Functionality-Oriented Derivatization of Naphthalene Diimide: A Molecular Gel Strategy-Based Fluorescent Film for Aniline Vapor Detection

Molecular design and architectonics towards film-based fluorescent sensing

The past few decades have witnessed encouraging progress in the development of high-performance film-based fluorescent sensors (FFSs) for detecting explosives, illicit drugs, chemical warfare agents (CWAs), and hazardous volatile organic chemicals (VOCs), among others. Several FFSs have transitioned from laboratory research to real-world applications, demonstrating their practical relevance. At the heart of FFS technology lies the sensing films, which play a crucial role in determining the analytes and the resulting signals. The selection of sensing fluorophores and the fabrication strategies employed in film construction are key factors that influence the fluorescence properties, active-layer structures, and overall sensing behaviors of these films. This review examines the progress and innovations in the research field of FFSs over the past two decades, focusing on advancements in fluorophore design and active-layer structural engineering. It underscores popular sensing fluorophore scaffolds and the dynamics of excited state processes. Additionally, it delves into six distinct categories of film fabrication technologies and strategies, providing insights into their advantages and limitations. This review further addresses important considerations such as photostability and substrate effects. Concluding with an overview of the field's challenges and prospects, it sheds light on the potential for further development in this burgeoning area.

Facile one-pot multicomponent synthesis of peptoid based gelators as novel scaffolds for drug incorporation and pH-sensitive release

Infections caused by bacteria are the primary cause of illness and death globally, and antibiotics are the most commonly used medications to treat them. However, there are certain inherent problems in administering these drugs without any changes to their effectiveness. In order to sustain the targeted dosage over time, the use of a biocompatible local drug delivery system using low molecular mass gelators is preferred as a potential approach to reduce its side effects. Low molecular weight organic gelators (LMWOGs) have drawn a lot of attention due to their numerous and varied applications in multiple fields. But nowadays its quite a challenging task to synthesize new types of LMWOGs that can fill the significant gap towards potential applications. In this work, we have explored a multicomponent pathway for the synthesis of a small repertoire of peptoids from simple building blocks by a one-pot Ugi reaction. A variety of novel effective low molecular weight organic gelators have been synthesized, leading to the formation of stable self-assembled aggregates in various solvents such as DMSO, aqueous DMSO, and methanol. Consequently, these aggregates give rise to the creation of organogels and organo/hydrogels. The gels have a minimum gelation concentration (MGC) of 1-2% w/v with high thermal stability. Furthermore, successful encapsulation and release of metronidazole (MZ) were achieved within the gel matrix under physiological pH conditions at 37 °C, ensuring the preservation of its structural and functional properties. The results demonstrated that the release rate of MZ from the organo/hydrogels is contingent on pH, exhibiting a gradual and regulated release in mild alkaline environments. Moreover, the devised system displayed noteworthy antimicrobial efficacy against E. coli, underscoring the potential of these novel low molecular weight organic gels (LMWOGs) as effective drug delivery systems in the pharmaceutical industry. The gel formulations exhibit biocompatibility and negligible cytotoxicity, as evidenced by cell viability studies conducted using the MTT assay.

Self-Assembly of a Series of Carbazole-Based Vinyl-benzoxazole Derivatives in Gel Phases

A series of carbazole-based vinyl-benzoxazole derivatives have been synthesized in order to verify whether X-ray diffraction (XRD) simulation can give more information about intermolecular stacking in the gel phase. It was found that their gelation capabilities were strongly dependent on the length of the alkyl chain. The compounds with shorter alkyl chains have lower critical gelation concentrations (CGCs) in nonpolar alkane and alcohols with longer carbon chains. On the other hand, compounds with long alkyl chains presented small CGCs in polar methanol. Powder XRD structure solution gave more information about intermolecular stacking than the traditional way of analyzing diffraction peaks to derive approximate molecular stacking patterns. The results verified that gelators had a similar head-to-tail π-stacking between aromatic groups in gel phases although different slipping angles existed. Moreover, ordered stacking between the alkyl chains was also present.

Extended π-Conjugation and Structural Planarity Effects of Symmetrical D-π-A-π-D Naphthalene and Perylene Diimide Semiconductors on n-type Electrical Properties

A series of donor-π-acceptor-π-donor (D-π-A-π-D) compounds based on naphthalendiimide (NDI) and perylenediimide (PDI) central cores combined with triphenylamine and phenylcarbazole donor groups have been synthesized, characterized and tested in top-contact/bottom gate organic field-effect transistors (OFETs). The results showed high electron mobilities, up to 0.3 cm2  V-1  s-1 , in the case of NDI derivatives and moderate values of around 10-3  cm2  V-1  s-1 for PDI-based semiconductors. Quantum chemical calculations were performed in order to support the experimental data. The results suggest that adequate molecular characteristics and larger crystalline domains in NDI vs. PDI semiconducting films may be the reasons behind the enhanced electrical properties of NDI derivatives. Furthermore, when the lateral donor substituents are triphenylamine groups, the mobilities were slightly higher in comparison to phenylcarbazole donor groups due to an improved electron-donating character. Other characterization techniques, such as AFM, X-ray diffraction or spectroelectrochemistry, among others, have been performed to analyze supramolecular order, charge carriers' nature and stability, parameters closely related to charge transport characteristics.

Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroamination

Implementing chemical reactivity into synthetic supramolecular polymers based on π-conjugated molecules has been of great interest to create functional materials with spatiotemporal dynamic properties. However, the development of an in situ chemical reaction within supramolecular polymers is still in its infancy, because one needs to design optimal π-conjugated monomers having excellent reactivity under mild conditions possibly without byproducts or a catalyst. Herein we report the synthesis of a supramolecular polymer based on ethynyl core-substituted naphthalenediimide (S-NDI2) molecules that react with various amines quantitatively in a nonpolar solvent, without a catalyst, at 298 K. Most interestingly, the in situ reaction of the S-NDI2 supramolecular polymer with a linear aliphatic diamine proceeded much faster than the homogeneous reaction of a monomeric naphthalenediimide with the same diamine, affording diamine-linked S-NDI2 oligomers and polymers. The acceleration of in situ hydroamination was presumably due to rapid intra-supramolecular cross-linking between ethynyl and amino groups fixed in close proximity within the supramolecular polymer. Such intra-supramolecular cross-linking did not occur efficiently with an incompatible diamine. The systematic kinetic studies of in situ catalyst-free hydroamination within supramolecular polymers provide us with a useful, facile and versatile tool kit for designing dynamic supramolecular polymeric materials based on electron-deficient π-conjugated monomers.

Naphthalene diimides: perspectives and promise

In this review, we describe the developments in the field of naphthalene diimides (NDIs) from 2016 to the presentday. NDIs are shown to be an increasingly interesting class of molecules due to their electronic properties, large electron deficient aromatic cores and tendency to self-assemble into functional structures. Almost all NDIs possess high electron affinity, good charge carrier mobility, and excellent thermal and oxidative stability, making them promising candidates for applications in organic electronics, photovoltaic devices, and flexible displays. NDIs have also been extensively studied due to their potential real-world uses across a wide variety of applications including supramolecular chemistry, sensing, host-guest complexes for molecular switching devices, such as catenanes and rotaxanes, ion-channels, catalysis, and medicine and as non-fullerene accepters in solar cells. In recent years, NDI research with respect to supramolecular assemblies and mechanoluminescent properties has also gained considerable traction. Thus, this review will assist a wide range of readers and researchers including chemists, physicists, biologists, medicinal chemists and materials scientists in understanding the scope for development and applicability of NDI dyes in their respective fields through a discussion of the main properties of NDI derivatives and of the status of emerging applications.

Metal Cation Triggered Peptide Hydrogels and Their Application in Food Freshness Monitoring and Dye Adsorption

Metal-ligand interactions have emerged as an important tool to trigger and modulate self-assembly, and to tune the properties of the final supramolecular materials. Herein, we report the metal-cation induced self-assembly of a pyrene-peptide conjugate to form hydrogels. The peptide has been rationally designed to favor the formation of β-sheet 1D assemblies and metal coordination through the Glu side chains. We studied in detail the self-assembly process in the presence of H+, Li+, Na+, K+, Ca2+, Ni2+, Cu2+, Zn2+, Cd2+, Co2+, Fe3+, and Cr3+ and found that the morphology and mechanical properties of the hydrogels are ion-dependent. Moreover, thanks to the presence of the metal, new applications could be explored. Cu2+ metallogels could be used for amine sensing and meat freshness monitoring, while Zn2+ metallogels showed good selectivity for cationic dye adsorption and separation.

Diethylamine fluorescence sensor based on silica hollow sphere photonic crystals

In this study, based on silica hollow sphere photonic crystals (SHSPCs), a simple and selective fluorescence sensor for high-performance diethylamine detection was developed. The sensor does not involve complicated integration of arrays or tedious synthetic work. During the detection, the SHSPCs could significantly enhance the fluorescence intensity of rhodamine 6G (Rh6G), and meanwhile, adsorb some Rh6G on their surface. Due to the competitive adsorption, diethylamine could free the Rh6G which was adsorbed on the surface of the SHSPCs, thus enhancing the fluorescence emission intensity with the increase of Rh6G concentration. The second enhancement of the fluorescence emission enabled the selective detection of diethylamine. It is remarkable that a simple and readily available dye (Rh6G) facilitates the efficient detection of diethylamine. Moreover, the sensor has good interference immunity, stability and reusability.

High-Performance Sensing of Formic Acid Vapor Enabled by a Newly Developed Nanofilm-Based Fluorescent Sensor

Although it is widely used in industry and food products, formic acid can be dangerous owing to its corrosive properties. Accurate determination of formic acid would not only benefit its qualified uses but also be an effective way to avoid corrosion or injury from inhalation, swallowing, or touching. Herein, we present a nanofilm-based fluorescent sensor for formic acid vapor detection with a wide response range, fast response speed, and high sensitivity and selectivity. The nanofilm was synthesized at a humid air/dimethyl sulfoxide (DMSO) interface through dynamic covalent condensation between two typically designed building blocks, de-tert-butyl calix[4]arene-tetrahydrazide (CATH) and 4,4',4″,4‴-(ethene-1,1,2,2-tetrayl)tetra-benzaldehyde (ETBA). The as-prepared nanofilm is uniform, flexible, fluorescent, and photochemically stable. The thickness and fluorescence intensity of the nanofilm can be facilely adjusted by varying the concentration of the building blocks and the sensing performance of the nanofilm can be optimized accordingly. Based on the nanofilm, a fluorescent sensor with a wide response range (4.4 ppt-4400 ppm) for real-time and online detection of formic acid vapor was built. With the sensor, a trace amount (0.01%) of formic acid in petroleum ether (60-90 °C) can be detected within 3 s. Besides, fluorescence quenching of the nanofilm by formic acid vapor can be visualized. It is believed that the sensor based on the nanofilm would find real-life applications in corrosion and injury prevention from formic acid.

A shape-persistent arylene ethynylene macrocycle with a multiple acetamide modified cavity: synthesis and gelation

A new arylene ethynylene macrocycle (AEM) molecule bearing endo-acetamide groups was obtained by a Pd/Cu mediated homo-coupling reaction. Introducing tetraethylene glycol ether as a linkage between two C-shaped fragments substantially improved the final cyclization yield (30%). Concentration-dependent ¹HNMR experiments indicated that strong aggregates formed through H-bonds were observed for this new macrocycle with amide groups in solution. And also, this macrocycle was fluorescent in solution and showed a highly selective fluorescence quenching response toward the highly toxic Hg²⁺. More importantly, this macrocycle could induce gelation of several solvents. Significantly, an interesting aggregation-induced enhanced emission (AIEE) behavior was observed for this macrocycle upon gelation. Both SEM and TEM investigations revealed that nanoporous structures existed in the xerogels. This study offers a new molecular design approach to develop fluorescent gels from planar AEM molecules with a functional cavity.

Transformable fluorescent nanoparticles (TFNs) of amphiphilic block copolymers for visual detection of aromatic amines in water

A kind of novel transformable fluorescent nanoparticle made of block copolymers is constructed for the sensitive detection of aromatic amines in water.

Radical anion formation exhibiting "turn-on" fluorescence sensing of hydrazine using a naphthalene diimide (NDI) derivative with a donor-acceptor-donor (D-A-D) molecular structure

In this paper, the synthesis of a naphthalene diimide (NDI) derivative with a donor-acceptor-donor (D-A-D) molecular structure substituted with a long alkyl chain (12 carbons) containing naphthalene hydrazide at the imide position is reported. The reduced emission quantum yield (φf = 0.01-0.03) of the NDI derivative in various solvents indicates the perturbation of the electronic state of π-electron deficient NDI (A) by the peripheral naphthalene (D) units. The investigation of the influence of the alkyl chain and naphthalene substituent on the self-assembling properties of the NDI derivative reveals an isodesmic mode of self-assembly in a chloroform/methylcyclohexane (CHCl3/MCH, 1 : 9, v/v) mixture. The self-assembling nature of the NDI derivative also results in the formation of an organogel in the CHCl3/MCH (1 : 9, v/v) mixture, and gel formation is well-comprehended by techniques such as P-XRD, rheological studies, and FT-IR measurements. Furthermore, radical anion (NDI˙-) formation of π-acidic NDI was used as a sensing tool for hydrazine by a fluorescence "turn-on" (φf = 0.12) method in the solution (DMSO), film, and gel state with a detection limit of 284.1 ppb in DMSO and 32 ppb in the gel state.

A Self-Assembled Peptide-Appended Naphthalene Diimide: A Fluorescent Switch for Sensing Acid and Base Vapors

A histidine-containing bola-amphiphilic molecule (NDIP) containing a peptide-appended naphthalenediimide (NDI) forms fluorescent hydrogels in phosphate buffer and organogels with benzenoid solvents. These gels were characterized by several spectroscopic and microscopic techniques including FT-IR, HR-TEM, powder X-ray diffraction and small-angle X-ray scattering, UV-Vis and fluorescence studies. The gelator molecule exhibits no significant fluorescence in the xerogel state, while it shows a significant fluorescence (bright cyan) in the presence of volatile organic/inorganic acid vapors; this cyan color vanishes in presence of base (ammonia vapors). A reusable paper-strip-based method based on this self-assembled fluorescent material can be used to easily detect hazardous volatile acid and base vapors with the naked eye.

Ultrathin agaric-like ZnO with Pd dopant for aniline sensor and DFT investigation

Aniline detection is of great importance in many industries, but most of the aniline sensors suffers from tedious and time consuming process. Herein, we present an efficient aniline sensor based on Pd decorated ZnO nanomaterials. Ultrathin ZnO nanosheets were synthesized by a facile one-step hydrothermal method. The nanosheets were corrugated into a unique agaric morphology, endorsing the nanomaterials with high surface area that is ideal for gas sensing applications. The obtained ZnO nanosheets were then uniformly decorated with uniform Pd nanoparticles (Pd NPs) around 5 nm in diameter. Gas sensing experiment on the ZnO decorate with different amount of Pd nanoparticles were systematically evaluated. The sample decorated with 0.3 % Pd NPs (Pd-ZnO-0.3) exhibited the highest sensitivity to aniline, which is about two orders higher than that of the pure ZnO nanosheet. The gas sensor based on Pd-ZnO-0.3 has a detection limit to aniline down to 0.5 ppm, with very short response and recovery times of 29 s and 23 s, respectively to 100 ppm aniline. First-principles DFT study was employed to provide the sensing mechanism. The improved sensing performance could be attributed to the increasing adsorbed oxygen and tunable band alignment for Pd-ZnO materials. This work provides new insights to the design strategy of Pd-decorated ZnO nanomaterials for high performance gas sensors.

Eu(III) Tetrahedron Cage as a Luminescent Chemosensor for Rapidly Reversible and Turn-On Detection of Volatile Amine/NH3

Because of the involvement of the gas-solid diffusion, device fabrication, and the relatively complex photophysical process, the lanthanide complexes are rarely exploited as fluorescence sensors for volatile compound (VC) detection. Herein, we report the first example of a discrete 3D Ln-based architecture as a sensor for VCs. The designed Eu₄L₄ tetrahedral cage shows highly selective, rapidly reversible, and turn-on emissive responses toward volatile amines/NH₃ in a spin-coated film. Through the comprehensive spectral characteristic and density functional theory calculation, an intermolecular weak nucleophilic interaction is proposed for this response mechanism. Combining this weak interactions with the permeability of the cage, the film presents subsecond to second timescales rapid response; combining the fitting electrophilic capability of the β-diketonate units to amine nitrogen with the tunable intramolecular charge-transfer feature, the cage shows excellent selectivity and turn-on emissive response. This work provides a new clue to develop the lanthanide complexes as luminescence probes for VCs.

Discrimination of Various Amine Vapors by a Triemissive Metal-Organic Framework Composite via the Combination of a Three-Dimensional Ratiometric Approach and a Confinement-Induced Enhancement Effect

Multiemissive sensors are being actively pursued, because of their ratiometric luminescent detection capabilities, which demonstrates better sensitivity and selectivity than conventional single-emission sensors. Herein, we present a trichromatic white-light-emitting metal-organic framework (MOF) composite (Z3) by simultaneously incorporating red/green-emitting Pt/Ru complex cations into porous blue-emitting bio-MOF-1 through post-synthetic modification. With the help of a three-dimensional (3-D) dual-ratiometric luminescence recognition method, and unique turn-on responses of the red emission toward amine compounds (ACs), including NH₃ and aliphatic amines, via confinement-induced luminescence enhancement effect, Z3 can work as a dual-ratiometric luminescent sensor for discrimination of 7 out of 11 AC vapors. This work not only provides a new AC sensing mechanism (confinement effect) that can induce a "turn-on" response but also proves that the accuracy and selectivity of composite sensor can be greatly improved through the combination of 3-D recognition method and the confinement effect. Thus, it open up fresh opportunities to develop composite sensors with excellent sensing and differentiating ability.

Hydrogelation with a water-insoluble organogelator - surfactant mediated gelation (SMG)

The low-molecular-weight gelator (LMG) 12-hydroxyoctadecanoic acid (12-HOA) is insoluble in water, but can be solubilized in surfactant micelles. We therefore solubilized 12-HOA at 80 °C in an aqueous solution of cetyltrimethylammonium bromide (CTAB) containing spherical micelles. On cooling this system down to room temperature, a hydrogel is obtained. We will refer to this process as "surfactant-mediated gelation" (SMG). The hydrogels were formed at a lower 12-HOA concentration when sodium salicylate (NaSal) was added to the CTAB system, which induced the formation of wormlike micelles. Hydrogels obtained by SMG from spherical and wormlike micelles are referred to as gelled micellar phases (GMs) and gelled wormlike micellar phases (GWLMs), respectively. Optical microscopy and transmission electron microscopy (TEM) showed that 12-HOA forms self-assembled fibrillar networks (SAFiNs) in both GMs and GWLMs. The sol-gel transition temperature, T_sol-gel, of the GWLM samples was higher than that of the GM samples. Dynamic rheological measurements revealed gel properties (G' > G'' at all angular frequencies) for both gels; however, a higher viscoelasticity was observed for the GWLM samples, which in turn, was reflected in the higher T_sol-gel. Small- and wide-angle X-ray scattering (SWAXS) showed that micelles and gel fibers coexist in the GM and GWLM samples. Our study demonstrates the gelation of aqueous micellar solutions with water-insoluble LMGs.

Self-Amplified Fluorescent Nanoparticles for Rapid and Visual Detection of Xylene in Aqueous Media

Pollutant detection is of great importance for quality control of drinking water and environmental protection. The common methods of pollutant detection suffer from time-consuming procedures, bulky and expensive instruments, and complicated sample pretreatment. Herein, a type of conceptually new self-amplified fluorescent nanoparticle (SAFN) is constructed based on aggregation-induced emission (AIE) luminogens for rapid and visual detection of xylene in aqueous media. AIE luminogens are self-assembled into SAFNs in aqueous media, which emit efficiently due to the aggregation of luminogen molecules. The SAFNs of AIE luminogens stick xylene molecules from aqueous media through multiple interactions including hydrophobic and π-π interactions. Upon capturing xylene, SAFNs swell, which quench the fluorescence of the whole SAFNs, showing the self-amplification effect. Such a self-amplification effect is entirely different from that of conjugated polymers in the literature. Importantly, fluorescence quenching of SAFNs by xylene can be readily observed by the naked eye, which enables visual xylene sensing. The SAFNs enable rapid and visual detection of xylene in aqueous media with a low detection limit (5 μg/L) in the order of seconds. Given high sensitivity, rapid response, simple and easy operation, and low cost, SAFNs of AIE luminogens present a promising platform for visual detection of organic pollutants in aqueous media.

Reaction-Based, Fluorescent Film Deposition from Dopamine and a Diamine-Tethered, Bis-Resorcinol Coupler

The reaction-based deposition on various surfaces of an all-organic fluorescent coating is reported here, involving autoxidation of 2 mM dopamine in carbonate buffer at pH 9.0, in the presence of a 1 mM diamine–resorcinol coupler (Bis–Res) prepared from 2,4-dihydroxybenzaldehyde and hexamethylenediamine (HMDA). Spectral analysis of the films coupled with an LC-MS investigation of the yellow fluorescent mixture was compatible with the formation and deposition of HMDA-linked methanobenzofuroazocinone fluorophores. Both the emission properties and hydrophobicity of the film were abated in a reversible manner following exposure to acid vapors. These results provide an entry to efficient and practical fluorescent coating methodologies based on in situ generation and the deposition of wet adhesive, as well as fluorescent materials combining a strongly emitting fluorophore with the film-forming properties of long chain diamines.

Ru(III)-Based Metal-Organic Gels: Intrinsic Horseradish and NADH Peroxidase-Mimicking Nanozyme

Highly active, stable, and cost-effective enzyme-mimicking nanomaterials (nanozymes) hold the potential to be an alternative to replace natural enzymes for the catalysis of enzyme-like reactions in various applications. Here, novel 3D ruthenium-based metal-organic gels (Ru-MOGs) with fibrillar network structures have been successfully synthesized using a facile one-step strategy at room temperature. Surprisingly, the developed 3D fibrillar networked Ru-MOGs simultaneously possess intrinsic horseradish peroxidase and NADH peroxidase mimetic activities. Meanwhile, the horseradish peroxidase mimetic catalytic activity displays well in both acidic environment and alkaline condition. Kinetic analysis reveals that Ru-MOGs make an effective peroxidase mimic with exceptionally high catalytic velocity (V_m), substrate binding affinity (K_m), and catalytic efficiency (K_cat/K_m). Furthermore, as a proof-of-concept, the mimetic enzyme property of this material was further used to establish a chemiluminescent biosensing platform for glucose detection. These easily synthesized Ru-MOGs as highly active and novel nanozymes not only suggests a bright future for the nanomaterials as enzyme mimics but also provides new insights into the properties of MOGs, greatly broadening and advancing their applications in biocatalysis and bioassays.

Perylene Bisimide Aggregates as Probes for Subnanomolar Discrimination of Aromatic Biogenic Amines

Perylene bisimide derivatives show peculiar physical chemical features, such as a highly conjugated system, high extinction coefficients and elevated fluorescence quantum yields, making them suitable for the development of optical sensors of compounds of interest. In particular, they are characterized by the tendency to aggregate into π-π stacked supramolecular structures. In this contribution, the behavior of the PBI derivative N, N'-bis(2-(trimethylammonium)ethylene)perylene bisimide dichloride was investigated both in aqueous solution and on solid support. The electronic communication between PBI aggregates and biogenic amines was exploited in order to discriminate aromatic amines down to subnanomolar concentrations by observing PBI fluorescence variations in the presence of various amines and at different concentrations. The experimental findings were corroborated by density functional theory calculations. In particular, phenylethylamine and tyramine were demonstrated to be selectively detected down to 10^-10 M concentration. Then, in order to develop a surface plasmon resonance (SPR) device, PBI was deposited onto a SPR support by means of the layer-by-layer method. PBI was deposited in the aggregated form and was demonstrated to preserve the capability to discriminate, selectively and with an outstanding analytical sensitivity, tyramine in the vapor phase and even if mixed with other aromatic amines.

Sensitive and rapid detection of aliphatic amines in water using self-stabilized micelles of fluorescent block copolymers

A kind of self-stabilized micelles of fluorescent block copolymers are constructed for rapid and sensitive detection of aliphatic amines in water based on capture-report strategy. An amphiphilic triblock copolymer functionalized with aggregation induced emission (AIE) chromophores self assembles into micelles with core-shell structures in aqueous solution. Hydrophobic AIE chromophores organize into cores, where hydrophobic interaction among the AIE chromophores inhibits the micelles from disassembling. The cores of AIE chromophores are surrounded by a corona of water-soluble polymer segments, endowing the micelles with superior dispersibility in water. Water-soluble polymer segments capture organic amines in water due to preferential hydrophobic interactions between them. The enriched amines in the corona subsequently diffuse into hydrophobic cores of micelles, quenching fluorescence of the AIE chromophores. The fluorescent micelles allow rapid detection of aliphatic amines in the order of seconds at a concentration as low as 8 μg/L.

Instant hydrogel formation of terpyridine-based complexes triggered by DNA via non-covalent interaction

Biomolecule-based hydrogels have potential use in a wide range of applications such as controlled drug release, tissue engineering, and biofabrication. Herein, driven by specific interactions between ds-DNA (double-stranded DNA) and Zn2+ based metal-complexes, we report that the use of DNA as cross-linkers can enhance interactions between self-assembling Zn2+ complexes containing terpyridine and sugar groups in the generation of bioinspired hydrogels from solutions or suspensions. The gelation process is fast and straightforward without tedious steps and happens at room temperature. Such a hydrogelation process of different Zn2+ complexes endows the visualized and selective DNA analogue discrimination. Several experiments suggest that the strong intercalation binding of Zn2+ complexes with ds-DNA results in the unzipping of ds-DNA into ss-DNA (single-stranded DNA), which further behave as linkers to enhance the intermolecular interactions of self-assembling Zn2+ complex molecules via coordination interactions. This work demonstrates an efficient and universal strategy to prepare hydrogels based on biomolecular recognition. Moreover, the DNA responsive behaviors of Zn2+ complexes are further compared with that of solutions and cells.

Supramolecular Thermotropic Ionic Liquid Crystals Formed via Self-Assembled Zwitterionic Ionic Liquids

Supramolecular thermotropic ionic liquid crystals (ILCs) with hexagonal and lamellar phases were fabricated by the self-assembly of zwitterionic ionic liquids, which were formed by 3-(1-alkyl-3-imidazolio) propanesulfonate with different alkyl chain lengths C _nIPS ( n = 12, 14, 16) and 3,4,5-tris(dodecyloxy)benzoic acid (TDBA) based on intermolecular electrostatic interactions. The phase behaviors of ILCs were investigated by differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and polarized optical microscopy (POM). The highly ordered and well-defined microstructure of ILCs can be considered to be proton pathways and to radically improve the ionic conductivity, suggesting the induction of proton conduction through a hopping mechanism.

Fast, sensitive, selective and reversible fluorescence monitoring of TATP in a vapor phase

The development of sensors for the detection of triacetone triperoxide (TATP) has attracted great attention. Here, we constructed a low-cost, portable, reusable, visible paper-based fluorescent sensor for the sensitive detection of TATP via vapor sampling. Under optimized conditions, the fluorescent film showed a high sensitivity to TATP with a detection limit of lower than 0.5 μg mL-1 in air. The linear range of the response is from 0.5 to 8.0 μg mL-1. In addition, the paper-based sensor exhibited high selectivity to TATP. The presence of potential interferents showed little effect on sensing. Moreover, sensing is fully reversible. Fortunately, the test can also be conducted in a visualized way.

Self-healing gels triggered by ultrasound with color-tunable emission based on ion recognition

Herein, O-substituted terpyridine motif was used as both rigid fluorescent π core and ion binding site, in order to construct an novel amphiphilic organogelator TEC containing cholesterol unit. We demonstrated a ultrasound induced reversible sol-gel transition approach driven by adjusted non covalent interactions and the resulted gels showed self-healing properties and tunable emission color when incorporating inorganic ions into the gel matrices. By heating-cooling process, the gel transformed to sol again. Simultaneously, the vesicle-tube morphology transition controlled by sonication and heating-cooling was also observed, together with aggregation induced emission enhancement (AIE) property of the gel. The results suggested that ultrasound promoted the J aggregations of terpyridine motifs and enhanced the hydrogen bonding interactions of TEC molecules, leading to the gelation process.

Controlling the supramolecular polymerization and metallogel formation of Pt(ii) complexes via delicate tuning of non-covalent interactions

Direct influence of noncovalent ionic and hydrogen bonding interactions on supramolecular polymerization mechanisms and their impact on gel formation of luminescent platinum complexes have been comprehensively investigated.

Fluorescent perylene derivative functionalized titanium oxide gel for sensitive and portable ascorbic acid detection

A fluorescent inorganic titanium oxide gel sensor was prepared from perylene diimide functionalized composite materials, and applied for sensitive and portable ascorbic acid detection.

Tuning the formation of reductive species of perylene-bisimide derivatives in DMF via aggregation matter

Host-guest interaction and chemical modification are found to be effective in tuning the formation of reductive species of perylene-bisimide (PBI) derivatives in DMF. Moreover, some of the PBI derivatives as synthesized produce radical anions in the solvent without the need of a base.

Discrimination of saturated alkanes and relevant volatile compounds via the utilization of a conceptual fluorescent sensor array based on organoboron-containing polymers

A conceptual sensor array for the efficient discrimination and fast detection of saturated alkanes and commonly found volatile solvents is reported.

This work reports a conceptual sensor array for the highly discriminative analysis of 20 clinically and environmentally relevant volatile small organic molecules (VSOMs), including saturated alkanes and common solvents, in the air at room temperature. For the construction of the sensor array, a four coordinated, non-planar mono-boron complex and four relevant polymers are synthesized. Based on the polymers and the use of different substrates, 8 fluorescent films have been fabricated. Integration of the film-based sensors results in the sensor array, which demonstrates unprecedented discriminating capability toward the VSOMs. Moreover, for the signal molecule of lung cancer, n-pentane, the response time is less than 1 s, the experimental detection limit is lower than 3.7 ppm, and after repeating the tests over 50 times no observable degradation was observed. The superior sensing performance is partially ascribed to the tetrahedral structure of the boron centers in the polymers as it may produce molecular channels in the films, which are a necessity for fast and reversible sensing. In addition, the polarity of the micro-channels may endow the films with additional selectivity towards the analytes. The design as demonstrated provides an effective strategy to improve the sensing performance of fluorescent films to very challenging analytes, such as saturated alkanes.

Dynamic covalent bonding-triggered supramolecular gelation derived from tetrahydroxy-bisurea derivatives

A new class of bisurea derivatives bearing tetrahydroxy groups have been proven to be non-gelators in water and various organic solvents even under long-term sonication or efficient heating treatment. We found that it is possible to trigger physical gelation behaviour by constructing dynamic covalent bonding. The results show that formation of dynamic covalent bonding between the borate anion and ethanediol substituent in these bisurea derivatives brings about rapid physical gelation at ambient temperature in a mixture of DMSO and water. During dynamic covalent bonding-triggered gelation, the stepgrowth polymerization from the B-O bonds would increase the size of the molecules and reduce the entropy of mixing as well as facilitate ion-dipole interactions in the linear polymeric gelators. They would drive a self-assembly transition and boost the construction of gel networks in coordination with α-tape urea-urea hydrogen bonding. The gelation mechanism was explored by ¹H NMR, FTIR and rheology techniques. Moreover, the resulting gels are transparent and thixotropic, and could be turned into the sol state under CO₂ or water-stimulus. Furthermore, they are stable in the presence of HAuCl₄ and alkali. Therefore, they would afford another new medium for the growth of Au nanocrystals via in situ reduction and a new sensing medium for detecting Hg²⁺ ions.

Naphthalimide-Based Fluorophore for Soft Anionic Interface Monitoring

A naphthalimide-based low-molecular-mass fluorophore (NA) was designed and synthesized by introducing an azetidine unit onto the aromatic ring of the compound as an electron-donating structure, and a hydrophilic (2-(2-aminoethyl-amino)ethanol) moiety into the "N-imide site" of the core structure. UV-vis absorption and fluorescence measurements revealed that the fluorophore is soluble in water and shows a fluorescent quantum yield of ∼20% and lifetime of ∼3.7 ns in the solvent within a wide pH range. Moreover, the fluorescence emission and anisotropy of the fluorophore as produced are both dependent upon the viscosity and polarity of the medium. Further studies demonstrated that NA can be used as a selective probe to monitor the aggregation of anionic surfactants owing to its accumulation onto the anionic surfaces of the aggregates as formed. Inspired by the discovery, NA was successfully applied for detection of cell membranes and E. coli via monitoring of their negatively charged surfaces, which is important for fast checking of biological contamination of water. Importantly, all the tests could be performed in a visualized manner. We believe that the new, low-molecular-mass fluorophore as created may find applications in chemical and biochemical sensing and imaging.

Molecular Gels as Intermediates in the Synthesis of Porous Materials and Fluorescent Films: Concepts and Applications

Low-molecular-mass organic gelator (LMOG)-based molecular gels are known as one of the most attractive soft materials and have received great attention since the early 1990s. In the last few decades, many LMOGs have been synthesized, and a series of theories have been proposed to better understand molecular gels. However, only limited applications of LMOGs have been realized for a variety of reasons, such as their lack of stability compared to chemical gels. Therefore, efforts to explore the applications of these materials are especially meaningful. As an example, this feature article mainly introduces studies on the application of LMOGs as intermediates in porous materials and fluorescent sensing films. Particular attention will be paid to gelator design, LMOG emulsion preparation, solid surface modification, and the practical application of the obtained materials. Concepts that are related to these studies, such as organic gel-water interface equilibria and molecular gel strategies, will be comprehensively illustrated. Finally, we will conclude with a study of LMOG-based intermediates. Some challenges and future perspectives related to these research areas will also be presented. It is anticipated that this feature article will not only contribute to the further understanding of LMOG-based intermediates but also will help to promote the practical application of molecular gels and facilitate development in related research areas.

Amphiphilic oligoamides as versatile, acid-responsive gelators

Among six oligoamides, G1–G6, G2 stands out as a versatile gelator to form stable hydrogels as well as several organogels. The hydrogel of G2 is able to encapsulate and release medicinally important substances with acid-responsiveness.

Langmuir–Blodgett films of perylene bisimide derivatives and fluorescent recognition of diamines

A fluorescent film was constructed with the well-known Langmuir–Blodgett technique, and it showed exceptional sensing performances for some diamine vapors.