Design of a Hypersensitive pH-Sensory System Created by a Combination of Charge Neutralization and Aggregation-Induced Emission (AIE).

In our bodies, a slight pH change causes remarkable activation or serious damage in the biological processes and continuously keeps biological homeostasis. Detection of such a slight pH change has been a constant demand in searching for unusual biological events. In this paper, we demonstrate a novel pH sensory system that has been achieved through a combination of charge neutralization by a slight pH change with aggregation-induced emission (AIE). We selected a cyano-functionalized oligo(phenylene-vinylene) (cyanoOPV) backbone for AIE and introduced ammonium-tethered boronic acid groups as a pH-dependent function. The self-assembling of these dyes (OPV-Cn) was readily achieved by pH-dependent charge neutralization at the neutral pH region. This sensory system showed unusually sensitive pH responsiveness in a narrow pH range. Moreover, this pH change was observed in a biologically important neutral pH region. We therefore believe that this system is broadly applicable to detect the slight pH change occurring in the biological events.

A Chiral Recognition System Orchestrated by Self-Assembly: Molecular Chirality, Self-Assembly Morphology, and Fluorescence Response.

The newly developed oligophenylenevinylene (OPV)-based fluorescent (FL) chiral chemosensor (OPV-Me) for the representative enantiomeric guest, 1,2-cyclohexanedicarboxylic acid (1,2-CHDA: RR- and SS-form) showed the high chiral discrimination ability, resulting in the different aggregation modes of OPV-Me self-assembly: RR-CHDA directed the fibrous supramolecular aggregate, whereas SS-CHDA directed the finite aggregate. The consequent FL intensity toward RR-CHDA was up to 30 times larger than that toward SS-CHDA. Accordingly, highly enantioselective recognition was achieved. Application to the chirality sensing was also possible: OPV-Me exhibited a linear relationship between the FL intensity and the enantiomeric excess through the morphological development of stereocomplex aggregates. These results clearly show that the chiral recognition ability is manifested by the amplification cascade of the chirality difference through self-assembly.

Cohelical Crossover Network by Supramolecular Polymerization of a 4,6-Acetalized ß-1,3-Glucan Macromer.

Natural polysaccharides represent a renewable resource whose effective utilization is of increasing importance. Chemical modification is a powerful tool to transform them into processable materials but usually sacrifices the original structures and properties of value. Here we introduce a chemical modification of Curdlan, a ß-1,3-glucan, via 4,6-acetalization. This modification has successfully combined a helix-forming ability of Curdlan with new solubility in organic media. Furthermore, it has operationalized efficient cohelical crossovers (CCs) among the helices to demonstrate the formation of an extensive supramolecular network that goes well beyond the nanoscopic regime, allowing for preparation of flexible self-supporting films with macroscopic dimensions. This protocol, which is now viewed as supramolecular polymerization of a helical polysaccharide macromer, can add a new dimension to "polysaccharide nanotechnology", opening a door for the creation of unconventional polymer materials based on the cohelical crossover network (CCN).

Adaptive Self-Assembly Behavior Restrained by Supramolecular Crystallization and Molecular Recognition.

The control over supramolecular interactions and obtaining information beyond the molecular scale is an extended challenge. The intriguing self-assembly of a perylene-3,4,9,10-tetracarboxylic acid diimide (PDI)-based novel bolaamphiphilic probe is experienced within an artificial environment that is restrained by using supramolecular crystallization and molecular recognition. The bolaamphiphile with a hydrophilic [18]-azacrown ether ring produced nanoaggregates due to differing solubilities in organic and aqueous media. A structural evolution was observed in the presence of alkali metal ions as guests. The metal complexes form a pseudo-cationic structure, which is further involved in an ionic self-assembly with biomolecules, thus resulting new spectroscopic information on the dye self-assembly. The overarching aim of this study is to emphasize the importance of the concept of supramolecular adaptability, which has been used to establish an environment-friendly behavior based on noncovalent forces, thus leading to the evolution of new assembly structures and photophysical properties.

Data in support of preparation and functionalization of a clickable polycarbonate monolith.

This data article provides supplementary figures to the research article entitled, "Phase separation approach to a reactive polycarbonate monolith for "click" modifications" (Xin et al., Polymer, 2015, doi:10.1016/j.polymer.2015.04.008). Here, the nitrogen adsorption/desorption isotherms of the prepared porous polycarbonate monolith are shown to classify its inner structure and calculate the specific surface area. The monoliths were modified by using the thiol-ene click chemistry and the olefin metathesis, which was examined by contact angle measurements, FT-IR, solid state 13C NMR spectroscopy as well as thermogravimetric analysis.

Emergent Molecular Recognition through Self-Assembly: Unexpected Selectivity for Hyaluronic Acid among Glycosaminoglycans.

Oligophenylenevinylene (OPV)-based fluorescent (FL) chemosensors exhibiting linear FL responses toward polyanions were designed. Their application to FL sensing of glycosaminoglycans (heparin: HEP, chondroitin 4-sulfate: ChS, and hyaluronic acid: HA) revealed that the charge density encoded as the unit structure directs the mode of OPV self-assembly: H-type aggregate for HEP with 16-times FL increase and J-type aggregate for HA with 93-times FL increase, thus unexpectedly achieving the preferential selectivity for HA in contrast to the conventional HEP selective systems. We have found that the integral magnitude of three factors consisting of binding mechanism, self-assembly, and FL response can amplify the structural information on the target input into the characteristic FL output. This emergent property has been used for a novel molecular recognition system that realizes unconventional FL sensing of HA, potentially applicable to the clinical diagnosis of cancer-related diseases.

Amplified fluorescence emission of bolaamphiphilic perylene-azacrown ether derivatives directed towards molecular recognition events.

Long-term creative approaches have been considered in the design of molecular probes to overcome the quenching effect of important dyes in an aqueous medium. Using the rational donor-acceptor based design principle, we demonstrate herein the different fluorescence states of a non-conjugated symmetrical perylene-azacrown ether system in a solution, from the molecular to the aggregated states. The ethylene-spacer is exceptionally capable of fluorescence enhancement, even in the aggregated state (organic nanoparticle, ONPs, 44 nm), overcoming the quenching effect on changing the solvent from tetrahydrofuran to water. The ONPs with crown ether receptors at the surface show colloidal stability in an aqueous solution. Furthermore, an improved fluorescent state is developed via ONPs-polymer (protamine, Pro) hybridization. Supramolecular interactions between the crown ring and the guanidinium group in Pro play an important role in the ONPs-Pro hybrid formation. The decorated fluorescent hybrid state is finally used as a nano-probe for sensing heparin via the turn-OFF mechanism. The decoration method is further generalized by recognition of the nucleotides. Herein, we detail the bottom-up approach to the molecular design and development of the different fluorescent states of a useful probe. Most excitingly, this new approach is very general and adaptive to facile detection.

Luminescent multi-terpyridine ligands: towards 2D polymer formation in solution.

The investigated multiterpyridine chromophores form a 2D network upon metal ion complexation that causes profound changes to their photophysical properties; the experimental results are complemented by modeling of the electronic properties of isolated monomers as well as the structure of the polymeric network.

Synthesis of two-dimensional analogues of copolymers by site-to-site transmetalation of organometallic monolayer sheets.

Monolayer sheets have gained attention due to the unique properties derived from their two-dimensional structure. One of the key challenges in sheet modification/synthesis is to exchange integral parts while keeping them intact. We describe site-to-site transmetalation of Zn(2+) in the netpoints of cm(2)-sized, metal-organic sheets by Fe(2+), Co(2+), and Pb(2+). This novel transformation was done both randomly and at predetermined patterns defined by photolithography to create monolayer sheets composed of different netpoints. All transmetalated sheets are mechanically strong enough to be spanned over 20 × 20 µm(2) sized holes. Density functional theory calculations provide both a model for the molecular structure of an Fe(2+)-based sheet and first insights into how transmetalation proceeds. Such transmetalated sheets with random and patterned netpoints can be considered as two-dimensional analogues of linear copolymers. Their nanoscale synthesis presents an advance in monolayer/polymer chemistry with applications in fields such as surface coating, molecular electronics, device fabrication, imaging, and sensing.

Room Temperature Synthesis of a Covalent Monolayer Sheet at Air/Water Interface Using a Shape-Persistent Photoreactive Amphiphilic Monomer.

The shape-persistent monomer 3 with its three 1,8-diazaanthracene (DAA) units is spread and compressed at the air/water interface and the layer then converted into a 1.5 nm thick covalent monolayer sheet by photoirradiation under ambient conditions. The sheet obtained under these extremely mild conditions is mechanically stable to carry its own weight when spanned over TEM grids. While its molecular structure cannot be given yet with certainty, it is likely to be the result of [4 + 4]-cycloaddition dimerizations between the DAA units of neighboring monomers. Evidence is based on the wavelength of the monomer fluorescence emission, the kinetics of this emission's intensity decay with irradiation time, and the mechanical sheet stability that suggests a surpassing of percolation threshold. Finally, the thermal stability of the sheet is investigated.

Synthesis of a covalent monolayer sheet by photochemical anthracene dimerization at the air/water interface and its mechanical characterization by AFM indentation.

Covalent monolayer sheets in 2 hours: spreading of threefold anthracene-equipped shape-persistent and amphiphilic monomers at the air/water interface followed by a short photochemical treatment provides access to infinitely sized, strictly monolayered, covalent sheets with in-plane elastic modulus in the range of 19 N/m.

Square-micrometer-sized, free-standing organometallic sheets and their square-centimeter-sized multilayers on solid substrates.

Oligofunctional terpyridine-based monomers are spread at an air/water interface, where they are connected with transition metal salts such as Fe(II) into mechanically coherent monolayer sheets of macroscopic dimension. The conversions of these processes are determined by XPS for several monomer/metal ion combinations. The sheets are transferred onto TEM grids, the 20 × 20 square micrometer sized holes of which can be spanned. AFM indentation experiments provide in-plane elastic moduli which are compared with naturally occurring sheets such as graphene. The new organometallic sheets are also used to create multilayer assemblies on square centimeter length scales on solid substrates. Finally some directions are provided where this research can lead to in future and where its application potential lies.

A two-dimensional polymer from the anthracene dimer and triptycene motifs.

A two-dimensional polymer (2DP) based on the dimerization of anthraceno groups arranged in a triptycene motif is reported. A photoinduced polymerization is performed in the crystalline state and gives a lamellar 2DP via a crystal-to-crystal (but not single-crystal to single-crystal) transformation. Solvent-induced exfoliation provides monolayer sheets of the 2DP. The 2DP is considered to be a tiling, a mathematical approach that facilitates structural elucidation.

Synthesis of shape-persistent macrocycles with three 1,8-diazaanthracene units and their packing in the single crystal.

The synthesis of four shape-persistent macrocycles with three 1,8-diazaanthracene units each is reported (2,3 a-3 c). For two of them single crystals could be obtained and the structures in the crystal be solved. The structures reveal that macrocycle 2 self-dimerizes in the solid state; surprisingly it also forms a stable dimer in solution. The reason for this is seen in unusually efficient dispersion interactions as a consequence of the large contact areas in the dimer. All macrocycles are assessed as to their applicability in lateral polymerizations in the single crystal as well as in solution.

Approaching two-dimensional polymers with macroscopic sizes.

We describe the challenges involved with extending the limited lateral size of two-dimensional polymers (2DPs). An amphiphilic monomer with three-fold symmetry is chosen to form an ideally tessellated monolayer at the air/water interface. Anthracene [4+4] photo-dimerization is chosen as the growth reaction. Formation of covalent net-points upon anthracene dimerization has an influence on the mechanical coherence of the resulting sheets which could be investigated qualitatively and quantitatively by means of AFM nano-indentation.

Solid-state photopolymerization of a shape-persistent macrocycle with two 1,8-diazaanthracene units in a single crystal.

A macrocyclic monomer with two opposing 1,8-diazaanthracene units is polymerized in a single crystal by a photochemically induced [4 + 4] cycloaddition reaction between neighboring monomers in which the anthracene units are stacked face-to-face at the critical Schmidt distance. The severe structural changes associated with this are minimized by the monomer design, wherein the linkers between the two opposing photoreactive 1,8-diazaanthracene units are connected to the 4 and 5 positions of the latter, whose spatial positioning is changed the least during dimerization. This helps to keep the monomer's overall shape basically unchanged during the polymerization. The resulting new rigid-rod polymer is soluble in its protonated form, and after counterion exchange with a surfactant, it can be depolymerized back into monomer upon relatively mild thermal treatment (120 °C) in an organic solvent.

A two-dimensional polymer prepared by organic synthesis.

Synthetic polymers are widely used materials, as attested by a production of more than 200 millions of tons per year, and are typically composed of linear repeat units. They may also be branched or irregularly crosslinked. Here, we introduce a two-dimensional polymer with internal periodicity composed of areal repeat units. This is an extension of Staudinger's polymerization concept (to form macromolecules by covalently linking repeat units together), but in two dimensions. A well-known example of such a two-dimensional polymer is graphene, but its thermolytic synthesis precludes molecular design on demand. Here, we have rationally synthesized an ordered, non-equilibrium two-dimensional polymer far beyond molecular dimensions. The procedure includes the crystallization of a specifically designed photoreactive monomer into a layered structure, a photo-polymerization step within the crystal and a solvent-induced delamination step that isolates individual two-dimensional polymers as free-standing, monolayered molecular sheets.

Macrocyclic amphiphiles with 1,8-anthrylene fluorophores: synthesis and attempts toward two-dimensional organization.

New macrocyclic amphiphiles with two or three integrated 1,8-anthrylenes have been synthesized by an iterative Sonogashira cross-coupling protocol. The final cyclization has been conducted with 80% yield under cuprous-free dilution conditions. Formation of a monolayer at the air/water interface has also been demonstrated. These results open the intriguing possibility to construct large 2D supramolecular/macromolecular systems for which unique photophysical and -chemical properties are expected.

Photoisomerization-induced tunable LCST phase separation of azobenzene-containing polymers in an ionic liquid.

4-phenylazophenyl methacrylate (AzoMA) and benzyl methacrylate (BnMA) were copolymerized to produce multistimuli-responsive polymers (P(AzoMA-r-BnMA)s) in a hydrophobic ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide ([C2mim][NTf2]), as the solvent. P(AzoMA-r-BnMA)s with a maximum of ca. 4 mol % AzoMA were soluble in [C2mim][NTf2] at low temperatures, and they underwent lower critical solution temperature (LCST) phase separation with an increase in temperature. Under UV and visible light irradiation, P(AzoMA-r-BnMA)s underwent reversible photochromism of trans-to-cis and cis-to-trans isomerization, respectively. The LCST temperature differences between trans- and cis-form polymers in the IL were as large as 22 degrees C. Reversible photoinduced phase separation of the polymers was achieved at a certain temperature; at this temperature, the cis-form polymers were soluble in the IL, but the trans-form polymers were not.