Fabrication of chitosan-based fluorescent hydrogel membranes cross-linked with bisbenzaldehyde for efficient selective detection and adsorption of Fe2

Chitosan, as a natural biomass material, is green, recyclable, sustainable and well biocompatible. The molecular chain is rich in active groups such as amino and hydroxyl groups, and its preparation of fluorescent probes has the advantages of biocompatibility and efficient detection performance. In this study, a bis(benzaldehyde) (BHD) fluorescent functional molecule was designed. Then a series of fluorescent chitosan-based hydrogel films (CSBHD) were prepared using chitosan as raw material and BHD as cross-linking agent. As a fluorescent probe for metal ions, CSBHD was able to efficiently detect Fe2+ with a linear correlation of fluorescence intensity in the range of 0-160 μM, and the limit of detection (LOD) was 0.55 μM. Moreover, it has excellent adsorption performance for Fe2+ ions, with a maximum adsorption capacity of 223.5 g/mg at 500 mg/L Fe2+ concentration. Finally, we characterised the structure and microscopic morphology of CSBHD films and found that CSBHD as a hydrogel film has a high cross-linking density, good water resistance, excellent thermal stability, strong resistance to swelling, and excellent stability in cycling tests. Hence, it has great potential for application in adsorption and detection of Fe2+ ions. It also provides a good strategy for the application of chitosan based fluorescent probe materials in environmental monitoring and heavy metal ion adsorption.

Crystal structure of (E)-N′-benzylidene-4-nitrobenzohydrazide – methanol (1/1), C15H15N3O4

C15H15N3O4, monoclinic, P21/c (no. 14), a = 13.5787(12) Å, b = 6.5393(5) Å, c = 16.3645(14) Å, β = 94.598(8)°, V = 1448.4(2) Å3, Z = 4, R gt (F) = 0.0465, wR ref (F 2) = 0.1106, T = 149.99(10) K.

Polymeric Emissive Materials Based on Dynamic Covalent Bonds

Dynamic covalent polymers, composed of dynamic covalent bonds (DCBs), have received increasing attention in the last decade due to their adaptive and reversible nature compared with common covalent linked polymers. Incorporating the DCBs into the polymeric material endows it with advanced performance including self-healing, shape memory property, and so forth. However, the emissive ability of such dynamic covalent polymeric materials has been rarely reviewed. Herein, this review has summarized DCBs-based emissive polymeric materials which are classified according to the different types of DCBs, including imine bond, acylhydrazone bond, boronic ester bond, dynamic C-C bond, as well as the reversible bonds based on Diels–Alder reaction and transesterification. The mechanism of chemical reactions and various stimuli-responsive behaviors of DCBs are introduced, followed by typical emissive polymers resulting from these DCBs. By taking advantage of the reversible nature of DCBs under chemical/physical stimuli, the constructed emissive polymeric materials show controllable and switchable emission. Finally, challenges and future trends in this field are briefly discussed in this review.

Dynamic Covalent Chemistry Constrained Diphenylethenes: Control over Reactivity and Luminescence in both Solution and Solid State

Diarylethenes (DAEs) are an important class of building blocks in chemistry and materials science, and hence, their modulation and functionalization are of critical significance. Here we demonstrate a general strategy...

A biocompatible hydrogel as a template for oxidative decomposition reactions: a chemodosimetric analysis and in vitro imaging of hypochlorite

The self-assembly properties of new biocompatible, thermoreversible fluorescent hydrogels, composed of amino acid residues have been reported. A unique gel-to-sol transition is triggered by chemodosimetric interaction in the presence of hypochlorite.

Hierarchical Self-Assembly and Multidynamic Responsiveness of Fluorescent Dynamic Covalent Networks Forming Organogels

Smart stimuli-responsive fluorescent materials are of interest in the context of sensing and imaging applications. In this project, we elaborated multidynamic fluorescent materials made of a tetraphenylethene fluorophore displaying aggregation-induced emission and short cysteine-rich C-hydrazide peptides. Specifically, we show that a hierarchical dynamic covalent self-assembly process, combining disulfide and acyl-hydrazone bond formation operating simultaneously in a one-pot reaction, yields cage compounds at low concentration (2 mM), while soluble fluorescent dynamic covalent networks and even chemically cross-linked fluorescent organogels are formed at higher concentrations. The number of cysteine residues in the peptide sequence impacts directly the mechanical properties of the resulting organogels, Young's moduli varying 2500-fold across the series. These materials underpinned by a nanofibrillar network display multidynamic responsiveness following concentration changes, chemical triggers, as well as light irradiation, all of which enable their controlled degradation with concomitant changes in spectroscopic outputs─self-assembly enhances fluorescence emission by ca. 100-fold and disassembly quenches fluorescence emission.

Fluorescent dialdehyde-BODIPY chitosan hydrogel and its highly sensing ability to Cu2+ ion

Fluorescent hydrogel with proper hydrophilicity and thermal stability, excellent sensitivity and high selectivity has important practical and scientific significance, especially in heavy metal ion detection. In this work, by adjusting the content of [2, 6-Bis-[4-formylthiophene]]-1,3,5,7-tetramethyl-8-phenyl-4, 4-difluoroborazaindoloene (B3), as a cross-linking agent, a series of chitosan- fluoroboron dipyrrole-chitosan-based fluorescent hydrogels (CBC) with large stokes shift were designed and prepared. The hydrogels can be used as fluorescent probes for identifying Cu²⁺ in aqueous solution. The linear quenching range of Cu²⁺ is 0-50 μM, and the detection limit and quenching constant are 4.75 μM and 3.52 × 10⁴ M^-1, respectively. Under the interaction of Cu²⁺, the imine bond CN was converted to C- N bond, which causes the phenomenon of fluorescence quenching. In addition, relatively high crosslink density improves hydrophilicity and thermal stability of initial chitosan, and made the swelling ability better.

Halogen Bonding Tetraphenylethene Anion Receptors: Anion-Induced Emissive Aggregates and Photoswitchable Recognition

A series of tetraphenylethene (TPE) derivatives functionalized with highly potent electron-deficient perfluoroaryl iodo-triazole halogen bond (XB) donors for anion recognition are reported. 1 H NMR titration experiments, fluorescence spectroscopy, dynamic light scattering measurements, TEM imaging and X-ray crystal structure analysis reveal that the tetra-substituted halogen bonding receptor forms luminescent nanoscale aggregates, the formation of which is driven by XB-mediated anion coordination. This anion-coordination-induced aggregation effect serves as a powerful sensory mechanism, capable of luminescence chloride sensing at parts per billion concentration. Furthermore, the doubly substituted geometric isomers act as unprecedented photoswitchable XB donor anion receptors, where the composition of the photostationary state can be modulated by the presence of a coordinating halide anion.

Aggregation-Induced Emission-Active Gels: Fabrications, Functions, and Applications

Chromophores that exhibit aggregation-induced emission (i.e., aggregation-induced emission luminogens [AIEgens]) emit intense fluorescence in their aggregated states, but show negligible emission as discrete molecular species in solution due to the changes in restriction and freedom of intramolecular motions. As solvent-swollen quasi-solids with both a compact phase and a free space, gels enable manipulation of intramolecular motions. Thus, AIE-active gels have attracted significant interest owing to their various distinctive properties and promising application potential. Herein, a comprehensive overview of AIE-active gels is provided. The fabrication strategies employed are detailed, and the applications of AIEgens are summarized. In addition, the gel functions arising from the AIE moieties are revealed, along with their structure-property relationships. Furthermore, the applications of AIE-active gels in diverse areas are illustrated. Finally, ongoing challenges and potential means to address them are discussed, along with future perspectives on AIE-active gels, with the overall aim of inspiring research on novel materials and ideas.

Recognition, mechanistic investigation and applications for the detection of biorelevant Cu2+/Fe2+/Fe3+ ions by ruthenium(ii)-polypyridyl based fluorescent sensors

Selective recognition of biorelevant Cu²⁺ and Fe²⁺/Fe³⁺ ions using fluorescent Ru(ii)-polypyridyl based sensors via both “turn-on” and “turn-off” emissive response is the main focus of present article.

Cyanide Sensing in Water Using a Copper Metallogel through "Turn-on" Fluorescence

The development of fluorescent probes for selective detection of cyanide has gained considerable attention over the past two decades due to benefits like high selectivity as well as sensitivity, fast response, visual output, accurate quantification, and a simplified sample preparation procedure. However, the propensity of supramolecular gels toward fluorescence sensing of cyanide in aqueous medium is not well explored until now. Herein, we report the design and synthesis of a novel copper based metallogel capable of sensing cyanide in water by fluorescence "turn on". Toward this, a terpyridine attached poly(aryl ether) dendrone derivative (G1) is synthesized which forms gel and exhibits Aggregation Induced Emission (AIE). The addition and diffusion of copper ions to the gel resulted in the formation of a nonluminescent copper metallogel (CuG). The copper metallogel could selectively sense cyanide in water by a fluorescence "turn-on" signal due to the regeneration of the AIE active gel. The mechanistic pathways of the sensing have been studied, and the detection limit for sensing was found to be as low as 1.09 μM. A thin film of CuG was prepared by casting the gel and used as a test strip for the visual detection of cyanide in water.

A C3-symmetrical tripodal acylhydrazone organogelator for the selective recognition of cyanide ions in the gel and solution phases: practical applications in food samples

The method of formation of low-molecular-weight organogelators via modifications in the substituents has been demonstrated. The organogelator formed can selectively sense cyanide ions in the gel and solution phases. Interaction of cyanide with acylhydrazone was noticeably visible to the "naked eye" and was proved using 1H NMR titrations. Notably, the ligand has been successfully explored for the recognition of cyanide ions in food samples. Additionally, low-cost cotton swabs coated with the organogelator showed rapid, on-site recognition of cyanide ions. The structure-property relationship discovered in the given study provides insight into the development of novel, cost-effective multifunctional materials.

Multi-Stimuli Responsive FRET Processes of Bifluorophoric AIEgens in an Amphiphilic Copolymer and Its Application to Cyanide Detection in Aqueous Media

A novel amphiphilic aggregation-induced emission (AIE) copolymer, that is, poly(NIPAM-co-TPE-SP), consisting of N-isopropylacrylamide (NIPAM) as a hydrophilic unit and a tetraphenylethylene-spiropyran monomer (TPE-SP) as a bifluorophoric unit is reported. Upon UV exposure, the close form of non-emissive spiropyran (SP) in poly(NIPAM-co-TPE-SP) can be photo-switched to the open form of emissive merocyanine (MC) in poly(NIPAM-co-TPE-MC) in an aqueous solution, leading to ratiometric fluorescence of AIEgens between green TPE and red MC emissions at 517 and 627 nm, respectively, via Förster resonance energy transfer (FRET). Distinct FRET processes of poly(NIPAM-co-TPE-MC) can be observed under various UV and visible light irradiations, acid-base conditions, thermal treatments, and cyanide ion interactions, which are also confirmed by theoretical studies. The subtle perturbations of environmental factors, such as UV exposure, pH value, temperature, and cyanide ion, can be detected in aqueous media by distinct ratiometric fluorescence changes of the FRET behavior in the amphiphilic poly(NIPAM-co-TPE-MC). Moreover, the first FRET sensor polymer poly(NIPAM-co-TPE-MC) based on dual AIEgens of TPE and MC units is developed to show a very high selectivity and sensitivity with a low detection limit (LOD = 0.26 μM) toward the cyanide ion in water, which only contain an approximately 1% molar ratio of the bifluorophoric content and can be utilized in cellular bioimaging applications for cyanide detections.

Pteridine derivatives: novel low-molecular-weight organogelators and their piezofluorochromism

Here, π-conjugated compounds based on pteridine derivatives were synthesized and their self-assembling behaviors in a variety of organic solvents and piezofluorochromism were studied.

Post-synthetic modification of a metal–organic framework with a chemodosimeter for the rapid detection of lethal cyanide via dual emission

A post-synthetically modified chemodosimeter grafted MOF is presented for the selective, visual and fluorogenic detection of cyanide via dual emission.

Multi-functional organic gelator derived from phenyllactic acid for phenol removal and oil recovery

Supramolecular gels, a fascinating class of soft materials, are of great interest for their wide applications. In this work, a series of organic gelators derived from phenyllactic acid were prepared, and their gelation properties were further investigated. It was found that the gelator 1e bearing a hydrazine moiety could congeal 17 kinds of common organic liquids (polar and non-polar) efficiently. Meanwhile, the morphological structures and dominant factors of the gel were examined by scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), concentration and temperature-dependent ¹H NMR. Crucially, the gelator displayed outstanding performances in toxic phenol removal and spilled oil and petroleum products recovery. Moreover, it also displayed a satisfactory recyclability, which will greatly promote its application in practice. These impressive results will provide a novel avenue for the water treatment and the development of functional supramolecular gel materials.

Stability, Stimuli-Responsiveness, and Versatile Sorption Properties of a Dynamic Covalent Acylhydrazone Gel

Gel adsorbents are promising for pollutant removal from the wastewater. Herein, an acylhydrazone gel is developed from acylhydrazide-terminated pentaerythritol (PAT) and 2,4,6-triformylphloroglucinol (TFP) based on dynamic covalent acylhydrazone chemistry. PAT-TFP gel is stable under various conditions, while it shows reversible Cu2+ adsorption and desorption. PAT-TFP gel is studied as a versatile adsorbent for the capture of a range of (bulky) organic contaminants and heavy metal ions from aqueous solutions. Fast and good adsorption capacities are achieved for various dyes (rhodamine B and methyl orange), amines (aniline, p-chloroaniline, 4-methylaniline, and p-aminobenzoic acid), phenols (phenol, 1-naphthol, p-methylphenol, and bisphenol A), and metal ions (Cu2+, Cr3+, and Hg2+). The maximum adsorption capacity is 107.5 mg g-1 for Cu2+ and the equilibrium adsorption time is 30 min. PAT-TFP gel can be regenerated efficiently and used repeatedly.

Chirality transfer based on dynamic covalent chemistry: from small chiral molecules to supramolecules

Chirality transfer from small molecule to supramolecule was successfully achieved via regulation of dynamic covalent chemistry.

Multi-stimuli-responsiveness of a novel polydiacetylene-based supramolecular gel

Herein, a novel supramolecular gel was fabricated through the bi-component co-assembly strategy of commercially available 10,12-pentacosadiynoic acid (PCDA) and laboratory-synthesized amphiphilic co-gelator N-(2-(1H-imidazol-4-yl)ethyl)stearamide (IMSA), which contains one imidazole head group and a long alkyl chain tail, by synergetic noncovalent interactions. Upon irradiation of normal 254 nm UV light, blue polydiacetylene (PDA) could be obtained by topo-polymerization of the PCDA monomers in the gel phase. This PDA-based supramolecular gel is able to respond to various environmental stimuli and shows a blue-to-red chromatic transition, which could be observed by the naked eye. Specifically, upon exposure to heat, pH, metal cation and organic solvent stimuli, the PDA gel displays thermochromism, halochromism, ionochromism and solvatochromism, respectively. More interestingly, the differences of the above-mentioned stimuli-induced color transition of the blue PDA supramolecular gels could be characterized by UV-Vis absorption spectra and Raman spectra, therefore illuminating a bright application prospect in the area of chemosensing.

A tetravalent sialic acid-coated tetraphenylethene luminogen with aggregation-induced emission characteristics: design, synthesis and application for sialidase activity assay, high-throughput screening of sialidase inhibitors and diagnosis of bacterial vaginosis

We report a turn-on tetravalent sialic acid-coated tetraphenylethene luminogen (TPE4S) with excellent hydrophilicity, good stability, high sensitivity and unique selectivity towards sialidases, and the maximum fluorescence enhancement was ∼40 fold. More importantly, TPE4S was successfully utilized for the screening of sialidase inhibitors and diagnosis of bacterial vaginosis.