Accelerated Self‐Replication under Non‐Equilibrium,Periodic Energy Delivery

Self‐replication is a remarkable phenomenon in nature that has fascinated scientists for decades. In a self‐replicating system, the original units are attracted to a template, which induce their binding. In equilibrium, the energy required to disassemble the newly assembled copy from the mother template is supplied by thermal energy. The possibility of optimizing self‐replication was explored by controlling the frequency at which energy is supplied to the system. A model system inspired by a class of light‐switchable colloids was considered where light is used to control the interactions. Conditions under which self‐replication can be significantly more effective under non‐equilibrium, cyclic energy delivery than under equilibrium constant energy conditions were identified. Optimal self‐replication does not require constant energy expenditure. Instead, the proper timing at which energy is delivered to the system is an essential controllable parameter to induce high replication rates.     

Spatially Controlled Out‐of‐Equilibrium Host–Guest System under Electrochemical Control

Self‐assembly to create molecular and nanostructures is typically performed at the thermodynamic minimum. To achieve dynamic functionalities, such as adaptability, internal feedback, and self‐replication, there is a growing focus on out‐of‐equilibrium systems. This report presents the dynamic self‐assembly of an artificial host–guest system at an interface, under control by a dissipative electrochemical process using (electrical) energy, resulting in an out‐of‐equilibrium system exhibiting a supramolecular surface gradient. The gradient, its steepness, rate of formation, and complex surface composition after backfilling, as well as the surface compositions after switching between the different states of the system, are assessed and supported by modelling. Our method shows for the first time an artificial surface‐confined out‐of‐equilibrium system. The electrochemical process parameters provide not only control over the system in time, but also in space.     

An “Ingredients” Approach to Functional Self‐Synthesizing Materials: A Metal‐Ion‐Selective,Multi‐Responsive,Self‐Assembled Hydrogel

New methodology for making novel materials is highly desirable. Here, an “ingredients” approach to functional self‐assembled hydrogels was developed. By designing a building block to contain the right ingredients, a multi‐responsive, self‐assembled hydrogel was obtained through a process of template‐induced self‐synthesis in a dynamic combinatorial library. The system can be switched between gel and solution by light, redox reactions, pH, temperature, mechanical energy and sequestration or addition of Mg^II salt.     

Template‐Free Synthesis of Core–Shell TiO2 Microspheres Covered with High‐Energy {116}‐Facet‐Exposed N‐Doped Nanosheets and Enhanced Photocatalytic Activity under Visible Light

Core–shell TiO₂ microspheres possess a unique structure and interesting properties, and therefore, they have received much attention. The high‐energy facets of TiO₂ also are being widely studied for the high photocatalytic activities they are associated with. However, the synthesis of the core–shell structure is difficult to achieve and requires multiple‐steps and/or is expensive. Hydrofluoric acid (HF), which is highly corrosive, is usually used in the controlling high‐energy facet production. Therefore, it is still a significant challenge to develop low‐temperature, template‐free, shape‐controlled, and relative green self‐assembly routes for the formation of core–shell‐structured TiO₂ microspheres with high‐energy facets. Here, we report a template‐ and hydrofluoric acid free solvothermal self‐assembly approach to synthesize core–shell TiO₂ microspheres covered with high‐energy {116}‐facet‐exposed nanosheets, an approach in which 1,4‐butanediamine plays a key role in the formation of nanosheets with exposed {116} facets and the doping of nitrogen in situ. In the structure, nanoparticle aggregates and nanosheets with {116} high‐energy facets exposed act as core and shell, respectively. The photocatalytic activity for degradation of 2,4,6‐tribromophenol and Rhodamine B under visible irradiation and UV/Vis irradiation has been examined, and improved photocatalytic activity under visible light owing to the hierarchical core–shell structure, {116}‐plane‐oriented nanosheets, in situ N doping, and large surface areas has been found.     

Multicolour Self‐Assembled Fluorene Co‐Oligomers: From Molecules to the Solid State via White‐Light‐Emitting Organogels

Five fluorene‐based co‐oligomers have been prepared to study their self‐assembly in a wide range of concentrations, from dilute solutions to the solid state. Subtle changes to the chemical structures, introduced to tune the emission colours over the entire visible range, induce strong differences in aggregation behaviour. Only two of the fluorescent co‐oligomer derivatives self‐assemble to form soluble fibrils from which fluorescent organogels emerge at higher concentrations. In contrast, the other compounds form precipitates. Mixed fluorescent co‐oligomer systems exhibit partial energy transfer, which allows the creation of white‐light‐emitting gels. Finally, a mechanism for the hierarchical self‐assembly of this class of materials is proposed based on experimental results and molecular modelling calculations.     

G‐Quartet‐Based Nanostructure for Mimicking Light‐Harvesting Antenna

Artificial light‐harvesting systems have received great attention for use in photosynthetic and optoelectronic devices. Herein, a system involving G‐quartet‐based hierarchical nanofibers generated from the self‐assembly of guanosine 5′‐monophosphate (GMP) and a two‐step Förster resonance energy transfer (FRET) is presented that mimics natural light‐harvesting antenna. This solid‐state property offers advantages for future device fabrication. The generation of photocurrent under visible light shows it has potential for use as a nanoscale photoelectric device. The work will be beneficial for the development of light‐harvesting systems by the self‐assembly of supramolecular nanostructures.     

Template–polymer commensurability and directed self‐assembly block copolymer lithography

Block copolymer directed self‐assembly (BCP) with chemical epitaxy is a promising lithographic solution for patterning features with critical dimensions under 20 nm. In this work, we study the extent to which lamellae‐forming poly(styrene‐b‐methyl methacrylate) can be directed with chemical contrast patterns when the pitch of the block copolymer is slightly compressed or stretched compared to the equilibrium pitch observed in unpatterned films. Critical dimension small angle X‐ray scattering complemented with SEM analysis was used to quantify the shape and roughness of the line/space features. It was found that the BCP was more lenient to pitch compression than to pitch stretching, tolerating at least 4.9% pitch compression, but only 2.5% pitch stretching before disrupting into dislocation or disclination defects. The more tolerant range of pitch compression is explained by considering the change in free energy with template mismatch, which suggests a larger penalty for pitch stretching than compressing. Additionally, the effect of width mismatch between chemical contrast pattern and BCP is considered for two different pattern transfer techniques. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 595–603     

Light‐Induced Patterned Self‐Assembly Behavior of Isotropic Semiconductor Nanomotors

The self‐assembly of nanomotors is important for the production of materials with functional optical, mechanical and conductive properties. Yet, self‐assembly methods are limited by their slow kinetics and limited scale. Here we report a light‐induced method that yields a large‐scale predefined pattern constructed by self‐organization of nanomotors. The propulsion mechanism has been analyzed to create a matched experimental device, and numerical simulations are used to explore the dynamic energy‐conversion processes. We propose a sizable template fabricating method, which paves the way for new possibilities in surface science.     

A Self‐Delivery Chimeric Peptide for Photodynamic Therapy Amplified Immunotherapy

In this paper, a self‐delivery chimeric peptide PpIX‐PEG₈‐KVPRNQDWL is designed for photodynamic therapy (PDT) amplified immunotherapy against malignant melanoma. After self‐assembly into nanoparticles (designated as PPMA), this self‐delivery system shows high drug loading rate, good dispersion, and stability as well as an excellent capability in producing reactive oxygen species (ROS). After cellular uptake, the ROS generated under light irradiation could induce the apoptosis and/or necrosis of tumor cells, which would subsequently stimulate the anti‐tumor immune response. On the other hand, the melanoma specific antigen (KVPRNQDWL) peptide could also activate the specific cytotoxic T cells for anti‐tumor immunity. Compared to immunotherapy alone, the combined photodynamic immunotherapy exhibits significantly enhanced inhibition of melanoma growth. Both in vitro and in vivo investigations confirm that PDT of PPMA has a positive effect on anti‐tumor immune response. This self‐delivery system demonstrates a great potential of this PDT amplified immunotherapy strategy for advanced or metastatic tumor treatment.     

Self‐ and cross‐associations in two‐component mixed polymer gels

The gel properties of two‐component mixed polymer gels are investigated using a cascade model, which assumes that the gel network is formed via the self‐association of one of the two components and the cross‐association of the two components. The effects of the model parameters, such as the equilibrium constants and the functionalities for cross‐associations and self‐associations, on the composition dependence of the modulus and gel point curves are examined to elucidate the contribution of self‐associations to the gel network. The results show that the characteristics of self‐associations become pronounced when the equilibrium constant or the functionality for self‐associations is comparable to that for cross‐associations. The model is applied to analyze the critical gelling concentration data for xanthan/locust bean gum mixed gels, which shows significant self‐associations at high xanthan compositions. The resulting model curves agree well with the experimental data at all temperatures. The analysis of the temperature dependence of the best‐fit equilibrium constant yields values of enthalpy change that are consistent with previous findings. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 80–91, 2008     

A pH‐Sensitive Lasso‐Based Rotaxane Molecular Switch

The synthesis of a pH‐sensitive two‐station [1]rotaxane molecular switch by self‐entanglement of a non‐interlocked hermaphrodite molecule, containing an anilinium and triazole moieties, is reported. The anilinium was chosen as the best template for the macrocycle benzometaphenylene[25]crown‐8 (BMP25C8) and allowed the self‐entanglement of the molecule. The equilibrium between the hermaphrodite molecule and the pseudo[1]rotaxane was studied by ¹H NMR spectroscopy: the best conditions of self‐entanglement were found in the less polar solvent CD₂Cl₂ and at high dilution. The triazole moiety was then benzylated to afford a benzyltriazolium moiety, which then played a dual role. On one hand, it acts as a bulky gate to trap the BMP25C8, thus to avoid any self‐disentanglement of the molecular architecture. On another hand, it acts as a second molecular station for the macrocycle. At acidic pH, the BMP25C8 resides around the best anilinium molecular station, displaying the lasso [1]rotaxane in a loosened conformation. The deprotonation of the anilinium molecular station triggers the shuttling of the BMP25C8 around the triazolium moiety, therefore tightening the lasso.     

Design and proof of reversible micelle‐to‐vesicle multistimuli‐responsive morphological regulations

Multistimuli‐responsive precise morphological control over self‐assembled polymers is of great importance for applications in nanoscience as drug delivery system. A novel pH, photoresponsive, and cyclodextrin‐responsive block copolymer were developed to investigate the reversible morphological transition from micelles to vesicles. The azobenzene‐containing block copolymer poly(ethylene oxide)‐b‐poly(2‐(diethylamino)ethyl methacrylate‐co‐6‐(4‐phenylazo phenoxy)hexyl methacrylate) [PEO‐b‐P(DEAEMA‐co‐PPHMA)] was synthesized by atom transfer radical polymerization. This system can self‐assemble into vesicles in aqueous solution at pH 8. On adjusting the solution pH to 3, there was a transition from vesicles to micelles. The same behavior, that is, transition from vesicles to micelles was also realizable on addition of β‐cyclodextrin (β‐CD) to the PEO‐b‐P(DEAEMA‐co‐PPHMA) solution at pH 8. Furthermore, after β‐CD was added, alternating irradiation of the solution with UV and visible light can also induce the reversible micelle‐to‐vesicle transition because of the photoinduced trans‐to‐cis isomerization of azobenzene units. The multistimuli‐responsive precise morphological changes were studied by laser light scattering, transmission electron microscopy, and UV–vis spectra. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Energy transfer from fluorene‐based conjugated polyelectrolytes to on‐chain and self‐assembled porphyrin units

A new water soluble fluorene‐based polyelectrolyte containing on‐chain porphyrin units has been synthesized via Suzuki coupling, for use in optoelectronic devices. The material consist of a random copolymer of poly{1,4‐phenylene‐[9,9‐bis(4‐phenoxy butylsulfonate)]fluorene‐2,7‐diyl} (PBS‐PFP) and a 5,15‐diphenylporphyrin (DPP). The energy transfer process between the PBS‐PFP units and the porphyrin has been investigated through steady state and time‐resolved measurements. The copolymer PBS‐PFP‐DPP displays two different emissions one located in the blue region of the spectra, corresponding to the fluorene part and another in the red due to fluorescent DPP units either formed directly or by exciton transfer. However, relatively inefficient energy transfer from the PFP to the on‐chain porphyrin units was observed. We compare this with a system involving an anionic blue light‐emitting donor PBS‐PFP and a anionic red light‐emitting energy acceptor meso‐tetrakisphenylporphyrinsulfonate (TPPS), self‐assembled by electrostatic attraction induced by Ca²⁺. Based on previous studies related to chain aggregation of the anionic copolymer PBS‐PFP, two different solvent media were chosen to further explore the possibilities of the self‐assembled system: dioxane–water and aqueous nonionic surfactant n‐dodecylpentaoxyethylene glycol ether (C₁₂E₅). In contrast, with the on‐chain PBS‐PFP‐DPP system the strong overlap of the 0‐0 emission peak of the PBS‐PFP and the Soret absorption band of the TPPS results in an efficient Förster transfer. This is strongly dependent on the solvent medium used. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Light‐Activated Active Colloid Ribbons

We report a dynamic self‐organization of self‐propelled peanut‐shaped hematite motors from non‐equilibrium driving forces where the propulsion can be triggered by blue light. They result in one‐dimensional, active colloid ribbons with a positive phototactic characteristic. The motion of colloid motors is ascribed to the diffusion‐osmotic flow in a chemical gradient by the photocatalytic decomposition of hydrogen peroxide fuel. We show that self‐propelled peanut‐shaped colloids readily form one‐dimensional, slithering ribbon structures under the out‐of‐equilibrium collisions. This self‐organization intrinsically results from the competition among the osmotically driven motion, the phoretic attraction and the inherent magnetic moments. The giant size number fluctuation in colloid ribbons is observed above a critical point 4.1 % of the surface density of colloid motors. Such phototactic colloid ribbons may provide a model system to understand the emergence of function in biological systems and have potential to construct bioinspired active materials based on different active building blocks.     

From Chemical Gardens to Fuel Cells: Generation of Electrical Potential and Current Across Self‐Assembling Iron Mineral Membranes

We examine the electrochemical gradients that form across chemical garden membranes and investigate how self‐assembling, out‐of‐equilibrium inorganic precipitates—mimicking in some ways those generated in far‐from‐equilibrium natural systems—can generate electrochemical energy. Measurements of electrical potential and current were made across membranes precipitated both by injection and solution interface methods in iron‐sulfide and iron‐hydroxide reaction systems. The battery‐like nature of chemical gardens was demonstrated by linking multiple experiments in series which produced sufficient electrical energy to light an external light‐emitting diode (LED). This work paves the way for determining relevant properties of geological precipitates that may have played a role in hydrothermal redox chemistry at the origin of life, and materials applications that utilize the electrochemical properties of self‐organizing chemical systems.     

Metal‐Folded Single‐Chain Nanoparticle: Nanoclusters and Self‐Assembled Reduction‐Responsive Sub‐5‐nm Discrete Subdomains

Easy access to discrete nanoclusters in metal‐folded single‐chain nanoparticles (metal‐SCNPs) and independent ultrafine sudomains in the assemblies via coordination‐driven self‐assembly of hydrophilic copolymer containing 9% imidazole groups is reported herein. ¹H NMR, dynamic light scattering, and NMR diffusion‐ordered spectroscopy results demonstrate self‐assembly into metal‐SCNPs (>70% imidazole‐units folded) by neutralization in the presence of Cu(II) in water to pH 4.6. Further neutralization induces self‐assembly of metal‐SCNPs (pH 4.6–5.0) and shrinkage (pH 5.0–5.6), with concurrent restraining residual imidazole motifs and hydrophilic segment, which organized into constant nanoparticles over pH 5.6–7.5. Atomic force microscopy results evidence discrete 1.2 nm nanoclusters and sub‐5‐nm subdomains in metal‐SCNP and assembled nanoparticle. Reduction of metal center using sodium ascorbate induces structural rearrangement to one order lower than the precursor. Enzyme mimic catalysis required media‐tunable discrete ultrafine interiors in metal‐SCNPs and assemblies have hence been achieved.     

A Rapidly Self‐Healing Supramolecular Polymer Hydrogel with Photostimulated Room‐Temperature Phosphorescence Responsiveness

Development of self‐healing and photostimulated luminescent supramolecular polymeric materials is important for artificial soft materials. A supramolecular polymeric hydrogel is reported based on the host–guest recognition between a β‐cyclodextrin (β‐CD) host polymer (poly‐β‐CD) and an α‐bromonaphthalene (α‐BrNp) polymer (poly‐BrNp) without any additional gelator, which can self‐heal within only about one minute under ambient atmosphere without any additive. This supramolecular polymer system can be excited to engender room‐temperature phosphorescence (RTP) signals based on the fact that the inclusion of β‐CD macrocycle with α‐BrNp moiety is able to induce RTP emission (CD‐RTP). The RTP signal can be adjusted reversibly by competitive complexation of β‐CD with azobenzene moiety under specific irradiation by introducing another azobenzene guest polymer (poly‐Azo).     

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.     

Effects of Alkyl Chain Length and Hydrogen Bonds on the Cooperative Self‐Assembly of 2‐Thienyl‐Type Diarylethenes at a Liquid/Highly Oriented Pyrolytic Graphite (HOPG) Interface

An appropriate understanding of the process of self‐assembly is of critical importance to tailor nanostructured order on 2D surfaces with functional molecules. Photochromic compounds are promising candidates for building blocks of advanced photoresponsive surfaces. To investigate the relationship between molecular structure and the mechanism of ordering formation, 2‐thienyl‐type diarylethenes with various lengths of alkyl side chains linked through an amide or ester group were synthesized. Their self‐assemblies at a liquid/solid interface were investigated by scanning tunneling microscopy (STM). The concentration dependence of the surface coverage was analyzed by using a cooperative model for a 2D surface based on two characteristic parameters: the nucleation equilibrium constant (K_n) and the elongation equilibrium constant (K_e). The following conclusions can be drawn. 1) The concentration at which a stable 2D molecular ordering is observed by STM exponentially decreases with increasing length of the alkyl chain. 2) Compounds bearing amide groups have higher degrees of cooperativity in self‐assembly on 2D surfaces (i.e., σ, which is defined as K_n/K_e) than compounds with ester groups. 3) The self‐assembly process of the open‐ring isomer of an ester derivative is close to isodesmic, whereas that of the closed‐ring isomer is cooperative because of the difference in equilibrium constants for the nucleation step (i.e., K_n) between the two isomers.     

Efficient one‐pot synthesis of water‐compatible and photoresponsive molecularly imprinted polymer nanoparticles by facile RAFT precipitation polymerization

A facile, general, and highly efficient one‐pot approach to obtain azobenzene (azo)‐containing molecularly imprinted polymer (MIP) nanoparticles with photoresponsive template binding and release properties in aqueous media is described, which involves the combined use of hydrophilic macromolecular chain transfer agent‐mediated reversible addition‐fragmentation chain transfer precipitation polymerization and easily available water‐insoluble azo functional monomers. The resulting azo‐containing MIPs were characterized with dynamic laser scattering (DLS), SEM, FTIR, static contact angle and water dispersion studies, and equilibrium binding experiments. They have proven to be nanoparticles (their diameters being around 104–397 nm, as determined by DLS in methanol) with surface‐grafted hydrophilic polymer brushes and exhibit excellent pure water‐compatible template binding properties. Moreover, obvious photoregulated template binding behaviors were observed for such azo‐containing MIP nanoparticles, which led to their largely accelerated template release in the aqueous media under the UV light irradiation. Furthermore, the general applicability of the strategy was also demonstrated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1941–1952