Rapid and Visual Detection of Volatile Amines Based on Their Gas-Solid Reaction with Tetrachloro-p-Benzoquinone

The detection of volatile amines is necessary due to the serious toxicity hazards they pose to human skin, respiratory systems, and nervous systems. However, traditional amines detection methods require bulky equipment, high costs, and complex measurements. Herein, we report a new simple, rapid, convenient, and visual method for the detection of volatile amines based on the gas-solid reactions of tetrachloro-p-benzoquinone (TCBQ) and volatile amines. The gas-solid reactions of TCBQ with a variety of volatile amines showed a visually distinct color in a time-dependent manner. Moreover, TCBQ can be easily fabricated into simple and flexible rapid test strips for detecting and distinguishing n-propylamine from other volatile amines, including ethylamine, n-butyamine, n-pentamine, n-butyamine and dimethylamine, in less than 3 s without any equipment assistance.

Quinoline-cored Poly(Aryl Ether) Dendritic Organogels with Multiple Stimuli-Responsive and Adsorptive Properties

Functional supramolecular gel materials have potential applications in sensors, optical switches, artificial antennae, drug delivery and so on. In this paper, quinoline-cored poly(aryl ether) dendritic organogelators were designed, synthesized and fully characterized. The gelation behaviour of the dendritic organogelator was tested in organic solvents, mixed solvents and ionic liquids. The dendron Q-G1 was found to be an efficient and versatile organogelator toward various apolar and polar organic solvents with the critical gelation concentrations (CGCs) approaching 1.2×10^-2  mol/L, indicating one dendritic organogelator could immobilize 1.2×10³ solvent molecules in the organogel network. Interestingly, these dendrons exhibited excellent gel formation in ionic liquids. Notably, these dendritic organogels were found to display multiple stimuli-responsive properties toward external stimuli including heat, ultrasound and shear stress, with a reversible sol-gel phase transition. In addition, the dendritic organogel could effectively adsorb heavy metals and organic dyes. The removal rate of Pb²⁺ was up to 20% and the adsorption rate for Rhodamine B was as high as 89%.

A stimuli-responsive pillar[5]arene-based hybrid material with enhanced tunable multicolor luminescence and ion-sensing ability

Tunable luminescent materials are becoming more and more important owing to their broad application potential in various fields. Here we construct a pillar[5]arene-based hybrid material with stimuli-responsive luminescent properties and ion-sensing abilities from a pyridine-modified conjugated pillar[5]arene and a planar chromophore oligo(phenylenevinylene) upon coordination of Cd (II) metal cores. This new material not only shows an optimized luminescence due to the minimized π-π stacking and efficient charge transfer properties benefitting from the existence of pillar[5]arene rings, but also exhibits tunable multicolor emission induced by different external stimuli including solvent, ions and acid, indicating great application potential as a fluorescent sensory material, especially for Fe3+. With this pillar[5]arene-based dual-ligand hybrid material, valid optimization and regulation on the fluorescence of the original chromophore have been achieved, which demonstrates a plausible strategy for the design of tunable solid-state luminescent materials and also a prototypical model for the effective regulation of fluorescent properties of planar π systems using synthetic macrocycle-based building blocks.

A reaction-based sensing scheme for volatile organic amine reagents with the chromophoric-fluorogenic dual mode

In this study, we present the classical Michael's addition reaction-based sensing scheme for volatile organic amine reagents such as ethylenediamine, N, N-dimethylethylenediamine and diethylenetriamine using a near-infrared fluorescent dye TCF1. Obvious spectral changes in the UV-vis absorption and fluorescence spectra of TCF1 were observed upon addition of these amine reagents with an effective catalyst DBU, resulting in significant and fast color changes detectable by the naked-eye. TCF1 showed an efficient response to these amine reagents with a low detection limit, especially for diethylenetriamine. NMR and MS spectral analysis proved that the mechanism of the detection was based on the classical Michael addition, which was also verified by the theoretical calculations. In addition, a portable test paper incorporated with TCF1 had also successfully realized the detection of a low concentration of these amine reagents.

Molecular motifs encoding self-assembly of peptide fibers into molecular gels

Peptides are a promising class of gelators, due to their structural simplicity, biocompatibility and versatility. Peptides were synthesized based on four amino acids: leucine, phenylalanine, tyrosine and tryptophan. These peptide gelators, with systematic structural variances in side chain structure and chain length, were investigated using Hansen solubility parameters to clarify molecular features that promote gelation in a wide array of solvents. It is of utmost importance to combine both changes to structural motifs and solvent in simultaneous studies to obtain a global perspective of molecular gelation. It was found that cyclization of symmetric dipeptides, into 2,5-diketopiperazines, drastically altered the gelation ability of the dipeptides. C-l-LL and C-l-YY, which are among the smallest peptide LMOGs reported to date, are robust gelators with a large radius of gelation (13.44 MPa^1/2 and 13.90 MPa^1/2, respectively), and even outperformed l-FF (5.61 MPa^1/2). Interestingly, both linear dipeptides (l-FF and l-LL) gelled similar solvents, yet when cyclized only cyclo-dityrosine was a robust gelator, while cyclo-diphenylalanine was not. Changes in the side chains drastically affected the crystal morphology of the resultant gels. Symmetric cyclo dipeptides of leucine and tyrosine were capable of forming extremely high aspect ratio fibers in numerous solvents, which represent new molecular motifs capable of driving self-assembly.

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.

Visible light-triggered gel-to-sol transition in halogen-bond-based supramolecules

Photoresponsive supramolecular gels have aroused continuous attention because of their extensive applications; however, most studies utilize UV light, which inevitably brings about some health and environmental issues. The halogen bond is an important driving force for constructing supramolecules due to its high directionality, tunable strength, good hydrophobicity, and large size of the halogen atoms. Yet, it still remains a formidable challenge to utilize halogen bonds as a driving force to fabricate a visible light responsive gel. In this work, to fabricate such a gel, azopyridine-containing Azopy-C_n (n = 8, 10, 12) was selected as a halogen bond acceptor, while 1,2-bis(2,3,5,6-tetrafluoro-4-iodophenyl)diazene (BTFIPD) was chosen as both the halogen bond donor and visible light responsive moiety. The visible light response of BTFIPD resulted from the significant separation of n-π* energy levels between trans and cis isomers due to the introduction of an electron-withdrawing group (fluorine) to azobenzene at the ortho-position. Interestingly, the gel exhibited a good gel-to-sol transition behavior upon green light irradiation. At the same time, the morphologies varied from uniform narrow flakes to broad sheets with increasing illumination time. We provide an environmentally-friendly visible light-triggered method to regulate the phase transition of supramolecular materials in applications ranging from energy conversion to information storage.

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.

Norbornene chaotropic salts as low molecular mass ionic organogelators (LMIOGs)

Phenylalanine functionalised norbornene (9:Na) functions as a potent, low molecular-mass (MW = 333 Da) ionic organogelator with a minimum gelating concentration of 0.5 wt% in THF, i-PrOH, 1,4-dioxane and n-BuOH. Fibrous crystals form in the gel and X-ray crystallography identified a cation mediated helical assembly process controlled by the chirality of the phenylalanine. In addition to excellent gelating properties 9:Na readily forms aqueous biphasic and triphasic systems.

AIEE Active Donor-Acceptor-Donor-Based Hexaphenylbenzene Probe for Recognition of Aliphatic and Aromatic Amines

In the present investigation, an intramolecular charge transfer (ICT) and aggregation induced emission enhancement (AIEE) active donor-acceptor-donor (D-A-D) system 5 having fumaronitrile as the acceptor and hexaphenylbenzene (HPB) as the donor moieties joined through rotatable phenyl rings has been designed and synthesized that is highly emissive in the solid state and exhibits stimuli-responsive reversible piezochromic behavior upon grinding and heating. Because of its AIEE characteristics, HPB derivative 5 undergoes aggregation to form fluorescent aggregates in mixed aqueous media that exhibit ratiometric fluorescence response toward aliphatic amines (primary/secondary/tertiary) and turn-off response toward aromatic amines and hence differentiates between them. Further, the solution-coated portable paper strips of derivative 5 showed pronounced and sensitive response toward aromatic and aliphatic amines with a detection limit in the range of picogram and nanogram level, respectively.

Pyrimidine-containing β-iminoenolate difluoroboron complexes acting as non-traditional π-gelators and mechanofluorochromic dyes

A xerogel-based film based on a mechanofluorochromic dye of a β-iminoenolate difluoroboron complex could detect TFA vapor with high performance.

Detection of gaseous amines with a fluorescent film based on a perylene bisimide-functionalized copolymer

A fluorescent copolymer containing PBI units and hydroxyl-ethyl structures was developed for the fast and sensitive detection of gaseous amines

Ylidenemalononitrile enamine-coated media as fluorescent "turn-on" probes for volatile primary amines

Two ylidenemalononitrile enamines, adsorbed to various media, undergo a cyclization reaction with primary amine vapors resulting in a fluorometric and colorimetric response. After determining the media with the fastest response rate for emission "turn-on" to be aluminum oxide activated neutral (AON), we further demonstrate the sensitivity (propylamine concentrations as low as 200 ppm are detected) and selectivity to various analytes including amines, methanol, and ethanethiol. Lastly, as an alternative means of detection, the colorimetric response dye on glass filter paper was shown to detect propylamine concentrations as low as 29 ppm.

Co-assembly of donor and acceptor towards organogels tuned by charge transfer interaction strength

Co-assembly of n-type semiconductors NDI and PDI with p-type pyrene derivatives resulted in the formation of stable organogels, which was induced by the strong charge transfer (CT) interactions between acceptors and donors in chloroform. The dimension size of the aromatic core from the acceptors was found to have a significant impact on the organogels. The width of the fibers from CT gels with NDI is about twice that from gels with PDI. It was found that the acceptor NDI preferred an alternate stacking with donors, intercalated with each other via CT interactions. In contrast, the acceptor PDI preferred to stack among themselves within the assemblies and this arose from the stronger π-π interactions because they had larger aromatic cores than the acceptor NDI. The dimension size of the aromatic core has been proved to have a significant impact on the organogels. The substituent impact of the donors was also studied.

Cyclodextrin-Assisted Two-Component Sonogel for Visual Humidity Sensing

In this work, two naphthalimide-based compounds, 1a and 1b, have been designed and synthesized. Both compounds can form stable two-component gels in n-propanol or n-butanol upon addition of α-cyclodextrin (α-CD) followed by sonication at room temperature. Interestingly, the 1a/α-CD gel is thixotropic and very sensitive to water. Addition of a small amount of water induces rapid gel collapse, allowing further development of the gel as a visual relative humidity sensor. Specificity of the sensor has been confirmed using several approaches, such as scanning electron microscopy and fluorescence, Fourier transform infrared, and ¹H NMR spectroscopy experiments. The results show that α-CD acts as a junction for the assembly of 1a or 1b through hydrogen bonding between hydroxyl and amide groups. Upon addition of water, α-CD interacts with the adamantane group of 1a via an incomplete host-guest encapsulation, resulting in the dissociation of the hydrogen-bonding-assisted two-component assembly, accompanied by gel collapse.

Discrimination of alkyl and aromatic amine vapors using TTF–TCNQ based chemiresistive sensors

Chemiresistors based on TTF–TCNQ microfibers can discriminate alkyl and aromatic amine vapors through the dramatic difference in signal recovery kinetics.

An efficient iodide ion chemosensor and a rewritable dual-channel security display material based on an ion responsive supramolecular gel

The ion stimuli-responsive metallogel PbG could act as a highly selective and sensitive I⁻ sensor and a rewritable dual-channel security display material.

Carbazole modified salicylaldimines and their difluoroboron complexes: effect of the tert-butyl and trifluoromethyl terminal groups on organogelation and piezofluorochromism

Luminescent nanofibers were generated from nontraditional π-gelators based on salicylaldimines and their difluoroboron complex bearing tert-butyl carbazole and trifluoromethylbenzene.

Low molecular weight gels: potential in remediation of crude oil spillage and recovery

A molecular gelator which has strong gelation ability for different crude oils (light to heavy crudes), and a wide range of refinery products is reported for the first time for its potential application in oil spillage/recovery.

Hydrothermal Synthesis of Silver Vanadium Oxide (Ag0.35V2O5) Nanobelts for Sensing Amines

A simple hydrothermal method for the synthesis of Ag0.35V2O5 nanobelts with the assistance of sodium dodecyl sulfate (SDS) is reported in this study. The experimental variables that may affect the nanoparticle structures were investigated. And several advanced techniques, such as TEM, HRTEM, X-ray diffraction (XRD), were used to characterize the morphology and composition of the as-prepared nanobelts. The mechanism of the formation and growth of Ag0.35V2O5 nanobelts was also investigated and discussed. The results show that SDS, as a weak reducing agent, plays a crucial role in the formation of Ag0.35V2O5. According to N2 sorption isothermals, the as-prepared Ag0.35V2O5 nanobelts are found to exhibit relative high surface area. The gas sensing performance of the Ag0.35V2O5 nanobelts towards organic amine was tested. It is found that the nanobelts show superior sensitivity of amine(s) to V2O5 particles, lower detection limit (5 ppm), and higher selectivity of amine versus ammonia at an optimized working temperature of ~260 °C. Moreover, the density functional theory (DFT) simulation was conducted to better understand the sensing mechanism. These findings may be useful in designing promising materials to detect amine gases for medical or food industrial applications.

Tuning soft nanostructures in self-assembled supramolecular gels: from morphology control to morphology-dependent functions

Supramolecular gels are one kind of important soft material, in which small low-molecular weight compounds self-assemble into various nanostructures through non-covalent interactions to immobilize the solvents. While there are many important fundamental issues related to the gelation process, such as the design of the gelator, synergism of various non-covalent interactions between gelators, gelator-solvents, the balances between gelation and crystallization and so on, the self-assembled nanostructures forming during gelation are very interesting. These nanostructures have many unique features, such as the flexibility to respond to external stimuli, morphological diversity, ease of fabrication in large quantities, and so on. This review highlights some important features in tuning the nanostructures in the supramolecular gels from their morphological diversity, morphology control, morphology conversion, and morphology-depended functions.

Photocurrent generation of nanofibers constructed using a complex of a gelator and a fullerene derivative

Two-component xerogel film constructed by a carboxylic acid derivative and fullerene derivative could generate large photocurrent under light irradiation.

Reversible and “fingerprint” fluorescence differentiation of organic amine vapours using a single conjugated polymer probe

By embedding multiple reactive groups onto one polymer, an ultrasensitive and reversible fluorescent probe for different organic amines vapour has been reported.

Emission enhanced two-component gels for the detection of organic amine vapors

A two-component gelator with enhanced emission could be used to quantitatively detect and discriminate between aliphatic and aromatic organic amine vapors.

Nanofibers of hydrogen-bonded two-component gel with closely connected p- and n-channels and photoinduced electron transfer

An D-A-D gelator (DTCQ) was designed and synthesized using 2,3-dimethyl-5,8-di(thiophen-2-yl)quinoxaline and N-alkyl 3-aminocarbazole units as acceptor and donor, respectively, which were linked by a single bond. The compound could gelate several solvents, such as benzyl alcohol, aniline, acetophenone, and o-dichlorobenzene, as well as self-assemble into one-dimensional (1D) nanofibers in gel phase. The absorption and infrared spectra of the gels indicated that π-π interactions between aromatic moieties, intermolecular hydrogen bonds between amide units, and van der Waals forces were the driving forces for the formation of 1D self-assemblies and gel. DTCQ gel was red and emits red fluorescence because it has a strong absorption band at 487 nm and an emissive band at 620 nm. Moreover, DTCQ and a fullerene carboxylic acid formed two-component gel, in which the two compounds developed a hydrogen bond complex and self-assembled into 1D nanofibers with closely connected p- and n-channels. The nanofibrous xerogel film can rapidly generate a photocurrent under visible-light radiation through electron transfer from the gelator to fullerene, and then, the excellent exciton separation and charge transfer to two electrodes.

Response of strongly fluorescent carbazole-based benzoxazole derivatives to external force and acidic vapors

The nanofibers have enhanced emission and exhibited an isothermal reversible mechanochromism. Furthermore, acetic acid vapor may selectively act as stabilizer and developer to retain the information imparted by mechanical force.