial self‐sorting at the molecular level and a subsequent mesoscale self‐assembly of the resulted supramolecular fibers leading to coaxially aligned p–n heterojunctions. A flash photolysis time‐resolved microwave conductivity (FP‐TRMC) study revealed a 12‐fold enhancement in the anisotropic photoconductivity of TTV/PBI coaxial fibers when compared to the individual assemblies of the donor/acceptor molecules.     

Vortex‐Pattern Self‐Assembly in Mn‐Doped ZnSe Nanorods

Spontaneous patterning of anisotropic nanostructures into ordered assemblies remains a challenging quest, which requires controlled innovative approaches. One way to achieve such ordering of 1D nanorods is by manipulating the varieties of interactions (attractive and repulsive forces) present in colloidal solutions of anisotropic nanocrystals. The other ingenuous pathway is solvent‐evaporation‐mediated self‐organization of the 1D nanorods. By following the second protocol, we have achieved exclusive pillar self‐assembled patterns of visible‐light‐emitting Mn‐doped ZnSe nanorods. The nanorods also exhibit intriguing vortex patterning observed by directional solvent evaporation from the nanorod solution. The effect of solvent evaporation to generate such unique morphologies on the TEM grid is discussed and the reported procedure to obtain the assembled patterns of visible‐light‐emitting, doped nanorods might be useful for future technological applications.     

Metallopolymer–Peptide Hybrid Materials: Synthesis and Self‐Assembly of Functional,Polyferrocenylsilane–Tetrapeptide Conjugates

Conjugates of poly(ferrocenyldimethylsilane) (PFDMS) with Ac‐(GA)₂‐OH, Ac‐A₄‐OH, Ac‐G₄‐OH and Ac‐V₄‐OH have been prepared by reaction of the tetrapeptide units with the amino‐terminated metallopolymer. The number average degree of polymerisation (DP_n) of the PFDMS was approximately 20 and comparable materials with shorter (DP_n≈10) and/or amorphous chains have been prepared by the same procedure. Poly(ferrocenylethylmethylsilane) (PFEMS) was employed for the latter purpose. All conjugates were characterised by GPC, MALDI‐TOF MS, NMR and IR spectroscopy. With the exception of Ac‐V₄‐PFDMS₂₀, all materials exhibited some anti‐parallel β‐sheet structure in the solid state. The self‐assembly of the conjugates was studied in toluene by DLS. The vast majority of the materials, irrespective of peptide sequence or chain crystallinity, afforded fibres consisting of a peptidic core surrounded by a PFS corona. These fibres were found in the form of cross‐linked networks by TEM and AFM. The accessibility of the chemically reducing PFS corona has been demonstrated by the localised formation of silver nanoparticles on the surface of the fibres.     

Use of Side‐Chain Incompatibility for Tailoring Long‐Range p/n Heterojunctions: Photoconductive Nanofibers Formed by Self‐Assembly of an Amphiphilic Donor–Acceptor Dyad Consisting of Oligothiophene and Perylenediimide

To tailor organic p/n heterojunctions with molecular‐level precision, a rational design strategy using side‐chain incompatibility of a covalently connected donor–acceptor (D–A) dyad has been successfully carried out. An oligothiophene–perylenediimide dyad, when modified with triethylene glycol side chains at one terminus and dodecyl side chains at the other ( 2 Amphi ), self‐assembles into nanofibers with a long‐range D/A heterojunction. In contrast, when the dyad is modified with dodecyl side chains at both termini ( 2 Lipo ), ill‐defined microfibers result. In steady‐state measurements using microgap electrodes, a cast film of the nanofiber of 2 Amphi displays far better photoconducting properties than that of the microfiber of 2 Lipo . Flash‐photolysis time‐resolved microwave conductivity measurements, in conjunction with transient absorption spectroscopy, clearly indicate that the nanofiber of 2 Amphi intrinsically allows for better carrier generation and transport properties than the microfibrous assembly of 2 Lipo .     

Gold‐Decorated Chiral Macroporous Films by the Self‐Assembly of Functionalised Block Copolymers

We describe a new and very versatile method to place chosen chemical functionalities at the edge of the pores of macroporous materials. The method is based on the synthesis and self‐assembly of inorganic block copolymers (BCPs) having chiral rigid segments bearing controllable quantities of randomly distributed functional groups. The synthesis of a series of optically active block copolyphosphazenes (PP) with the general formula [N?P(R‐O₂C₂₀H₁₂)_0.9(FG)_0.2]_n‐b‐[N?PMePh]_m (FG=‐OC₅H₄N ( 6 ), ‐NC₄H₈S ( 7 ), and ‐NC₄H₈O ( 8 )), was accomplished by the sequential living cationic polycondensation of N‐silylphosphoranimines, using the mono‐end‐capped initiator [Ph₃P?N?PCl₃][Cl] ( 3 ). The self‐assembly of the phosphazene BCPs 6 – 8 led to chiral porous films. The functionality present on those polymers affected their self‐assembly behaviour resulting in the formation of pores of different diameters (D_n=111 ( 6 ), 53 ( 7 ) and 77 nm ( 8 )). The specific functionalisation of the pores was proven by decorating the films with gold nanoparticles (AuNPs). Thus, the BCPs 6 and 7 , having pyridine and thiomorpholine groups, respectively, were treated with HAuCl₄, followed by reduction with NaBH₄, yielding a new type of block copolyphosphazenes, which self‐assembled into chiral porous films specifically decorated with AuNPs at the edge of the pores.     

Amphiphilic Janus Gold Nanoparticles Prepared by Interface‐Directed Self‐Assembly: Synthesis and Self‐Assembly

Materials with Janus structures are attractive for wide applications in materials science. Although extensive efforts in the synthesis of Janus particles have been reported, the synthesis of sub‐10 nm Janus nanoparticles is still challenging. Herein, the synthesis of Janus gold nanoparticles (AuNPs) based on interface‐directed self‐assembly is reported. Polystyrene (PS) colloidal particles with AuNPs on the surface were prepared by interface‐directed self‐assembly, and the colloidal particles were used as templates for the synthesis of Janus AuNPs. To prepare colloidal particles, thiol‐terminated polystyrene (PS‐SH) was dissolved in toluene and citrate‐stabilized AuNPs were dispersed in aqueous solution. Upon mixing the two solutions, PS‐SH chains were grafted to the surface of AuNPs and amphiphilic AuNPs were formed at the liquid–liquid interface. PS colloidal particles decorated with AuNPs on the surfaces were prepared by adding the emulsion to excess methanol. On the surface, AuNPs were partially embedded in the colloidal particles. The outer regions of the AuNPs were exposed to the solution and were functionalized through the grafting of atom‐transfer radical polymerization (ATRP) initiator. Poly[2‐(dimethamino)ethyl methacrylate] (PDMAEMA) on AuNPs were prepared by surface‐initiated ATRP. After centrifugation and dissolving the colloidal particles in tetrahydrofuran (THF), Janus AuNPs with PS and PDMAEMA on two hemispheres were obtained. In acidic pH, Janus AuNPs are amphiphilic and are able to emulsify oil droplets in water; in basic pH, the Janus AuNPs are hydrophobic. In mixtures of THF/methanol at a volume ratio of 1:5, the Janus AuNPs self‐assemble into bilayer structures with collapsed PS in the interiors and solvated PDMAEMA at the exteriors of the structures.     

Self‐Assembly of Amphiphilic Nanocrystals

Amphiphilic hybrid materials are formed from polymer‐coated semiconductor nanoparticles that simulate a surfactant‐like response (see picture). The strength and density of the surface coating are the key assembling forces driving a transition from single particles to cylindrical or vesicular superstructures.

     

Hierarchical Nanoporous Structures by Self‐Assembled Hybrid Materials Based on Block Copolymers

Hierarchical nanoporous structures are fabricated by adsorption of micelles of diblock copolymer‐templated Au‐nanoparticles onto a hydrophilic solid substrate. Gold nanoparticles are prepared using micelles (19 nm) of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) as nanoreactors. Deposition of thin films of the micellar solution, modified with a non‐selective solvent (THF), on hydrophilic surfaces leads to the formation of hierarchical nanoporous morphologies. The thin films exhibit two different pore diameters and a total pore density of 15 × 10⁸ holes per cm². The structure was analyzed in terms of topography and chemical composition using AFM, TEM and XPS measurements. The PS‐b‐P4VP template was subsequently removed by oxygen plasma etching, to leave behind metallic nanopores that mimic the original thin film morphology.

     

Controlled Self‐Assembly by Mono‐p‐sulfonatocalix[n]arenes and Bis‐p‐sulfonatocalix[n]arenes

The complexation‐induced critical aggregation concentrations of 1‐pyrenemethylaminium by mono‐p‐sulfonatocalix[n]arenes and bis‐p‐sulfonatocalix[n]arenes (n=4, 5) were systemically measured by fluorescence spectroscopy. In all cases, the complexation‐induced critical aggregation concentration decreases by about 3 times upon addition of p‐sulfonatocalix[n]arenes. However, the optimal molar ratios for the aggregation of 1‐pyrenemethylaminium by mono‐p‐sulfonatocalix[n]arenes and bis‐p‐sulfonatocalix[n]arenes are distinctly different: For mono‐p‐sulfonatocalix[n]arenes, the optimum mixing ratio for the aggregation of 1‐pyrenemethylaminium is 1:4 mono‐p‐sulfonatocalix[n]arenes/1‐pyrenemethylaminium, whereas only 2.5 molecules of 1‐pyrenemethylaminium can be bound by one cavity of bis‐p‐sulfonatocalix[n]arenes. The intermolecular complexation of mono‐p‐sulfonatocalix[n]arenes and bis‐p‐sulfonatocalix[n]arenes with 1‐pyrenemethylaminium led to the formation of two distinctly different nanoarchitectures, which were shown to be nanoscale vesicle and rod aggregates, respectively, by using dynamic laser scattering, TEM, and SEM. This behavior is also different from the fiber‐like aggregates with lengths of several micrometers that were formed by 1‐pyrenemethylaminium itself above its critical aggregation concentration. Furthermore, the obtained nanoaggregates exhibit benign water solubility, self‐labeled fluorescence, and, more importantly, temperature responsiveness.     

Evaporation‐Driven Self‐Assembly of Colloidal Silica Dispersion: New Insights on Janus Particles

The evaporation driven self‐assembly of novel colloidal silica Janus particles was evaluated by scanning electron microscopy in comparison to unfunctionalized silica particles. The cyclodextrin‐ and azobenzene‐modified compound was obtained utilizing Pickering emulsion approach, in which the particles were immobilized on solidified wax droplets and subsequently functionalized. Silica particles were modified with 3‐aminopropyl trimethoxysilane and afterward reacted with tosyl‐β‐CD or phenylazo(benzoic acid), respectively. Mesoscopic structures of the colloidal dispersions, as dried films from aqueous solution, have been investigated by scanning electron microscopy and dynamic light scattering. Interestingly, it has been observed that the Janus particles show a significantly different evaporation‐induced assembly than the unmodified particles.     

Dynamic Formation of Hybrid Peptidic Capsules by Chiral Self‐Sorting and Self‐Assembly

Owing to their versatility and biocompatibility, peptide‐based self‐assembled structures constitute valuable targets for complex functional designs. It is now shown that artificial capsules based on β‐barrel binding motifs can be obtained by means of dynamic covalent chemistry (DCC) and self‐assembly. Short peptides (up to tetrapeptides) are reversibly attached to resorcinarene scaffolds. Peptidic capsules are thus selectively formed in either a heterochiral or a homochiral way by simultaneous and spontaneous processes, involving chiral sorting, tautomerization, diastereoselective induction of inherent chirality, and chiral self‐assembly. Self‐assembly is shown to direct the regioselectivity of reversible chemical reactions. It is also responsible for shifting the tautomeric equilibrium for one of the homochiral capsules. Two different tautomers (keto‐enamine hemisphere and enol‐imine hemisphere) are observed in this capsule, allowing the structure to adapt for self‐assembly.     

Proton‐Coupled Self‐Assembly of a Porphyrin‐Naphthalenediimide Dyad

The construction of an n–p heterojunction through the self‐assembly of a dyad based on tetraphenylporphyrin (TPP) and 1,4,5,8‐naphthalenedimide (NDI) ( 1 ) is described. Proton transfer from the lysine head group of 1 to the porphyrin ring occurs concomitantly with self‐assembly into 1D nanorods in CHCl₃. TEM and AFM studies showed that the nanorods are formed by the lateral and vertical fusion of multilameller vesicles into networks and hollow ribbons, respectively. These intermediate structures transitioned to nanorods over the course of 4–6 days. Time‐resolved spectroscopy revealed that photoinduced charge separation occurs with rate constants that depend on the nature of the aggregation.