Facile fabrication of self-reporting micellar and vesicular structures based on an etching-ion exchange strategy of photonic composite spheres of poly(ionic liquid).

Micellar and vesicular structures capable of sensing and reporting the chemical environment as well as facilely introducing user-defined functions make a vital contribution to constructing versatile compartmentalized systems. Herein, by combining poly(ionic liquid)-based photonic spheres and an etching-ion exchange strategy we fabricate micellar and vesicular photonic compartments that can not only mimic the structure and function of conventional micelles and vesicles, but also sense and report the chemical environment as well as introducing user-defined functions. Photonic composite spheres composed of a SiO2 template and poly(ionic liquid) are employed to selectively etch outer-shell SiO2 followed by ion exchange and removal of the residual SiO2 to afford micellar photonic compartments (MPCs). The MPCs can selectively absorb solvents from the oil/water mixtures together with sensing and reporting the adsorbed solvents by the self-reporting optical signal associated with the uniform porous structure of photonic spheres. Vesicular photonic compartments (VPCs) are fabricated via selective infiltration and polymerization of ionic liquids followed by etching of the SiO2 template. Subsequent ion exchange introduces desirable functions to the VPCs. Furthermore, we demonstrate that the thickness and the anisotropic functions of VPCs can be facilely modulated. Overall, we anticipate that the micellar and vesicular photonic compartments with self-reporting optical signals and user-defined functions could serve as novel platforms towards multifunctional compartmentalized systems.

Towards photoswitchable quadruple hydrogen bonds via a reversible "photolocking" strategy for photocontrolled self-assembly.

Developing new photoswitchable noncovalent interaction motifs with controllable bonding affinity is crucial for the construction of photoresponsive supramolecular systems and materials. Here we describe a unique "photolocking" strategy for realizing photoswitchable control of quadruple hydrogen-bonding interactions on the basis of modifying the ureidopyrimidinone (UPy) module with an ortho-ester substituted azobenzene unit as the "photo-lock". Upon light irradiation, the obtained Azo-UPy motif is capable of unlocking/locking the partial H-bonding sites of the UPy unit, leading to photoswitching between homo- and heteroquadruple hydrogen-bonded dimers, which has been further applied for the fabrication of novel tunable hydrogen bonded supramolecular systems. This "photolocking" strategy appears to be broadly applicable in the rational design and construction of other H-bonding motifs with sufficiently photoswitchable noncovalent interactions.

Observation of osmotically driven, highly controllable and reconfigurable oil/water phase separation.

Liquid-liquid phase separation has been proven to be a valuable method for producing structured materials and creating chemical systems. Although several strategies have been developed to date, osmotically driven oil/water phase separation has never been achieved owing to the limited solubility of inorganic salts in conventional organic solvents and thus the insufficient osmotic driving force to counterbalance the Laplace pressure associated with the interfacial tension. Herein, we report the discovery that a mixture of 1-alkyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide and LiTf2N can generate sufficient and widely tunable osmotic pressure in oil to realize water transport from the surrounding aqueous phase into the oil phase, triggering spontaneous phase separation. This osmotically driven phase separation could be modulated with unprecedented flexibility, offering unlimited possibilities to facilely access diverse thermodynamically metastable structures using one system. Importantly, this oil system can serve as a general phase separation carrier platform for realizing phase separation of various substances.

A Visible-Light-Induced Dynamic Mechanical Bond as a Linkage for Dynamic Materials.

Exploring dynamic bonds and their applications in fabricating dynamic materials has received great attention. A photoinduced [2]rotaxane-based dynamic mechanical bond (DMB) features visible-light-triggered dynamic bonding behavior that is essentially distinguished from conventional dynamic chemical bonds. In this DMB, a photoisomerizable ortho-fluoroazobenzene unit is introduced as a steric-controllable stopper, the visible-light-induced dynamic wagging movement of which enables the photoregulated threading of the macrocycle. This allows reversible in situ de-/reforming of the mechanical bond without involving dynamic chemical linkage. The DMB-cross-linked polymeric gel shows interesting photoinduced degradation behavior upon visible light irradiation. Benefiting from the distinctive dual dynamic nature of reversible bonding behavior and mechanical interlocked structure, this DMB is expected to serve as a new type of dynamic bond that can be applied in designing dynamic soft materials.

Toward bidirectional photoswitchable colored photochromic molecules with visible light stability.

Photochromic [2]rotaxanes with bidirectional photoswitchability were fabricated, whose colored states exhibit remarkable visible-light and thermal stabilities as revealed by systematically spectroscopic investigations.

Tunable Water-Soluble Supramolecular Polymers by Visible-Light-Regulated Host-Guest Interactions.

The development of artificial self-assembling systems with dynamic photo-regulation features in aqueous solutions has drawn great attention owing to the potential applications in fabricating elaborate biological materials. Here we demonstrate the fabrication of water-soluble cucurbit[8]uril (CB[8])-mediated supramolecular polymers by connecting the fluorinated azobenzene (FAB) containing monomers through host-enhanced heteroternary π-π stacking interactions. Benefiting from the unique visible-light-induced E→Z photoisomerization of the FAB photochromophores, the encapsulation behaviors between the CB[8] macrocycle and the monomers could be regulated upon visible light irradiation, resulting in the depolymerization of such CB[8]-mediated supramolecular polymers.

Microfluidic synthesis of uniform single-crystalline MOF microcubes with a hierarchical porous structure.

Creating hierarchical porosity in MOFs and controlling their size and morphology have emerged as efficient means for achieving significant improvement of MOF properties, and are crucial for facilitating the practical implementation of their various applications. Although important advances in this respect have been made, the realization of a hierarchical pore structure in a single crystalline MOF particle with controlled size and shape is still a challenge, and highly desirable. In this work, based on droplet-based microfluidics in conjunction with evaporative crystallization, an efficient approach to large-scale synthesis of uniform single-crystalline HKUST-1 particles with a hierarchical pore structure is presented. It is found that the MOF crystallization in confined droplets could generate not only monodisperse single-crystalline microcubes with an engraved rich porous texture including bimodal or trimodal pore structures, but also the size and porosity of the resulting cubes as well as the introduced meso- or macropore size could be widely tailored by varying the preparation conditions. Importantly, through the simple addition of an active species into the formed droplets, the functionalization of the resulting pore structured HKUST-1 cubes could be facilely realized, affording a series of high-performance functional nanomaterials.

AIE-doped poly(ionic liquid) photonic spheres: a single sphere-based customizable sensing platform for the discrimination of multi-analytes.

By simultaneously exploiting the unique properties of ionic liquids and aggregation-induced emission (AIE) luminogens, as well as photonic structures, a novel customizable sensing system for multi-analytes was developed based on a single AIE-doped poly(ionic liquid) photonic sphere. It was found that due to the extraordinary multiple intermolecular interactions involved in the ionic liquid units, one single sphere could differentially interact with broader classes of analytes, thus generating response patterns with remarkable diversity. Moreover, the optical properties of both the AIE luminogen and photonic structure integrated in the poly(ionic liquid) sphere provide multidimensional signal channels for transducing the involved recognition process in a complementary manner and the acquisition of abundant and sufficient sensing information could be easily achieved on only one sphere sensor element. More importantly, the sensing performance of our poly(ionic liquid) photonic sphere is designable and customizable through a simple ion-exchange reaction and target-oriented multi-analyte sensing can be conveniently realized using a selective receptor species, such as counterions, showing great flexibility and extendibility. The power of our single sphere-based customizable sensing system was exemplified by the successful on-demand detection and discrimination of four multi-analyte challenge systems: all 20 natural amino acids, nine important phosphate derivatives, ten metal ions and three pairs of enantiomers. To further demonstrate the potential of our spheres for real-life application, 20 amino acids in human urine and their 26 unprecedented complex mixtures were also discriminated between by the single sphere-based array.

Efficient Construction of Well-Defined Multicompartment Porous Systems in a Modular and Chemically Orthogonal Fashion.

A microfluidic assembly approach was developed for efficiently producing hydrogel spheres with reactive multidomains that can be employed as an advantageous platform to create spherical porous networks in a facile manner with well-defined multicompartments and spatiotemporally controlled functions. This strategy allows for not only large scale fabrication of various robust hydrogel microspheres with controlled size and porosity, but also the domains embedded in hydrogel network could be introduced in a modular manner. Additionally, the number of different domains and their ratio could be widely variable on demand. More importantly, the reactive groups distributed in individual domains could be used as anchor sites to further incorporate functional units in an orthogonal fashion, leading to well-defined multicompartment systems. The strategy provides a new and efficient route to construct well-defined functional multicompartment systems with great flexibility and extendibility.

Molecularly imprinted photonic polymers as sensing elements for the creation of cross-reactive sensor arrays.

By combining molecular imprinting and colloidal crystal templating, molecularly imprinted inverse-opal photonic polymers (MIPPs) acting as sensing elements have been exploited to create sensor arrays for the first time. With this new strategy, abundant sensing elements with differential sensing abilities were easily accessible. Because of the unique hierarchical porous structure integrated in each sensing element, high sensitivity and selectivity, fast response and self-reporting (label-free) detection could be simultaneously achieved. All these fascinating features indicate that MIPPs are ideal sensing elements for creating sensor arrays. By integrating the individual sensing elements on a substrate, the formed array chip delivers better portability and high-throughput capability. As a demonstration, six kinds of contaminants were selected as analytes. The detection and discrimination of these analytes and even their mixtures in a wide range of concentrations, particularly trace amounts of analyte against a high background of other components, could be achieved, indicating the powerful capability of MIPPs-based sensor array for sensing. These results suggest that the described strategy opens a new route for sensor array creation and should find important applications in a wide range of areas.

Photonic metal-organic framework composite spheres: a new kind of optical material with self-reporting molecular recognition.

Exploiting metal-organic framework (MOF) materials as novel building blocks to construct superstructures with extended and enhanced functions represents a big challenge. In biological systems, the ordering of many components is not achieved by interaction of the components with each other, but by interaction of each component with the host protein which provides a matrix to support the entire assembly. Inspired by biological systems, in this work, a general strategy for efficient spatial arrangement of MOF materials was developed by using spherical colloidal crystals as host matrices, affording a new class of highly tunable MOF composite spheres with a series of distinctive properties. It was found that the synergetic combination of the unique features of both MOF and photonic colloidal crystal imparted these hierarchically structured spheres intrinsic optical properties, specific molecular recognition with self-reporting signalling, derivatization capability, and anisotropy. More importantly, the unique photonic band-gap structure integrated in these composite spheres provides a more convenient means to manipulate the photophysical and photochemical behaviour of the trapped guest molecules in MOF nanocavities.

Highly sensitive assay for acetylcholinesterase activity and inhibition based on a specifically reactive photonic nanostructure.

Assays for acetylcholinesterase (AChE) with high sensitivity and high selectivity as well as facile manipulation have been urgently required in various fields. In this work, a reaction-based photonic strategy was developed for the efficient assay of AChE activity and inhibition based on the synergetic combination of the specific thiol-maleimide addition reaction with photonic porous structure. It was found that various applications including detection of AChE activity, measurement of the related enzymatic kinetics, and screening of inhibitors could be efficiently implemented using such strategy. Remarkably, the unique photonic nanostructure endows the constructed sensing platform with high sensitivity with a limit of detection (LOD) of 5 mU/mL for AChE activity, high selectivity, and self-reporting signaling. Moreover, the label-free solid film-based sensing approach described here has advantages of facile manipulation and bare-eye readout, compared with conventional liquid-phase methods, exhibiting promising potential in practical application for the AChE assay.

Inverse opal spheres based on polyionic liquids as functional microspheres with tunable optical properties and molecular recognition capabilities.

Based on the combination of the unique features of both polyionic liquids and spherical colloidal crystals, a new class of inverse opaline spheres with a series of distinct properties was fabricated. It was found that such photonic spheres could not only be used as stimuli-responsive photonic microgels, but also serve as multifunctional microspheres that mimic the main characteristics of conventional molecules, including intrinsic optical properties, specific molecular recognition, reactivity and derivatization, and anisotropy.

A new strategy for effective construction of protein stacks by using cucurbit[8]uril as a glue molecule.

Cucurbit[8]uril (CB[8]) is found to induce the aggregation of pristine proteins in aqueous solution. Based on this finding, a new strategy for effective construction of layer-by-layer homo- and hetero-protein stacks was developed, where their bioactivities are preserved.

Reactive photonic film for label-free and selective sensing of cyanide.

Three-dimensional ordered inverse-opal films bearing a reactive trifluoroacetyl group are successfully constructed. Through the specific reaction between cyanide and trifluoroacetyl, the photonic films can selectively detect sub-micromolar levels of cyanide by distinct structural color change. Labeled molecules are not necessary for the sensing mechanism.

Metal-organic frameworks with a three-dimensional ordered macroporous structure: dynamic photonic materials.

Tuning MOFs: When a metal-organic framework (MOF) with an ordered three-dimensional macroporous structure is integrated into a film, the resulting materials have an additional optical element, which can be used as a general and effective signal transducer. This, in combination with the hierarchical pore structure, makes these films interesting dynamic photonic materials with potential applications in sensors.

Facile fabrication of photonic MOF films through stepwise deposition on a colloid crystal substrate.

Based on stepwise deposition of MOF films on a colloid crystal substrate, a strategy for fabricating photonic MOF films was developed. We found that the integration of a photonic structure endows MOF materials with unique optical properties, which can be used as a general and effective transduction scheme for a convenient study of the host-guest chemistry of MOFs.

Confined self-assembly approach to produce ultrathin carbon nanofibers.

A surfactant containing a terminal carbon source moiety was synthesized and used simultaneously as both template molecule and carbon source. On the basis of this special structure-directing agent, an efficient strategy for producing uniform carbon nanowires with diameter below 1 nm was developed using a confined self-assembly approach. Besides the capability of producing ultralong and thin carbon wires inaccessible by the previously reported approaches, the method described here presents many advantages such as the direct use of residue iron complex as catalyst for carbonization and no requirement of conventional tedious infiltration process of carbon source into small channels. Different methods including SEM, TEM, XRD, Raman spectroscopy, and conductivity measurement were employed to characterize the formed ultrathin carbon nanofibers. Additionally, the described strategy is extendable. By designing an appropriate surfactant, it is also possible for the fabrication of the finely structured carbon network and ultrathin graphitic sheets through the construction of the corresponding cubic and lamellar mesostructured templates.