Controlled Self-Assembly Manipulated by Charge-Transfer Interactions: From Tubes to Vesicles

Responsive Interfacial Assemblies Based on Charge-Transfer Interactions

Charge transfer (CT) interactions have been widely used to construct supramolecular systems, such as functional nanostructures and gels. However, to date, there is no report on the generation of CT complexes at the liquid-liquid interface. Here, by using an electron-deficient acceptor dissolved in water and an electron-rich donor dissolved in oil, we present the in situ formation and assembly of CT complex surfactants (CTCSs) at the oil-water interface. With time, CTCSs can assemble into higher-order nanofilms with exceptional mechanical properties, allowing the stabilization of liquids and offering the possibility to structure liquids into nonequilibrium shapes. Moreover, due to the redox-responsiveness of the electron-deficient acceptor, the association and dissociation of CTCSs can be reversibly manipulated in a redox process, leading to the switchable assembly and disassembly of the resultant constructs.

Evanescent Wave-Guided Growth of an Organic Supramolecular Nanowire Array

The ordered assembly of molecules within a specific space of nanoscale, such as a surface, holds great promise in advanced micro-/nanostructure fabrication for various applications. Herein, we demonstrate the evanescent wave (EW)-guided organization of small molecules into a long-range ordered nanowire (NW) array. Experiment and simulation revealed that the orientation and periodicity of the NW array were feasibly regulated by altering the propagation direction and the wavelength of EW. The generality of this approach was demonstrated by using different molecule precursors. While existing studies on EW often took advantages of its near-field property for optical sensing, this work demonstrated the photochemical power of EW in the guided-assembly of small molecules for the first time. It also provides an enlightening avenue to periodic structure with fluorescence, promising for super-resolution microscopy and important devices applicable to optical and bio-related fields.

Three-dimensional directed assembly of organic charge-transfer heterostructure

Multicomponent crystalline heterostructures are a powerful approach to integrate different functional materials into the ordered structures. Here we describe three-dimensional spherical assembly of binary organic solids that consist of electron donor and acceptor molecules. A mechanistic study of heterostructure formation reveals that the dewetting and drying-mediated assembly processes are responsible for the spherical crystallite formation. The assembled spherical heterostructures are highly tunable, crystalline and chemically stable, exhibiting phase separation controlled optoelectronic behavior. This simple, generalizable three-dimensional assembly can be modified for the formation of ordered functional organic multicomponent heterostructures for emerging applications.

Controlled self-assembly into diverse stimuli-responsive microstructures: from microspheres to branched cylindrical micelles and vesicles

A series of amphiphilic PDMAEMA-SS-PCL chains with variable ratios of hydrophilic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) to hydrophobic poly(ε-caprolactone) (PCL) were prepared via ring-opening polymerization, in which the two different moieties were linked via a disulfide bond with reduction responsiveness. After cross-linking by the photodegradable o-nitrobenzyl linkage, the amphiphilic chains could self-assemble into microspheres, branched cylindrical micelles and vesicles, which were responsive to the reduction agent dl-dithiothreitol and UV light irradiation through different mechanisms.

A controllable etching supramolecular hydrogel based on metal ions

We report an interesting gel-etching system in which a gel can be etched with corresponding etching rates and color changes when different types of etching molecules are added to the gel. This gel system may have wide potential application in molecular recognition, pre-packaged, as well as other functional materials.

Harnessing complexity in molecular self-assembly using computer simulations

In molecular self-assembly, hundreds of thousands of freely-diffusing molecules associate to form ordered and functional architectures in the absence of an actuator. This intriguing phenomenon plays a critical role in biology and has become a powerful tool for the fabrication of advanced nanomaterials. Due to the limited spatial and temporal resolutions of current experimental techniques, computer simulations offer a complementary strategy to explore self-assembly with atomic resolution. Here, we review recent computational studies focusing on both thermodynamic and kinetic aspects. As we shall see, thermodynamic approaches based on modeling and statistical mechanics offer initial guidelines to design nanostructures with modest computational effort. Computationally more intensive analyses based on molecular dynamics simulations and kinetic network models (KNMs) reach beyond it, opening the door to the rational design of self-assembly pathways. Current limitations of these methodologies are discussed. We anticipate that the synergistic use of thermodynamic and kinetic analyses based on computer simulations will provide an important contribution to the de novo design of self-assembly.

In-Situ GISAXS Study of Supramolecular Nanofibers having Ultrafast Humidity Sensitivity

Self assembled nanofibers derived from donor-acceptor (D-A) pair of dodecyl methyl viologen (DMV) and potassium salt of coronene tetracarboxylate (CS) is an excellent material for the development of organic electronic devices particularly for ultrafast response to relative humidity (RH). Here we have presented the results of in-situ grazing incidence small angle x-ray scattering (GISAXS) measurements to understand aridity dependent self reorganization of the nanofibers. The instantaneous changes in the organization of the nanofibers was monitored with different equilibrium RH conditions. Additionally formation of nanofibers during drying was studied by GISAXS technique - the results show two distinct stages of structural arrangements, first the formation of a lamellar mesophase and then, the evolution of a distorted hexagonal lattice. The RH dependent GISAXS results revealed a high degree of swelling in the lattice of the micelles and reduction in the distortion of the hexagonal structure with increase in RH. In high RH condition, the nanofibers show elliptical distortion but could not break into lamellar phase as observed during formation through drying. This observed structural deformation gives insight into nanoscopic structural changes of the micelles with change in RH around it and in turn explains ultrafast sensitivity in its conductivity for RH variation.

Entirely oligosaccharide-based supramolecular amphiphiles constructed via host–guest interactions as efficient drug delivery platforms

Entirely oligosaccharide-based supramolecular amphiphiles were constructed via host–guest interactions between ferrocene-terminated acetylated-maltoheptaose (Fc-AcMH) and β-cyclodextrin-terminated four-arm star maltoheptaose (MH₄-β-CD).

Dual photo- and pH-responsive supramolecular nanocarriers based on water-soluble pillar[6]arene and different azobenzene derivatives for intracellular anticancer drug delivery

Two novel types of supramolecular nanocarriers fabricated by the amphiphilic host-guest inclusion complex formed from water-soluble pillar[6]arene (WP6) and azobenzene derivatives G1 or G2 have been developed, in which G1 is structurally similar to G2 but has an extra phenoxy group in its hydrophobic region. Supramolecular micelles can be initially formed by WP6 with G1, which gradually transform into layered structures with liquid-crystalline properties, whereas stable supramolecular vesicles are obtained from WP6 and G2, which exhibit dual photo- and pH-responsiveness. Notably, the resulting WP6⊃G2 vesicles can efficiently encapsulate anticancer drug mitoxantrone (MTZ) to achieve MTZ-loaded vesicles, which maintain good stability in a simulated normal physiological environment, whereas in an acid environment similar to that of tumor cells or with external UV irradiation, the encapsulated drug is promptly released. More importantly, cytotoxicity assay indicates that such vesicles have good biocompatibility and the MTZ-loaded vesicles exhibit comparable anticancer activity to free MTZ, especially with additional UV stimulus, whereas its cytotoxicity for normal cells was remarkably reduced. Flow cytometric analysis further confirms that the cancer cell death caused by MTZ-loaded vesicles is associated with apoptosis. Therefore, the dual pH- and UV-responsive supramolecular vesicles are a potential platform for controlled release and targeted anticancer drug delivery.

Reversible pH-responsive helical nanoribbons formed using camptothecin

The natural antitumor drug camptothecin was found to self-assemble into helical nanoribbons in aqueous solution. The formation and disappearance of the helical nanoribbons can be tuned reversibly through changing the pH value of the solution.