Cascading responses of stimuli-responsive materials

Responsiveness to stimuli is important in daily life: natural biological activity is governed by continuous stimulus responsiveness. The design of stimuli-responsive materials is required for the development of advanced sensing systems. Although fully controlled stimuli-responsive systems have been constructed in nature, artificial systems remain a challenge. Conventional stimuli-responsive materials show direct responsiveness to an applied stimulus (Stimulus 1), with structural changes in their molecules and organized states. This feature article focuses on cascading responses as a new concept for integrating stimuli-responsive material design. In cascading responses, an original stimulus (Stimulus 1) is converted into other stimuli (Stimulus 2, 3, …, N) through successive conversions. Stimulus N provides the eventual output response. Integration of multiple stimuli-responsive materials is required to achieve cascading responses. Although cascade, domino, and tandem chemical reactions have been reported at the molecular level, they are not used for materials with higher organized structures. In this article, we introduce functional carriers and sensors based on cascading responses as model cases. The concept of cascading responses enables the achievement of transscale responsivity and sensitivity, which are not directly induced by the original stimulus or its responsive material, for the development of advanced dynamic functional materials.

Enhanced sensitivity in Staphylococcus aureus detection: Unveiling the impact of lipid composition on the performance of carboxyfluorescein (CF)-Loaded liposome-based assay

Liposomes have emerged as versatile nanocarriers, finding applications not only in drug delivery but also in pathogen detection and diagnostics. This study aimed to enhance the sensitivity of liposomes to Staphylococcus aureus by investigating the impact of lipid composition on liposomes loaded with 5(6)-carboxyfluorescein (CF). Liposomes were fabricated using various concentrations of cholesterol (10-40 mol%) combined with saturated phospholipids. Dynamic light scattering results revealed that higher cholesterol concentrations led to reduced liposome size, CF release (%), and entrapment efficiency (%). Liposome sensitivity towards S. aureus was evaluated by using CF-loaded liposomes with and without aptamer insertion. Liposomes with a higher cholesterol content (40 mol%) exhibited a strong ability to detect low bacterial concentrations down to 5 × 102 CFU/mL without relying solely on specific receptor-ligand recognition. However, functionalizing the liposome with an aptamer further improved the specificity and sensitivity of S. aureus detection at even lower concentrations, down to 80 CFU/mL, in the wide range of 80-107 CFU/mL. This study highlights the potential for optimizing the lipid composition of liposomes to improve their sensitivity for pathogen detection, particularly when combined with aptamer-based strategies.

Thermochromic Behavior of Polydiacetylene Nanomaterials Driven by Charged Peptide Amphiphiles

The tunability of chromatic phases adapted by chromogenic polymers such as polydiacetylene (PDA) is key to their utility for robust sensing applications. Here, we investigated the influence of charged peptide interactions on the structure-dependent thermochromicity of amphiphilic PDAs. Solid-state NMR and circular dichroism analyses show that our oppositely charged peptide-PDA samples have distinct degrees of structural order, with the coassembled sample being in between the β-sheet-like positive peptide-PDA and the relatively disordered negative peptide-PDA. All solutions exhibit thermochromicity between 20 and 80 °C, whereby the hysteresis of the blue, planar phase is much larger than that of the red, twisted phase. Resonance Raman spectroscopy of films demonstrates that only coassemblies with electrostatic complementarity stabilize coexisting blue and red PDA phases. This work reveals the nature of the structural changes responsible for the thermally responsive chromatic transitions of biomolecule-functionalized polymeric materials and how this process can be directed by sequence-dictated electrostatic interactions.

Biomimetic Sequence-Templating Approach toward a Multiscale Modulation of Chromogenic Polymer Properties

Precision control via molecular structure over adaptive conjugated polymer properties in aqueous environments is critical for realizing their biomedical applications. Here, we unravel the dependence of amphiphilic peptide-polydiacetylene (PDA) conjugate properties on the characteristic steric and hydrophobic contributions within peptide segments that serve as a biomimetic template for diacetylene polymerization in water. We investigated the functional impacts of molecular volume and polarity changes brought by dipeptide substitution domains on the following peptide-PDA material properties at multiple length scales: supramolecular assembly behavior, chain conformation-dependent photophysical properties, cell-material interfacing, and for the first time, bulk electrical properties of their films processed in water. A library of peptide-PDAs with systematically varied sequences show that the contributions of steric effects predominantly influence the electronic structure and resulting trends in photophysical properties, while the interplay between size and hydrophobicity of individual residues becomes more significant for higher-order assemblies affecting bulk properties. This work demonstrates sequence-tunable molecular volume and polarity as synthetic handles to rationally modulate PDA material properties across length scales, providing insights into the programmability of biomimetic conjugated polymers with adaptive functionalities.

A highly sensitive friction-imaging device based on cascading stimuli responsiveness

Imaging and measurement of friction forces are required in a variety of fields. If the friction forces originating from the motions of professionals are quantitatively analyzed, the data can be applied to a motion-copying system by a robot. However, weak friction forces have not been visualized and quantified using conventional sensing materials and devices because of their low sensitivity. Here we present a highly sensitive friction-imaging device based on the cascading responses of stimuli-responsive materials, namely polydiacetylene (PDA) and dry liquid (DL). Weak friction forces disrupt the DL, which is composed of liquid droplets surrounded by solid particles. The outflowing liquid under chemical stress changes the color of PDA. The cascading responses enable colorimetric imaging and measurement of weak friction forces in the range of 0.006-0.080 N. Furthermore, the device visualizes the force distribution of handwriting in calligraphy depending on the individual characteristics of an expert, a practician, and a beginner. A high-sensitivity friction-imaging device can be used to understand various motions.

Amide-Assisted Polymerization of 1,3-Butadiyne Containing Thiolate Ligands on Small Gold Nanoparticles

Incorporation of directing amide groups has been shown to facilitate the topochemical polymerization of 1,3-butadiyne (diacetylene) groups in noncrystalline phases such as gels, amorphous solids, and liquid crystals. It remains challenging to polymerize 1,3-butadiyne-containing alkylthiolate ligands within their self-assembled monolayers on gold nanoparticles (AuNPs), which enhances their stability and adds new optical and electronic properties. Especially smaller AuNPs of sizes below 5 nm in diameter have been reported to display sluggish photopolymerization and are susceptible to photodegradation under UV irradiation. To probe the effectiveness of the amide-directed photopolymerization of 1,3-butadiyne ligands, small AuNPs in the 2-4 nm range were synthesized that contain alkylthiolate ligands with and without amide and 1,3-butadiyne groups. Their photopolymerization and photostability were studied by transmission electron microscopy (TEM), UV-vis spectroscopy, and Raman spectroscopy. AuNP with amide-free 1,3-butadiyne ligands templated the polymerization of the 1,3-butadiyne ligands but fused to large and insoluble particles during the polymerization process. AuNPs with ligands containing both 1,3-butadiyne and amide groups polymerized significantly faster, which slowed down photodegradation. A UV irradiation (254 nm and 176 W/m²) for 5-10 min was found to be optimal for the AuNPs with directing amide groups studied here, although their average core sizes grew from 3.8 to 4.0 nm in diameter and about 20% of the attached 1,3-butadiyne ligands remained unreacted after 10 minutes of irradiation. About 75% of the attached 1,3-butadiyne ligands were already polymerized during the first 5 min of UV irradiation. This decrease in reactivity is reasoned with a fast polymerization of ligands attached to facet sites and slower polymerization rates for ligands attached to edge and corner sites. Unexpectedly, photopolymerization occurred only in the presence of solvent, whereas no polydiacetylene was generated when dry powders of any of the diacetylene-containing gold nanoparticles were irradiated.

Recent progress in polydiacetylene mechanochromism

Polydiacetylenes (PDAs) are a family of mechanochromic polymers that change color from blue to red and emit fluorescence when exposed to external stimuli, making them extremely popular materials in biosensing. Although several informative reviews on PDA biosensing have been reported in the last few years, their mechanochromism, where external forces induce the color transition, has not been reviewed for a long time. This mini review summarizes recent progress in PDA mechanochromism, with a special focus on the quantitative and nanoscopic data that have emerged in recent years.

A Layered Polydiacetylene Containing Hydrogen-Bonding 4,4'-Bipyridyl Guests: Reversible Color Changes with a Wide-Range Temperature Response

Layered organic polymers have intercalation capabilities and dynamic properties. In classical intercalation chemistry, the interlayer guests are intercalated in the host layers via electrostatic interaction. The present work shows the organic layered materials with the host-guest interlayer interaction via hydrogen bond. Polydiacetylene (PDA) exhibits color changes from blue to red with the application of external stimuli, such as thermal and mechanical stresses. Here we report on a layered PDA containing 4,4'-bipyridyl in the interlayer space as a hydrogen-bonding guest. Whereas the layered PDA without interlayer guest shows the color transition at 65 °C, gradual color changes with two-stage reversibility are observed in the temperature range of -20-240 °C by the introduction of the hydrogen-bonding guest. The weaker interlayer interaction via the hydrogen bond promotes the dynamic motion directing the thermoresponsive color changes in a wide temperature range.

Rational Design of Diphenyldiacetylene-Based Fluorescent Materials Enabling a 365-nm Light-Initiated Topochemical Polymerization

Photopolymerization of diacetylenes usually requires stringent reaction conditions like high energy irradiation of 254-nm light or even γ-rays, which are generally harmful to the human body and thus mild conditions with lower energy irradiation are required. In this study, different diphenyldiacetylene (DPDA) derivatives were rationally designed followed by the investigation of their photopolymerization behavior. It was found that the para-substituted amino groups could render the absorption band of DPDA bathochromically shifted, ensuring a 365-nm light wavelength coverage. On this basis, an organogel system was constructed by chemically modifying cholesteryl and lipoic acid onto the DPDA moiety in aromatic solvents. Such uniform self-assemblies further facilitated to a rather high degree of polymerization by 365-nm irradiation. As a kind of fluorescent materials, the whole polymerization process of this system can be visualized by a photoluminescent signal.

Structures and strategies for enhanced sensitivity of polydiacetylene(PDA) based biosensor platforms

Polydiacetylene (PDA) is a versatile polymer that has been studied in numerous fields because of its unique optical properties derived from alternating multiple bonds in the polymer backbone. The conjugated structure in the polymer backbone enables PDA to possess the ability of blue-red colorimetric transition when π-π interactions in the PDA backbone chain are disturbed by the external environment. The chromatic property of PDA disturbed by external stimuli can also emit fluorescence in the red region. Owing to the unique characteristics of PDA, it has been widely studied in facile and label-free sensing applications based on colorimetric or fluorescence signals for several decades. Among the various PDA structures, membrane structures assembled by amphiphilic molecules are widely used as a versatile platform because facile modification of the synthetic membrane provides extensive applications, such as receptor-ligand interactions, resulting in potent biosensors. To use PDA as a sensory material, several methods have been studied to endow the specificity to PDA molecules and to amplify the signal from PDA supramolecules. This is because selective and sensitive detection of target materials is required at an appropriate level corresponding to each material for applicable sensor applications. This review focuses on factors that affect the sensitivity of PDA composites and several strategies to enhance the sensitivity of the PDA sensor to various structures. Owing to these strategies, the PDA sensor system has achieved a higher level of sensitivity and selectivity, enabling it to detect multiple target materials for a full field of application.

Intercalation and flexibility chemistries of soft layered materials

Layered materials, alternate stackings of two or more components, are found in a wide range of scales. Chemists can design and synthesize layered structures containing functional units. The soft-type layered materials exhibit characteristic dynamic functions originating from two-dimensional (2D) anisotropy and structure flexibility. This feature article focuses on "intercalation" and "flexibility" as two new perspectives for designing soft layered materials. Intercalation of guests is a characteristic approach for design of layered structures. Flexibility is an important factor to control the dynamic functions of the layered structures. As a model case, the intercalation-induced tunable stimuli-responsive color-change properties of layered polydiacetylene (PDA) are introduced to study the impact of the intercalation and flexibility on the dynamic functions. Recently, layered materials have drastically expanded the research area from conventional rigid inorganic compounds to new self-assembled nanostructures consisting of organic components, such as polymers, metal-organic frameworks, and covalent-organic frameworks. These new layered architectures have potentials for exhibiting dynamic functions originating from the structure flexibility beyond the static properties originating from classical intercalation and host-guest chemistries. Therefore, intercalation and flexibility chemistries of soft layered materials are regarded as new perspectives for design of advanced dynamic functional materials.

Self-Assembly Behavior of Diacetylenic Acid Molecules upon Vapor Deposition: Odd-Even Effect on the Film Morphology

A series of linear carboxylic acids containing diacetylenic units at different positions along the chain (C₁₂ H₂₅ (C≡C)₂ (CH₂ )_n COOH, n=7-11) were vacuum-deposited on clean silica substrates. The morphologies of the initial films after UV irradiation were studied. A clear odd-even effect on the morphology of the initial film was observed in that, depending on the spacer length between the diacetylenic unit and carboxyl head group, rings or dendrites of acid dimer layers were obtained. A molecular dynamic simulation of the aggregation process suggests that two competing intermolecular interactions and thus aggregation directions are involved and modulated by the odd or even carbon chain length. Further modulation of the interaction by substitution of a phenyl group at the terminus of the chain or by changing the carboxyl head group to an amidobenzoic acid head group led to a similar odd-even effect but with different dimensions or trends, which can be rationalized similarly. These results give the opportunity to create aligned conjugated polymer chains of different dimensions through self-assembly for applications in molecular/organic electronics.

Solid-State Low-Temperature Thermoresponsive and Reversible Color Changes of Conjugated Polymer in Layered Structure: Beyond Infrared Thermography

Emergence of thermoresponsive and reversible color changes at low temperature is a challenging target. In general, it is not easy to induce sufficient dynamic motion of rigid molecules including chromophore at a lower temperature. The present work shows unusually low-temperature color-change properties originating from the dynamic motion of rigid conjugated polymer in solid state. The layered composites of polydiacetylene (PDA) and guest l-arginine (L-Arg) (PDA-(L-Arg)) exhibit temperature-responsive gradual color changes with reversibility in the range of 123-333 K in solid crystalline state. The dynamic properties are induced by gradual and reversible distortion of the π-conjugated main chain in response to temperature. The tuned flexibility of the layered structure facilitates motion of the rigid π-conjugated molecule at low temperature. The PDA-(L-Arg)-coated substrates are applied to visualization and quantification of 2D and 3D temperature distributions generated by cooling with liquid nitrogen. These thermographic devices afford to image lower temperature range than typical infrared thermography. The present work indicates potentials of layered architectures with tunable flexibility for emergence of dynamic properties.

Co-solvent polarity tuned thermochromic nanotubes of cyclic dipeptide-polydiacetylene supramolecular system

The cooperative non-covalent interactions arising from structurally integrated multiple molecules have emerged as a powerful tool for the creation of functional supramolecular structures. Herein, we constructed cyclic dipeptide (CDP)–polydiacetylene (PDA) conjugate (CDP–DA) by introducing cyclo(l-Phe-l-Lys) to the linear 10,12-pentacosadiynoic acid. Owing to extensive hydrogen bonding characteristics, together with structural chirality of cyclo(l-Phe-l-Lys) and strong π–π stacking diacetylenic template, CDP–DA generated supramolecular nanotubes. The structural visualization using scanning and transmission electron microscopy revealed chloroform/methanol co-solvent polarity tuned morphological transformation of intrinsic lamellar assemblies into nanotubes comprising single-wall and multi-wall structure. The mechanistic understanding by X-ray diffraction patterns confirms bilayer organization in lamellar structure, which forms nanotubes via a gradual lamellar curling-to-scrolling process. The supramolecular CDP–DA nanotubes are transformed into the rigid covalently cross-linked blue-phase polydiacetylene (CDP–PDA) by UV irradiation. Very interestingly, the blue-phase nanotubes display reversible thermochromic changing temperature up to 150 °C with excellent repeatability over a dozen thermal cycles. This work provides an efficient strategy for precise morphological control and aiding the perspective for development in nanostructures for functional devices.

Co-solvent controlled fabrication of thermo-responsive chromogenic nanotubes of a cyclic dipeptide–polydiacetylene supramolecular system.

A Polydiacetylene-Based Colorimetric Sensor as an Active Use-By Date for Plant-Based Milk Alternatives

Existing date marking tools, such as use-by and sell-by dates, fail to inform decision-making throughout food distribution because they do not adapt to storage conditions such as temperature. Polymer-based sensors can be incorporated into food packaging to provide an indication of food quality in real time, which can greatly reduce waste. This work identifies free fatty acid (FFA) as a marker for the quality of plant-based milk and demonstrates the first detection tool for the freshness of almond milk using phospholipid-doped polydiacetylene (PDA) vesicles. The sensor discriminates between triglycerides and FFA by a visible color change and can therefore be used to track fat metabolism during food spoilage. The interaction between FFA and PDA is investigated by electron microscopy and dynamic-light-scattering studies. PDA vesicles are then fabricated in agarose and used to discriminate between fresh and spoiled almond milk. Upon exposure of the PDA/agarose sensor to spoiled almond milk, a visible blue-to-red color change is induced in the film, which is correlated with FFA concentration in the samples. Incorporation of this technology into food packaging can be used to indicate food quality in real time, surpassing the efficacy of current date marking tools to reduce food waste.

The rise of bio-inspired polymer compartments responding to pathology-related signals

Self-organized nano- and microscale polymer compartments such as polymersomes, giant unilamellar vesicles (GUVs), polyion complex vesicles (PICsomes) and layer-by-layer (LbL) capsules have increasing potential in many sensing applications. Besides modifying the physicochemical properties of the corresponding polymer building blocks, the versatility of these compartments can be markedly expanded by biomolecules that endow the nanomaterials with specific molecular and cellular functions. In this review, we focus on polymer-based compartments that preserve their structure, and highlight the key role they play in the field of medical diagnostics: first, the self-assembling abilities that result in preferred architectures are presented for a broad range of polymers. In the following, we describe different strategies for sensing disease-related signals (pH-change, reductive conditions, and presence of ions or biomolecules) by polymer compartments that exhibit stimuli-responsiveness. In particular, we distinguish between the stimulus-sensitivity contributed by the polymer itself or by additional compounds embedded in the compartments in different sensing systems. We then address necessary properties of sensing polymeric compartments, such as the enhancement of their stability and biocompatibility, or the targeting ability, that open up new perspectives for diagnostic applications.

Solid-Phase Radical Polymerization of Halogen-Bond-Based Crystals and Applications to Pre-Shaped Polymer Materials

Liquid vinyl monomers were converted into solid crystals via halogen bonding. They underwent solid-phase radical polymerizations through heating at 40 °C or ultraviolet photo-irradiation (365 nm). The X-ray crystallography analysis showed the high degree of monomer alignment in the crystals. The polymerizations of the solid monomer crystals yielded polymers with high molecular weights and relatively low dispersities because of the high degree of the monomer alignment in the crystal. As a unique application of this system, the crystalized monomers were assembled to pre-determined structures, followed by solid-phase polymerization, to obtain a two-layer polymer sheet and a three-dimensional house-shaped polymer material. The two-layer sheet contained a unique asymmetric pore structure and exhibited a solvent-responsive shape memory property and may find applications to asymmetric membranes and polymer actuators.

Visualization and Quantification of Microwaves Using Thermoresponsive Color-Change Hydrogel

Visualization and quantification of invisible lights, such as microwaves, are significant for their safe use. In general, a sensitizer material combined with a transistor is used as electronic devices for the measurement. Here, we developed a thermoresponsive color-change hydrogel of poly(N-isopropylacrylamide) (PNIPAAm) cross-linked by a layered organic composite based on polydiacetylene (PDA) for visualization and colorimetric quantification of microwaves. The layered PDA in the PNIPAAm hydrogel showed the temperature-dependent gradual color change with heating. Irradiation of microwaves induced the color change of PDA through heating of water in the hydrogel and subsequent volume shrinkage. The color of the gel was applied to visualize the temperature distribution with increasing irradiation time of microwaves. Moreover, the power of the irradiated microwave was quantified by time to the complete color change of the gel. The results indicate that the stimulus conversion process has potentials for development of a variety of imaging and quantification devices based on the layered PDA.

3D Printing of Polydiacetylene Photocomposite Materials: Two Wavelengths for Two Orthogonal Chemistries

Polydiacetylene (PDA) materials are appealing and gaining increasing research interest due to their outstanding chromatic transition and fluorescence enhancement effects upon exposure to various environmental stimuli. However, despite the photomask method, there are very few reports about the spatial controllable photopolymerization and subsequent 3D printing of PDA until now. Herein, for the first time, we reported the preparation of PDA photocomposite materials based on polyacrylate through the strategy of dual-wavelength polymerization and orthogonal chemistry. First, diacetylene (DA) monomers were homogeneously dispersed in acrylate resin. Then a violet light emitting diode (LED) (or laser diode) was used for the free radical polymerization of polyacrylate. Finally, UV irradiation was utilized to induce the 1,4-topopolymerization of PDA, which could show a successive blue to purple to red color transition in response to the gradient increment of temperature. Interestingly, instead of photomasks, we applied a 3D printing approach directly to this composite material and fabricated some macroscopic stereo patterns, which also illustrated thermochromic properties. This novel kind of functional photocomposite material would demonstrate a huge application prospect in many potential fields, including colorimetric sensing, information encryption, anticounterfeiting, and so on.

A minireview of hydroamination catalysis: alkene and alkyne substrate selective, metal complex design

Organic compounds that contain nitrogen are very important intermediates in pharmaceutical and chemical industry. Hydroamination is the reaction that can form C-N bond with high atom economy. The research progress in metals catalyzed hydroamination of alkenes and alkynes from the perspective of reaction mechanism is categorized and summarized.

Photoinduced Reversible Bending and Guest Molecule Release of Azobenzene-Containing Polydiacetylene Nanotubes

Creation of hollow, one-dimensional nanomaterials has gained great recent attention in the chemical and material sciences. In a study aimed at discovering new functional materials of this type, we observed that an amphiphilic diacetylene (DA) derivative, containing an azobenzene moiety and an oligo-ethylene group, self-assembles to form nanotubes and undergoes photopolymerization to form hollow polydiacetylene (PDA) nanotubes with a uniform wall thickness and diameter. The azobenzene-PDA nanotubes are photoresponsive in that on-and-off UV-irradiation leads to a reversible morphological change between straight and bent forms in association with E-Z photoisomerization of the azobenzene group. Owing to the UV-induced structural change feature, the new DA and PDA nanotubes serve as a controlled release material. Accordingly, fluorescent rhodamine B encapsulated inside the nanotubes are effectively released by using repeated on-off UV irradiation. Furthermore, photo-release of rhodamine B was shown to occur in an artemia (brine shrimp).

Arylene Ethynylene-Functionalized Bithiazole-Based Zinc Polymers for Ultraefficient Photocatalytic Activity

Polymers 4 containing poly(arylene ethynylene) were synthesized and characterized systematically. Among them, 4c exhibited a remarkable H2 evolution rate (14.32 mmol h-1 g-1) with visible-light irradiation, lasting 72 h in different water qualities; the corresponding apparent quantum yield was 11.6% at 450 nm.

Glass-transition-induced color-changing resins containing layered polydiacetylene

A phase-segregated composite of polystyrene (PSt) and layered polydiacetylene (PDA) was formed through simultaneous polymerization and crystallization. As the motion of PSt chains with glass transition is transferred to that of PDA, the color change was achieved by the shortening of the conjugation length with deformation of the layered structure.

Preparation and Single Crystal Structure Determination of the First Biobased Furan-Polydiacetylene Using Topochemical Polymerization

Crystal structure elucidations of bio-based polymers provide invaluable data regarding structure–property relationships. In this work, we achieved synthesis and Single Crystal X-ray Diffraction (SCXRD) structural determination of a new furan-based polydiacetylene (PDA) derivative with carbamate (urethane) functionality. Firstly, diacetylene (DA) monomers were found to self-assemble in the crystalline state in such a way that the polymerization theoretically occurred in two different directions. Indeed, for both directions, geometrical parameters for the reactive alignment of DA are satisfied and closely related with the optimal geometrical parameters for DA topochemical polymerization (d(1) = 4.7–5.2 Å, d(2) ≤ 3.8 Å, θ ≈ 45°). However, within the axis of hydrogen bonds (HB), the self-assembling monomers display distances and angles (d(1) = 4.816 Å, d(2) = 3.822 Å, θ = 51°) that deviate more from the ideal values than those in the perpendicular direction (d(1) = 4.915Å, d(2) = 3.499Å, θ ≈ 45°). As expected from these observations, the thermal topochemical polymerization occurs in the direction perpendicular to the HB and the resulting PDA was characterized by SCXRD.

Cation-Directed Self-Assembly of Macrocyclic Diacetylene for Developing Chromogenic Polydiacetylene

The cation-directed self-assembly process has emerged as a fascinating approach for constructing supramolecular architectures and manifested a diverse range of assembly related applications. Herein, we synthesized a macrocyclic structure containing bis-amidopyridine and photopolymerizable diacetylene template, PyMCDA. Owing to the metal coordination affinity of bis-amidopyridine and the π-π stacking characteristic of diacetylene template and complementary to the cyclic molecular framework, Cs⁺-directed organic nanotubes are generated via unidirectional self-assembly of PyMCDA. The monomeric PyMCDA nanotubes are transformed into the covalently cross-linked chromogenic polydiacetylene nanotubes (PyMCPDA-Cs⁺) by UV-promoted topochemical polymerization. The result of a metal-ligand coordination characteristic, geometric parameters in solid-state assemblies, and topochemical polymerization behavior reveals a generation of Cs⁺ ion inserted nanotubes. Interestingly, PyMCDA-Cs⁺ nanotubes display thermochromic property with a brilliant blue-to-red color transition.

Covalently Linked Perylene Diimide-Polydiacetylene Nanofibers Display Enhanced Stability and Photocurrent with Reversible FRET Phenomenon

Because of their unique structural and optical properties, 1D perylene diimide (PDI) derivatives have gained attention for use in optoelectronic devices. However, PDI-containing self-assembled supramolecular systems often are of limited use because they have supramolecular architectures that are held together by weak noncovalent π-π stacking, hydrogen bonding, and hydrophobic interactions. As a result, they are intrinsically unstable under solution-processing conditions. To overcome this limitation, a polydiacetylene (PDA)-based strategy is developed to construct a solvent-resistant and stable PDI assembly. For this purpose, first the monomer PDI-BisDA is generated, in which two polymerizable diacetylene (DA) units are covalently linked to a PDI core. Importantly, 254 nm UV irradiation of self-assembled PDI-BisDA nanofibers forms solvent-resistant and stable PDI-PDA fibers. Owing to the presence of PDA, the generated polymer fibers display an increased photocurrent. In addition, the existence of PDA and PDI moieties in the fiber leads to the occurrence of switchable on-off fluorescence resonance energy transfer (FRET) between the PDI and reversibly thermochromic PDA chromophores.

A simple colorimetric sensor for the detection of moisture in organic solvents and building materials: applications in rewritable paper and fingerprint imaging

A simple off-the-shelf dye molecule, 1,4-dihydroxy-9,10-anthraquinone or quinizarin (1), has been investigated for the effective detection of moisture in organic solvents and building materials. Anion-induced deprotonation of 1 to 1.F followed by re-protonation with water is the working principle of the sensor system. Changes in colour, UV-Vis spectra and emission intensity indicate the moisture detection of 1.F in various organic solvents. The probe 1.F is more effective at the detection of water in acetonitrile and THF with a LOD of 0.0011 and 0.0026 wt%. Probe 1.F is reversible, reusable, highly selective, and sensitive and has a fast response time both in solution phase and in test papers. Probe 1.F is also applied for the detection of unknown moisture content in raw building materials such as cement, fly ash, foundry sand, and limestone. 1.F incorporated cellulose-based papers are applicable for inkless writing and stamping in the read-erase manner. Furthermore, these papers are also suitable for fingerprint imaging and sweat pore mapping by the simple colour change method.

Mini-review on an engineering approach towards the selection of transition metal complex-based catalysts for photocatalytic H2 production

Advances in transition-metal (Ru, Co, Cu, and Fe) complex-based catalysts since 2000 are briefly summarized in terms of catalyst selection and application for photocatalytic H₂ evolution.

Retracted Article: Facile preparation of bithiazole-based material for inkjet printed light-emitting electrochemical cell

Light-emitting electrochemical cell of bithiazole-based material was fabricated by solution processing rendered high external quantum efficiency over 12.8% and luminance of 1.8 10⁴ cd m⁻².

Light-emitting electrochemical cell of bithiazole-based material was fabricated by solution processing rendered high external quantum efficiency over 12.8% and luminance of 1.8 10⁴ cd m^−2.

Reversibly Thermochromic Cyclic Dipeptide Nanotubes

Owing to their capability of forming extensive hydrogen bondings and the facile introduction of chirality, cyclic dipeptides (CDPs) have gained great attention as scaffolds for functional supramolecules. Surprisingly, introduction of a photopolymerizable diacetylene (DA) moiety to the CDP afforded nanotubular structures with enhanced stability and reversible thermochromism. A series of CDP-containing DAs (CDP-DAs) are prepared by coupling 10,12-pentacosadiynoic acid with CDPs, cyclo(-Gly-Ser) and cis/trans cyclo(-Ser-Ser). Fabrication of CDP-DA self-assemblies in a polar chloroform and methanol solvent mixture affords nanotubes comprising single-wall and multiwall structures. The self-assembly behavior and morphology characteristic are examined by scanning electron microscopy and transmission electron microscopy. Next, X-ray diffraction analysis confirms well-ordered lamellar structures with a perfect agreement with the bilayer formation leading to the tubular structure via lamellar scrolling behavior. Upon UV irradiation, monomeric CDP-DA tubular assemblies result in the blue-colored CDP/polydiacetylene (PDA) nanotubes. Interestingly, CDP/PDA nanotubes exhibit a reversible blue-to-red color change for over 10 consecutive thermal cycles. The CDP-DA/PDA supramolecular system demonstrates potential applications in developing stimulus-responsive functional materials.

Visualization and Quantitative Detection of Friction Force by Self-Organized Organic Layered Composites

Visualization and quantitative detection of external stimuli are significant challenges in materials science. Quantitative detection of friction force, a mechanical stress, is not easily achieved using conventional stimuli-responsive materials. Here, the quantitative detection of friction force is reported, such as the strength and accumulated ammount, from the visible color of organic layered composites consisting of polydiacetylene (PDA) and organic amines without an excitation light source. The composites of the layered diacetylene monomer crystal and interlayer organic amine are synthesized through self-organization from the precursor solution. After topochemical polymerization, the layered composites based on PDA show tunable temperature-responsive and mechanoresponsive color-change properties depending on the types of interlayer amines. The layered composites are homogeneously coated on a filter paper. The change in color of the paper is quantitatively used to visualize the strength and accumulated amount of the applied friction force. Furthermore, writing pressure is measured by friction force using the paper device.

Monitoring Based on Narrow-Band Resonance Raman for "Phase-Shifting" π-Conjugated Polydiacetylene Vesicles upon Host-Guest Interaction and Thermal Stimuli

The present study reports a quantified monitoring by means of in situ resonance Raman scattering that analyzes phase-shifting characteristics of π-systems upon interacting with target analytes. A chemo- and thermochromic polydiacetylene vesicular probe is evaluated with multiple-wavelength Raman scattering modes in resonance with its phases, respectively, and thus can trace the phase-shifts. This Raman scattering-based analytical quantification is also successful in monitoring host-guest recognition events by utilizing much narrower bands, compared to those in conventional absorption or photoluminescence (PL) methods. As one of the outcomes, the monitoring analysis overcomes the limitations based on widely used colorimetric response (%CR) or PL that failed in the case of interaction with a surfactant, CTAB.

Recent progress in the stabilization of supramolecular assemblies with functional polydiacetylenes

This minireview covers the most recent examples of covalent rigidification of supramolecular self-assemblies through the photopolymerization of diacetylene moieties.