Stimuli-Responsive Electrospun Fluorescent Fibers Augmented with Aggregation-Induced Emission (AIE) for Smart Applications

Regioregular Poly(p-phenylene iminoborane): A Strictly Alternating BN-Isostere of Poly(p-phenylene vinylene) with Stimuli-Responsive Behavior

Incorporation of BN units into π-conjugated organic compounds, as substitutes for specific CC couples, often leads to new hybrid materials with modified physical and chemical properties. Poly(p-phenylene iminoborane)s are derived from well-known poly(p-phenylene vinylene) (PPV) by replacement of the vinylene groups by B=N linking units. Herein, an unprecedented poly(p-phenylene iminoborane) is presented that features a strictly alternating sequence of BN units along the main chain. The synthesis thereof was achieved by AB-type polymerization of a monomer featuring an N and a B terminus. Monodisperse oligomers with up to three BN units in the chain were additionally prepared and structurally characterized. Associated with the introduction of a dipole in the regioregular backbone structure, they display notable fluorescence already in solution and large Stokes shifts, distinct from their previously reported BBNN-sequenced congeners. All compounds show aggregation-induced emission enhancement (AIEE) properties. Computational studies provided evidence for emission from either locally excited (LE) or twisted intramolecular charge transfer (TICT) states. These processes can be optionally addressed by various stimuli, giving rise to dual emission, solvatochromic, thermochromic, and reversible mechanochromic behavior.

Aggregation-Induced Emissive Scintillators: A New Frontier for Radiation Detection and Imaging

Aggregation-induced emission (AIE) is a unique phenomenon where certain organic materials exhibit enhanced luminescence in their aggregated states, overcoming the typical quenching observed in conventional organic materials. Since its discovery in 2001, AIE has driven significant advances in fields like OLEDs and biological imaging, earning recognition in fundamental research. However, its application in high-energy radiation detection remains underexplored. Organic scintillators, though widely used, face challenges such as low light yield and poor radiation attenuation. AIE materials offer promising solutions by improving light yield, response speed, and radiation attenuation. This review summarizes the design strategies behind AIE scintillators and their very recent applications in X-ray, γ-ray, and fast neutron detection. We highlight their advantages in enhancing detection sensitivity, reducing background noise, and achieving high-resolution imaging. By addressing the current challenges, we believe AIE materials will play a pivotal role in advancing future radiation detection and imaging technologies.

Photo-induced time-dependent controllable wettability of dual-responsive multi-functional electrospun MXene/polymer fibers

Switchable wettability potential in smart fibers is of paramount importance in various applications. Light-induced controllable changes in surface wettability have a significant role in this area. Herein, smart waterborne homopolymer, functional copolymer with different polarity and flexibility, and multi-functional terpolymer particles containing a time-dependent dual-responsive acrylated spiropyran, as a polymerizable monomer, were successfully synthesized through eco-friendly single-step emulsifier-free emulsion polymerization. Presence of 10 wt% of butyl acrylate and dimethylaminoethyl methacrylate relative to methylmethacrylate as functional comonomers decreased the Tg of the samples almost 20 ℃ and increased their polarity. The optical properties of the particles were investigated, and the UV-vis and fluorescence spectroscopy results showed that not only polarity and flexibility of the polymer chains may have a positive effect on improving the optical properties, but also the simultaneous presence of functional groups has a synergistic effect. The smart polymer particles with flexibility and polarity features exhibited higher absorption and emission compared to other samples. Inspired by these findings, multi-functional smart polymer fibers were prepared using the electrospinning method. The smart multi-functional electrospun fibers containing few-layer Ti3C2 MXenes were synthesized to improve the fibers' properties and change the surface wettability due to the hydrophilic functional groups of MXene. Field-emission scanning electron microscopy images displayed the successful preparation of few-layer MXenes. Smooth and bead-free fibers with bright red fluorescence emission under UV irradiation were shown using fluorescence microscopy. The study on the surface wettability of fibers revealed that UV and visible light irradiation induced reversible time-dependent changes in the wettability of the smart multi-functional MXene/polymer electrospun fibers from hydrophobic to hydrophilic, reaching a water contact angle of 10° from an initial water contact angle of 100° under UV light and also changing to superhydrophilic state with passing time. Upon visible light exposure, the fibers returned to their original state. Furthermore, the fibers demonstrated a high stability over five alternating cycles of UV and visible light irradiation. This study shows that the fabrication of time-dependent smart fibers, utilizing the flexibility and polarity in the presence of MXenes, significantly improves and controls surface wettability changes. The outstanding dynamically photo-switchable wettability of these fibers may offer exciting opportunities in various applications, especially in the separation of oil from water contaminants.

Photoluminescence of Tetra(benzimidazole)phenylethene Derivatives and Their Carbene Metallacycles in Aggregates and Langmuir-Blodgett Films

Molecular structure, external stimuli, and environmental factors all have a strong effect on the internal molecular rotation and vibration of aggregate-induced emission (AIE) luminogens. Here, we report the AIE effect for several newly synthesized amphiphilic tetra(benzimidazole)phenylethene (TBiPE) derivatives and their binuclear N-heterocyclic carbene silver (NHC-Ag) metallacycles in solutions, aggregates, and Langmuir-Blodgett (LB) films. Monolayer behaviors and microscopic images indicate that introducing alkyl chains and binuclear NHC-Ag metallacycles can facilitate the formation of a well-defined insoluble monomolecular layer at the air-water interface. Absorption and luminescence spectral features suggest that both the TBiPEs' cyclization structure and binuclear NHC-Ag metallacycles can provide additional driving forces to restrict the internal molecular motion of the tetraphenylethene (TPE) unit, thus enhancing the AIE effects. Further, external stimuli and environmental factors such as poor solvent addition and LB film deposition also play important roles in the photoluminescent intensity, maximum wavelength, and lifetime. These internal and external factors can result in around 30-40 nm blue-shift for the maximum luminescence wavelength and 2-3 times shorter for the luminescent lifetime. These phenomena can be attributed to the reason that the nonradiative energy transfer efficiency is weakened because of the enhanced hydrophobic interaction and metal-carbene coordination as well as the closely packed arrangement of AIEgens in the LB films; consequently, the radiation energy transfer efficiency increased.

Fine-Scale Aerosol-Jet Printing of Luminescent Metal-Organic Framework Nanosheets

Fabrication of metal-organic framework (MOF) thin films is an ongoing challenge to achieve effective device integration. Inkjet printing has been employed to print various luminescent metal-organic framework (MOF) films. Luminescent metal-organic nanosheets (LMONs), nanometer-thin particles of MOF materials with comparatively large micrometer lateral dimensions, provide an ideal morphology that offers enhancements over analogous MOFs in luminescent properties such as intensity and photoluminescent quantum yield. The morphology is also better suited to the formation of thin films. This work harnesses the preferential features of LMONs to access the advanced technique of aerosol-jet printing (AJP) to print luminescent films with precise geometries and patterns across the micrometer and centimeter length scales. AJP of LMONs exhibiting red (R), green (G), and blue (B) emission were studied systematically to reveal the increase of luminescence upon additive layering printing until a threshold was reached limited by self-quenching. By combining different LMON emitters, emission chromaticity and intensity were shown to be tunable, including the combination of RGB emitters to fabricate white-light-emitting films. A white-light LMON film was printed onto a UV light emitting diode (LED), producing a working white-light-emitting diode. Printing with multiple distinct photoluminescent inks produced intricate multicolor patterns that dynamically responded to excitation wavelength, acting either as micrometer-scale LED-type cells or larger visual tags. Collectively, the work offers an advancement for MOF thin films by printing MON materials using AJP, offering a precise method for manufacturing a wide range of critical functional devices, from luminescent sensors to optoelectronics, and more broadly even the opportunity for printed circuitry with conductive MONs.

Bifunctional In-MOFs for Selective and Sensitive Detection of Trace Nitrobenzene Compounds in Water and Possessing High Proton Conductivity

With the escalating prevalence of terrorism and global environmental pollution, nitroaromatic compounds (NACs) have increasingly come into focus as the primary culprit. To counter these challenges, it is imperative to develop simple and efficient methods for detecting NACs. Considering the electron-deficient structure of NAC molecules, this paper constructed a novel three-dimensional In-MOF with permanent porosity using electron-rich organic molecules 4'-[1,2,2-tris(3',5'-dicarboxy[1,1'-biphenyl]-4-yl)ethenyl]-[1,1'-biphenyl]-3,5-dicarboxylic acid (H8ETTB) for fluorescence detection by photoinduced electron transfer. The results indicated that In-ETTB can sensitively detect trace NACs in water. In-ETTB exhibited the best detection performance for 3-NP, achieving a Ksv value of 8.75 × 104 M-1 with a limit of detection of 0.27 μΜ in aqueous solution; this belongs to a relatively high level among the reported metal organic framework (MOF) materials. Subsequently, anti-interference experiments revealed that In-ETTB exhibits strong specificity fluorescence recognition of NACs, and it could still maintain its structural integrity and fluorescence emission intensity even after 7 cycles of testing. We confirmed that the fluorescence detection of NACs was due to a combined effect of competitive absorption and photoinduced electron transfer through experimental collaboration DFT calculations in detail. Meanwhile, the proton conductivity reached 2.45 × 10-2 S·cm-1 at 98% relative humidity and 90 °C, which is also a high level in MOFs. This work provides a universal method theoretical basis for designing NAC detectors with practical application prospects.

Electrospinning-based sensing technologies: Opportunities for food applications

The article explores the science and practice of electrospinning, tracing its history and examining the factors that influence fiber morphology, including the solution composition, processing conditions, and environmental conditions. It offers a thorough examination of electrospinning fundamentals geared toward generating an appropriate platform for creating tailored nanofibers for sensing applications in the food industry. These nanofibers play a critical role in food analysis, sensing, and traceability, and we highlight their effectiveness in identifying pesticide residues, food components, antibiotics, heavy metals, and foodborne pathogens as well as in monitoring the freshness and spoilage of food. The use of electrospinning technology is poised to make sensing platforms more accessible, affordable, and widespread, thereby significantly contributing to the improvement of food quality and safety monitoring practices.

Grind, shine and detect: mechanochemical synthesis of AIE-active polyaromatic amide and its application as molecular receptor of monovalent anions or nucleotides

A mechanochemical synthesis of novel polyaromatic amide consisting of 1,3,5-triphenylbenzene and 1,1',2,2'-tetraphenylethylene skeletons has been established. The designed mechanochemical approach using readily available and low-cost equipment allowed a twofold increase in reaction yield, a 350-fold reduction in reaction time and a significant reduction in the use of harmful reactants in comparison to the solution synthesis method. The parameters of Green Chemistry were used to highlight the advantages of the developed synthesis method over the solution-based approach. The title compound was found to exhibit attractive optical properties related to the Aggregation-induced emission (AIE) behaviour. Taking the advantage of AIE-active properties of the synthesized polyaromatic amide, its application as effective and versatile molecular receptor towards detection of monovalent anions, as well as bio-relevant anions - nucleotides, has been demonstrated. The values of the binding constants were at the satisfactory level of 104, the detection limit values were low and ranged from 0.2 μM to 19.9 μM.

Textile-Based Adsorption Sensor via Mixed Solvent Dyeing with Aggregation-Induced Emission Dyes

This study demonstrates a novel methodology for developing a textile-based adsorption sensor via mixed solvent dyeing with aggregation-induced emission (AIE) dyes on recycled fabrics. AIE dyes were incorporated into the fabrics using a mixed solvent dyeing method with a co-solvent mixture of H2O and organic solvents. This method imparted unique fluorescence properties to fabrics, altering fluorescence intensity or wavelength based on whether the AIE dye molecules were in an isolated or aggregated state on the fabrics. The precise control of the H2O fraction to organic solvent during dyeing was crucial for influencing fluorescence intensity and sensing characteristics. These dyed fabrics exhibited reactive thermochromic and vaporchromic properties, with changes in fluorescence intensity corresponding to variations in temperature and exposure to volatile organic solvents (VOCs). Their superior characteristics, including a repetitive fluorescence switching property and resistance to photo-bleaching, enhance their practicality across various applications. Consequently, the smart fabrics dyed with AIE dye not only find applications in clothing and fashion design but demonstrate versatility in various fields, extending to sensing temperature, humidity, and hazardous chemicals.

Force-triggered hypso- and bathochromic bidirectional fluorescence switching beyond 120 nm and its anticounterfeiting applications

Achieving high-contrast tricolor emissive regulation of a single-component molecule using a single type of external stimulus is highly desirable but challenging. In the present study, we report a symmetric acceptor-donor-acceptor (A-D-A)-type aggregation-induced emission-active luminogen, which displays a sequential high-contrast fluorescence switching just by anisotropic mechanical grinding. Specifically, upon light grinding, an orange-yellow-to-blue hypsochromic mechanofluorochromic response with a distinct color contrast (change in the maximum emission wavelength, Δλem,max = 122 nm) is noticed, and the slightly ground solid exhibits a blue-to-red high-contrast (Δλem,max = 185 nm) bathochromic mechanofluorochromic conversion upon vigorous grinding. Thus, using a single luminogen developed here, we can realize wide-range (Δλem,max > 100 nm) hypso- and bathochromic fluorescence mechanochromisms simultaneously. The tricolored mechanofluorochromic phenomenon is attributed to two different morphological transitions involving crystalline-to-crystalline and crystalline-to-amorphous states. Furthermore, three information anticounterfeiting systems are developed using the luminogen presented here.

Application of Electrospun Drug-Loaded Nanofibers in Cancer Therapy

In the 21st century, chemotherapy stands as a primary treatment method for prevalent diseases, yet drug resistance remains a pressing challenge. Utilizing electrospinning to support chemotherapy drugs offers sustained and controlled release methods in contrast to oral and implantable drug delivery modes, which enable localized treatment of distinct tumor types. Moreover, the core-sheath structure in electrospinning bears advantages in dual-drug loading: the core and sheath layers can carry different drugs, facilitating collaborative treatment to counter chemotherapy drug resistance. This approach minimizes patient discomfort associated with multiple-drug administration. Electrospun fibers not only transport drugs but can also integrate metal particles and targeted compounds, enabling combinations of chemotherapy with magnetic and heat therapies for comprehensive cancer treatment. This review delves into electrospinning preparation techniques and drug delivery methods tailored to various cancers, foreseeing their promising roles in cancer treatment.

Unlocking Diabetic Acetone Vapor Detection by A Portable Metal-Organic Framework-Based Turn-On Optical Sensor Device

Despite exhaled human breath having enabled noninvasive diabetes diagnosis, selective acetone vapor detection by fluorescence approach in the diabetic range (1.8-3.5 ppm) remains a long-standing challenge. A set of water-resistant luminescent metal-organic framework (MOF)-based composites have been reported for detecting acetone vapor in the diabetic range with a limit of detection of 200 ppb. The luminescent materials possess the ability to selectively detect acetone vapor from a mixture comprising nitrogen, oxygen, carbon dioxide, water vapor, and alcohol vapor, which are prevalent in exhaled breath. It is noteworthy that this is the first luminescent MOF material capable of selectively detecting acetone vapor in the diabetic range via a turn-on mechanism. The material can be reused within a matter of minutes under ambient conditions. Industrially pertinent electrospun luminescent fibers are likewise fabricated alongside various luminescent films for selective detection of ultratrace quantities of acetone vapor present in the air. Ab initio theoretical calculations combined with in situ synchrotron-based dosing studies uncovered the material's remarkable hypersensitivity toward acetone vapor. Finally, a freshly designed prototype fluorescence-based portable optical sensor is utilized as a proof-of-concept for the rapid detection of acetone vapor within the diabetic range.

Photo-Responsive Dynamic Organic Room-Temperature Phosphorescence Materials Based on a Functional Unit Combination Strategy

A rational molecular design strategy facilitates the development of a purely organic room-temperature phosphorescence (RTP) material system with precisely regulated luminescence properties, which surely promotes its functional integration and intelligent application. Here, a functional unit combination strategy is proposed to design novel RTP molecules combining a folding unit with diverse luminescent cores. The different luminescent cores are mainly responsible for tunable RTP properties, while the folding unit contributes to the spin-orbit coupling (SOC) enhancement, which makes the RTP material design as workable as the building block principle. By this strategy, a series of color/lifetime-tunable RTP materials is achieved with unique photo-responsive RTP enhancement when subjected to UV irradiation, which expands their application scenarios in reusable privacy tags, advanced "4D" encryption, and phase separation analysis of blended polymers. This work suggests a simple and effective strategy to design purely organic RTP materials with tunable color and lifetime, and also provides new application options for photo-responsive dynamic RTP materials.

Photo-Controlled Nano-Supramolecular Size and Reversible Luminescent Behaviors Based on Cucurbit[7]uril Cascaded Assembly

Supramolecular luminescent material with switchable behavior and photo-induced aggregation with emission enhancement is a current research hot spot. Herein, a size-tunable nano-supramolecular assembly with reversible photoluminescent behavior was constructed by noncovalent polymerization of diarylethene-bridged bis(coumarin) derivative (DAE-CO), cucurbit[7]uril (CB[7]), and β-cyclodextrin-grafted hyaluronic acid (HACD). Benefiting from the macrocyclic confinement effect, the guest molecule DAE-CO was included into the cavity of CB[7] to give enhanced fluorescence emission of the resulting DAE-CO⊂CB[7]2 with longer lifetime at 432 nm to 1.43 ns, thereby further enhancing fluorescence output and lifetime (1.46 ns) when further assembled with HACD, compared with the free DAE-CO (0.95 ns). In addition, DAE-CO, DAE-CO⊂CB[7]2, and DAE-CO⊂CB[7]2&HACD all possessed characteristics of aggregation-induced emission and reversible photo-switched structural interconversion, exhibiting an obvious photophysical activation phenomenon of self-aggregation into larger nanoparticles with increase in fluorescence emission intensity, lifetime, and size after irradiation, which could be increased step by step with the alternating irradiation of 254 nm (5 min) or >600 nm (30 s) repeated 7 times. These supramolecular assemblies were successfully used in the tumor cells' targeted imaging and anti-counterfeiting because of the capability of HACD for recognizing specific receptors overexpressed on the surface of tumor cells and the excellent photo-regulated switch ability of DAE-CO, providing an approach of constructing photo-induced emission-enhanced luminescent materials.

A Review on 1-D Nanomaterials: Scaling-Up with Gas-Phase Synthesis

Nanowire-like materials exhibit distinctive properties comprising optical polarisation, waveguiding, and hydrophobic channelling, amongst many other useful phenomena. Such 1-D derived anisotropy can be further enhanced by arranging many similar nanowires into a coherent matrix, known as an array superstructure. Manufacture of nanowire arrays can be scaled-up considerably through judicious use of gas-phase methods. Historically, the gas-phase approach however has been extensively used for the bulk and rapid synthesis of isotropic 0-D nanomaterials such as carbon black and silica. The primary goal of this review is to document recent developments, applications, and capabilities in gas-phase synthesis methods of nanowire arrays. Secondly, we elucidate the design and use of the gas-phase synthesis approach; and finally, remaining challenges and needs are addressed to advance this field.

Multistimuli-responsive fluorescence behaviours of aggregation-induced emission small-molecule and electrospun nanofibre films for acid-base vapour sensing

Multistimuli-responsive fluorescent materials have garnered great research interest benefited from their practical applications. Two twisted-structure compounds containing tetraphenylethylene (TPE) as the aggregation-induced emission (AIE) group and a pyridine unit as the acid reaction site to obtain new multistimuli-responsive fluorescent compounds (namely, TPECNPy: TPECNPy-2 and TPECNPy-3) were successfully synthesized through a one-step Knoevenagel condensation reaction. The multiple-stimuli response process of TPECNPy was investigated by means of photoluminescence (PL) spectra and emission colour. The results showed that both TPECNPy compounds with excellent AIE abilities displayed reversible emission wavelength and colour changes in response to multiple external stimuli, including grinding-fuming by CH2 Cl2 or annealing and HCl-NH3 vapour fuming. More importantly, fluorescent nanofibre films were prepared by electrospinning a solution of TPECNPy mixed with cellulose acetate (CA), and these exhibited reversible acid-induced discolouration, even with only 1 wt% TPECNPy. The results of this study may inspire strategies for designing multistimuli-responsive materials and preparing fluorescent sensing nanofibre films.

Monomer Emission Mechanism Research of Tetraphenylethene Derivative with Supramolecular Self-Assembly in Polymer Microspheres

The monomer emission property of the tetraphenylethene (TPE) derivative is rarely reported, and its photoluminescence (PL) mechanism related to supramolecular self-assembly needs further in-depth research. Two long alkyl chain modified derivatives, the TPE derivative (TPE-C10) and pyrene derivative (Pyrene-C10), are designed and synthesized, which possess similar supramolecular assembly behavior but exhibit different PL properties. TPE-C10 not only forms self-assembly morphologies with monomer emission but also emits aggregation-induced emission (AIE). Moreover, the polymer microspheres containing TPE-C10 and Pyrene-C10 are prepared, which can dissolve or swell in different organic solvents. The changed binding effect of polymer chains achieves the luminescence transformation of TPE-C10 from AIE to monomer emission. This work hopefully can enrich luminescent materials based on the monomer emission of the TPE derivative and provide a new method for mechanism studies about supramolecular self-assembly and luminescence.

Low-Pressure Sensitive Piezochromic Fluorescence Switching of Tetraphenylethylene-Anthraquinone

Sensing of low-pressure signals is of great importance for cutting-edge technologies. Organic piezochromic molecules offer a promising library of pressure sensitive materials which can be tailor-designed toward specific requirements. However, very few examples of low-pressure sensitive piezochromic fluorescent molecules have been obtained till date, and the underlying mechanisms are still in its infancy. Herein, we report highly sensitive piezochromic fluorescent switching under low-pressure regimes (∼60 kPa) of tetraphenylethylene-anthraquinone (TPE-AQ) based on the controlled molecular design and polymorphic phase strategy. The influence of both intramolecular conformation effect and variations of intermolecular stacking modes on the piezochromic property of TPE-AQ is investigated. The underlying mechanism of the low-pressure sensitive piezochromic fluorescence switching is demonstrated to be closely related to the loosely packed molecular orientation, as confirmed by X-ray diffraction measurements combined with simulations. This work provides a way to design highly efficient pressure sensors based on organic molecular systems.