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

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.

Recent Advances in Construction Strategies for Fluorescence Sensing Films

A year ago, film-based fluorescent sensors (FFSs) were recognized in the "IUPAC Top Ten Emerging Technologies in Chemistry 2022" due to their extensive application in detecting hidden explosives, illicit drugs, and volatile organic compounds. These sensors offer high sensitivity, specificity, immunity to light scattering, and noninvasiveness. The core of FFSs is the construction of high-performance fluorescent sensing films, which are dependent on the processes of "energy transfer" and "mass transfer" in the active layer and involve complex interactions between sensing molecules and analytes. This Perspective focuses on the latest strategies in constructing these films, emphasizing the design of sensing molecules with various innovative features and structures that enhance the mass transfer efficiency. Additionally, it discusses the ongoing challenges and potential advancements in the field of FFSs.

Recent Advances in the Synthesis of Borinic Acid Derivatives

Borinic acids [R2B(OH)] and their chelate derivatives are a subclass of organoborane compounds used in cross-coupling reactions, catalysis, medicinal chemistry, polymer or optoelectronics materials. In this paper, we review the recent advances in the synthesis of diarylborinic acids and their four-coordinated analogs. The main strategies to build up borinic acids rely either on the addition of organometallic reagents to boranes (B(OR)3, BX3, aminoborane, arylboronic esters) or the reaction of triarylboranes with a ligand (diol, amino alcohol, etc.). After general practical considerations of borinic acids, an overview of the main synthetic methods, their scope and limitations is provided. We also discuss some mechanistic aspects.

Advances in Molecular Design and Photophysical Engineering of Perylene Bisimide-Containing Polyads and Multichromophores for Film-Based Fluorescent Sensors

Film-based fluorescent sensors (FFSs) represent an important chemistry technology for meeting the urgent needs of on-site and real-time analysis, thereby enabling significant applications in environmental and health monitoring. As the core of FFSs, innovative design of sensing fluorophores and their intrinsic excited-state-related response nature endow FFSs with superior sensing performances in an endless expansion. In this Perspective, we specifically focus on perylene bisimide (PBI)-containing polyads and multichromophores with rigid configuration and notable photochemical stability for developing high-performance FFSs. These nonplanar structures mitigate aggregation and create abundant gaps for the sake of mass transfer and availability of the sensing units in the adlayer of the sensing films. We also comprehensively discuss how to adjust electronic coupling governing the excited-state events by appropriate functionalization strategies, thus providing a plethora of valuable insights for the exploration of the structure-property relationships in these orchestrated molecular systems. Throughout this Perspective, we also identify opportunities for FFSs in the future developments.

pH Programmed Optical Sensor Arrays for Cancer Plasma Straightforward Discrimination Based on Protein-Responsive Patterns

Optical cross-reactive sensor arrays inspired by the mammalian olfactory system that can realize straightforward discrimination of plasma from cancer patients hold great potential for point-of-care diseases diagnostics. Herein, a pH programmed fluorescence sensor array based on protein-responsive patterns was designed for straightforward discrimination of different types of cancer plasma. It is worth noting that plasma discrimination can be realized only by programming one nanomaterial using different pH values, which greatly simplifies the programmable design of the sensor array, making it an important highlight of this work. In addition, the mechanism of the pH programmed fluorescence sensor array for protein responsiveness was systematically investigated through molecular docking simulation, fluorescence resonance energy transfer (FRET), and fluorescence lifetime experiments. Most importantly, not only can the differences between plasma from healthy people and and from patients with different cancer species including gastric cancer, liver cancer, breast cancer, and cervical cancer be discriminated by this pH programmed fluorescence sensor array, but also the blind test of unknown plasma samples can be well identified with 100% accuracy, indicating its promising prospect in clinical application.

Film-based fluorescent sensor for visual monitoring and efficient removal of aniline in solutions and gas phase

Aniline has attracted much concern for its long degradation half-life and huge toxicity to the environment and human beings. Therefore, the development of a multi-functional device for visual detection and efficient removal of aniline was highly anticipated. In our work, the small-size Eu@UiO-66(COOH) was obtained by post-synthesis modification (PSM), and then the film-based fluorescent sensor was prepared by crosslinking reaction. The films not only showed incredible mechanical stability and potential for large-scale preparation, but also have excellent fluorescence response to aniline in solutions and gas phase. As the concentration of aniline increased, the fluorescence of films gradually increased at 350 nm, while the fluorescence gradually quenching at 620 nm, and the detection limits (LOD) of aniline in water and air were 0.27 ppb and 0.086 ppb, respectively. In addition, the adsorption performance of the film for aniline has also been confirmed and the maximum adsorption capacity was 32.6 mg/g, which is a strong guarantee for the realization of ultra-trace detection and toxicity reduction of aniline. In summary, the multi-functional film sensor has been designed for ultra-trace detection and efficient removal of aniline in solutions and gas phase, and have significant value for pollutant treatment, ecological restoration and early prevention.

Aminoboranes via Tandem Iodination/Dehydroiodination for One-Pot Borylation

A rapid synthesis of aminoboranes from amine-boranes utilizing an iodination/dehydroiodination sequence is described. Monomeric aminoboranes are generated exclusively from several substrate adducts, following an E2-type elimination, with the added base playing a critical role in monomer vs dimer formation. Diisopropylaminoborane formed using this methodology has been applied to a one-pot palladium-catalyzed conversion of iodo- and bromoarenes to the corresponding boronates. Additionally, modification of the workup allows for isolation of the boronic acid and recovery of the utilized amine.

Recent advances in the synthesis of luminescent tetra-coordinated boron compounds

Tetra-coordinated boron compounds offer a plethora of luminescent materials. Different chelation around the boron center (O,O-, N,C-, N,O-, and N,N-) has been explored to tune the electronic and photophysical properties of tetra-coordinated boron compounds. A number of fascinating molecules with interesting properties such as aggregation induced emission, mechanochromism and tunable emission by changing the solvent polarity were realised. Owing to their rich and unique properties, some of the molecules have shown applications in making optoelectronic devices, probes and so on. This perspective provides an overview of the recent developments of tetra-coordinated boron compounds and their potential applications.

High-Performance NMHC Detection Enabled by a Perylene Bisimide-Cored Metallacycle Complex-Based Fluorescent Film Sensor

Non-methane hydrocarbons (NMHCs) can serve as precursors of ozone and photochemical smog, and hence their highly efficient detection is of great importance for air quality monitoring. Here, we synthesized a new fluorescent perylene bisimide (PBI)-cored metallacycle complex through coordination-driven self-assembly and used it for the production of a fluorescent film sensor. The unique rectangular structure of the developed fluorophore endows the sensor with enhanced sensing performance and discriminability to n-alkanes (C_5-10). Specifically, the experimental detection limits for n-pentane, n-hexane, and n-decane are 39, 7, and 1.4 mg/m³, respectively, and the corresponding linear ranges are from 39 to 2546, 7 to 1745, and 1.4 to 85 mg/m³, respectively. Moreover, the sensing is fully reversible. In tandem with a gas chromatographic separation system, the film sensor showed comparable detection ability for the n-alkanes with a commercial flame ionization detector (FID), while the film sensor needs no hydrogen; it occupies a much smaller size (30 × 30 × 44 mm³) and consumes less energy (0.215 W). Further studies demonstrated that the developed sensor can be used for on-site and real-time quantification of NHMCs, laying the foundation for developing into a portable detector.

Perylene Bisimide-Cored Supramolecular Coordination Complexes: Interplay between Ensembles, Excited State Processes, and Aggregation Behaviors

Manipulating the optical properties of fluorescent species is challenging owing to complicated and tedious synthetic works. Herein, the photophysical properties of perylene bisimide (PBI) were effectively tuned by varying the geometrical arrangement of PBI moieties within supramolecular coordination complexes (SCCs), where a PBI-based dicycle (2) and a trigonal prism (3) were generated via using a typical 90° Pt(II) reagent, cis-(PEt₃ )₂ Pt(OTf)₂ -based coordination-driven self-assembly approach. The ligand, an ortho-tetrapyridiyl-PBI (1), exhibits a moderate fluorescence quantum yield (∼13 %) and efficient inter-system crossing (ISC). 2, however, is much more emissive with a fluorescence quantum yield of ∼41 %, and the relevant ISC process is significantly hindered. The fluorescence quantum yield of 3 is merely ∼6 % due to the observed symmetry-breaking charge separation (SB-CS), which turns to triplet state upon charge recombination. Interestingly, 3 could be fully transformed into 2 by simply adding a suitable amount of a 90° Pt(II)-based neutral triangle. Moreover, 2 tends to form discrete dimers both in crystal and solution states, but 3 does not show the property. Therefore, controlling geometrical arrangement of fluorophores through coordination-driven self-assembly could be taken as another effective way to tune their excited state relaxation pathways and construct high-performance optical molecular materials, which generally have to be prepared via organic synthesis.

A Fluorescence Sensor Array Based on Zinc(II)-Carboxyamidoquinolines: Toward Quantitative Detection of ATP*

The newly prepared fluorescent carboxyamidoquinolines (1-3) and their Zn(II) complexes (Zn@1-Zn@3) were used to bind and sense various phosphate anions utilizing a relay mechanism, in which the Zn(II) ion migrates from the Zn@1-Zn@3 complexes to the phosphate, namely adenosine 5'-triphosphate (ATP) and pyrophosphate (PPi), a process accompanied by a dramatic change in fluorescence. Zn@1-Zn@3 assemblies interact with adenine nucleotide phosphates while displaying an analyte-specific response. This process was investigated using UV-vis, fluorescence, and NMR spectroscopy. It is shown that the different binding selectivity and the corresponding fluorescence response enable differentiation of adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), pyrophosphate (PPi), and phosphate (Pi). The cross-reactive nature of the carboxyamidoquinolines-Zn(II) sensors in conjunction with linear discriminant analysis (LDA) was utilized in a simple fluorescence chemosensor array that allows for the identification of ATP, ADP, PPi, and Pi from 8 other anions including adenosine 5'-monophosphate (AMP) with 100 % correct classification. Furthermore, the support vector machine algorithm, a machine learning method, allowed for highly accurate quantitation of ATP in the range of 5-100 μM concentration in unknown samples with error <2.5 %.

Noninvasive Detection of Ammonia in the Breath of Hemodialysis Patients Using a Highly Sensitive Ammonia Sensor Based on a Polypyrrole/Sulfonated Graphene Nanocomposite

In this work, we fabricated fast-responsive and highly sensitive chemiresistive sensors based on nanocomposites of polypyrrole and graphitic materials such as graphene oxide (GO), reduced graphene oxide (RGO), and sulfonated graphene (SRGO) by an in situ chemical oxidative polymerization method. The synthesized nanocomposites were characterized using field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD). The effects of the operating temperature of different nanocomposites were investigated at four temperatures (28, 40, 50, and 60 °C), and the results were compared with that of the polypyrrole-based sensor. The experimental results for sensors indicate that the proposed PPy/SRGO sensor could be an appropriate choice for NH₃ detection at 28 °C in the range of 0.50 parts per billion (ppb) to 12 parts per million (ppm). The PPy/SRGO nanocomposite gas sensor exhibited fast responsivity, good repeatability, and high chemical selectivity to low-concentration ammonia against humidity, methanol, ethanol, acetone, formaldehyde, dibutylamine, dimethylamine, methylamine, carbon monoxide, and nitrogen oxide at 28 °C. We utilized the PPy/SRGO sensor for studying the variation of the ammonia concentration in hemodialysis (HD) patients' breath before and after dialysis and correlated it with the blood urea nitrogen (BUN) levels. The results of the PPy/SRGO sensor indicated that the breath ammonia concentration significantly decreased after dialysis in agreement with BUN. The results demonstrate the potential application of the PPy/SRGO sensor for noninvasive detection of ammonia in breath and make this type of sensor a promising tool for the diagnosis of renal and liver diseases.

High-Performance Trichloroacetic Acid Sensor Based on the Intramolecular Hydrogen Bond Formation and Disruption of a Specially Designed Fluorescent o-Carborane Derivative in the Film State

Discriminative and sensitive detection of environmentally important and health-related trichloroacetic acid (TCA) suffers from various problems such as bulky instruments and time-consuming operation as well as complex sample processing. Herein, we present a rapid, sensitive, and specific method for the detection of gaseous TCA using a fluorescent single-molecule array. An o-carborane-based benzothiazole derivative (CB-BT-OCH₃) with specific fluorescence properties was specifically designed and utilized to fabricate a film-based single-molecule array. It was revealed that the fluorescent film is photochemically stable and extremely sensitive to TCA vapor, depicting an observable fluorescence color change from green to blue. The experimental detection limit is 0.2 ppm, which is lower than the safety limit (1 ppm) required by the threshold limit values and biological exposure indices. In addition, the film could show detectable intensity change within 0.2 s. On the basis of multiple signal responses, a conceptual two-channel-based fluorescent TCA sensor was developed. Importantly, the proposed conceptual sensor paves a new route to the development of specific fluorescent film-based sensor arrays with a single fluorophore as sensing units.

High-Performance Ketone Sensing in Vapor Phase Enabled by o-Carborane-Modified Cyclometalated Alkynyl-Gold(III) Complex-Based Fluorescent Films

Development of high-performance, low-power-consumption, small-sized detectors is a key issue for fabricating specific miniaturized chromatographs (GCs). Herein, we report, for the first-time, utilization of a film-based fluorescent sensor as a GC detector. In the studies, we designed a new o-carborane derivative of a known cyclometalated alkynyl-gold(III) complex, Au-CB. Unlike the parent gold(III) complex, the newly synthesized Au-CB depicted a remarkable aggregation-induced emission (AIE) property, enabling fabrication of a fluorescent film. The film emission is highly sensitive to the presence of ketones such as acetone, 2-pentanone, 3-pentanone, cyclopentanone, etc., in the air. It was demonstrated that the sensing performance of the film could be further improved by changing the film from a planar structure to a tubular one. Via combination with an earlier reported homemade sensory device, a conceptual film-based fluorescent sensor was developed, which demonstrated instant and fully reversible response to the ketones. The experimental detection limits for cyclohexanone and acetone could be lower than 0.08 and 13.0 ppm, respectively. Moreover, the sensor is super stable, as 24 h continuous illumination resulted in less than 1.0% reduction of the fluorescence emission, 50 successive sensings showed no observable decay in the performance, and more than 1 year of storage had no effect upon the property. Further studies demonstrated that the film sensor could be used as a GC detector with performance comparable to the commercial flame ionization detector (FID), which lays the foundation for future applications in specific miniaturized GCs because of its merits in size, power consumption, carrier gas, etc.

Supramolecular architectures sustained by delocalised C–I⋯π(arene) interactions in molecular crystals and the propensity of their formation

A survey of delocalised C–I⋯π(chelate ring) interactions is presented.

Spacer group-controlled luminescence and response of C3-symmetric triphenylamine derivatives towards force stimuli

Spacer groups have the ability to regulate the responses of two C₃-symmetric triphenylamine derivatives. Double bonds induced larger spectral shifts compared to that of single bonds.

A colorimetric sensor array for the discrimination of Chinese liquors

Although some colorimetric sensor arrays have been developed for the identification of Chinese liquors, they usually require the confirmation of volatile markers in the liquors by chromatography and mass spectrometry firstly. Herein, we present a simple colorimetric sensor array to identify various Chinese liquors in the liquid phase without the aid of other analytical techniques. The colorimetric sensor array consists of six commercially available and inexpensive solvatochromic dyes, and the sensing mechanism of this array is based on the response of solvatochromic dyes to their local polarity. On the basis of the colour changes of the sensor array, different Chinese liquors are discerned readily using pattern recognition methods, and the statistical analysis results (i.e., hierarchical clustering analysis and principal component analysis) reveal that the as-fabricated sensor array can distinguish the subtle differences between different liquors from the same winery and the same flavor type. Moreover, the developed sensor array can even distinguish diverse diluted liquors from the pristine ones.

Perylene Bisimide Derivative-Based Fluorescent Film Sensors: From Sensory Materials to Device Fabrication

Film-based fluorescent sensors have become an important field of sensor research due to abundant acquirable signals, real-time monitoring, and ease of miniaturization and integration, where chemically sensitive films are the most vital component of the sensor devices. In this feature article, we introduce hardware structures of film-based fluorescent sensors following the examination/investigation of the recent progress of such sensors with perylene bisimide (PBI) derivatives as sensing fluorophores in the films. PBI derivatives were specially chosen because of their outstanding chemical, photochemical, and thermal stabilities as well as their unusual high-fluorescence quantum yields. And finally, we provide a prediction for the future developments and challenges of this emerging field.

Water-soluble carbon dots with blue, yellow and red emissions: mechanism investigation and array-based fast sensing application

This work prepared three kinds of CDs with blue, yellow and red emissions and further in-depth investigated their luminescence mechanisms through theoretical calculations together with experimental data. Afterwards, a sensor array by using these CDs for fast discriminating different types of sulfur-containing species was constructed.

Aggregation-induced emission based one-step “lighting up” sensor array for rapid protein identification

Based on the distinct fingerprint-like fluorescence responses generated by different electrostatic and hydrophobic interactions, a “lighting up” aggregation-induced emission (AIE) sensor array was developed for rapid protein discrimination.

Development of a Column-Shaped Fluorometric Sensor Array and Its Application in Visual Discrimination of Alcohols from Vapor Phase

Portable, miniaturized, and inexpensive detectors are in high demand for detecting and discriminating volatile organic compounds (VOCs). Sensor array design and exploitation are two key issues for new detector development. In contrast to the most reported plane-shaped sensor array for gaseous analyte sensing, here we report a column-shaped fluorometric sensor array by using fluorophore-loaded silica particles (∼40 μm) filled capillary. In the design, the capillary serves as test chamber and facilitates visualization. The orifices of the capillary were used as inlet and outlet for gaseous analyte. Sensing modules are installed in series, which lays foundation for their even and effective contact with the gaseous analyte. Meanwhile, further capsulation could be avoided. Silica particles were chosen as carries due to their preferred adsorption behavior to VOCs. By choosing four typical fluorophores (PBI-CB, Py-CB-Ph, Py-At, and NA-Ch) as sensing units, a 4-element fluorometric sensor array was achieved. Fluorescence of the array varied when different alcohol vapors were pumped in. The six tested alcohols could not only be distinguished as primary, secondary, or tertiary, but also be identified individually. The array had good reproducibility in visualization of the six alcohols. In addition, the orders of the fluorophores can be changed as desired. It is believed that the proofed concept provides not only a totally new design of sensor array but also contributes a new strategy for the discrimination of the alcohols as examined.

Single-Benzene-Based Solvatochromic Chromophores: Color-Tunable and Bright Fluorescence in the Solid and Solution States

The search for structurally simple chromophores with superior fluorescence brightness and a wide range of solvent compatibility is highly desirable. Herein, a new type of single-benzene-based solvatochromic chromophore with a symmetric bifunctional structure, in which azetidine and ethoxycarbonyl moieties serve as the electron-donating and -withdrawing groups, respectively, is reported. This chromophore exhibits an extraordinary wide range of solvent compatibility and preserves excellent fluorescence quantum yields from nonpolar n-hexane to polar methanol and even in water. Unusually, the symmetric structure of the chromophore shows a distinct color change from bright green to red with increasing solvent polarity and possesses large Stokes shifts (λ=132-207 nm) in the tested solvents. Moreover, this single-benzene-based chromophore displays good photochemical stability in both solution and solid states, and even exhibits reversible mechanochromic luminescence.

Film-based fluorescence sensing: a "chemical nose" for nicotine

A novel series of emissive o-carborane derivatives, which showed multicolor, highly solid-state emission (ΦF ≥ 43%) and ideal photochemical stability, were synthesized. Inspired by the powerful mammalian olfactory system, we, for the first time, successfully obtained a fluorescent sensor array, which exhibits superior detection capability for nicotine in the gaseous phase (down to 3 ppb). Furthermore, the sensor array can be extended to detect nicotine in aqueous solution at the nano-gram level (∼0.1 ng cm-2) and determine the smoke of cigarette and electronic cigarette.

Naphthyl End-Capped Terthiophene-Based Chemiresistive Sensors for Biogenic Amine Detection and Meat Spoilage Monitoring

A reliable and sensitive detection of biogenic amines (BAs) is essential to ensure food safety and maintain public health. In this study, two naphthyl end-capped terthiophene derivatives, namely, 5-(naphthalen-1-yl)-2,2':5',2''-terthiophene (NA-3T) and 5,5''-di(naphthalen-1-yl)-2,2':5',2''-terthiophene (NA-3T-NA), were employed to develop chemiresistive sensors for detecting gaseous BAs. In contrast to NA-3T, the NA-3T-NA-based sensor showed a higher sensitivity for trimethylamine (TMA) with an experimental detection limit lower than 22 ppm, and for aromatic BAs, including dopamine, histamine, tryptamine, and tyramine. Additionally, the recovery time for TMA was found to be shorter than 23 s. In addition, both sensors were successfully used for an in situ evaluation of meat freshness by monitoring the concentration of relevant volatile BAs. The difference in the sensing performances of the two chemiresistive sensors was tentatively ascribed to different packing structures of the derivatives and the adlayer structures of the films developed with the compounds.

Poly(ionic liquid)s as a distinct receptor material to create a highly-integrated sensing platform for efficiently identifying numerous saccharides

A highly-integrated sphere-based sensing platform for directly identifying numerous saccharides very efficiently is developed.

Saccharides have strong hydrophilicities, and are complex molecular structures with subtle structure differences, and tremendous structural variations. The creation of one sensing platform capable of efficiently identifying such target systems presents a huge challenge. Using the integration of unique multiple noncovalent interactions simultaneously occurring in poly(ionic liquid)s (PILs) with multiple signaling channels, in this research an aggregation-induced emission (AIE)-doped photonic structured PIL sphere is constructed. It is found that such a sphere can serve as a highly integrated platform to provide abundant fingerprints for directly sensing numerous saccharides with an unprecedented efficiency. As a demonstration, 23 saccharides can be conveniently identified using only one sphere. More importantly, by using simple ion-exchanges of PIL receptors or/and increasing the AIE signaling channels, this platform is able to perform, on demand, different sensing tasks very efficiently. This is demonstrated by using it for the detection of difficult targets, such as greatly extended saccharides as well as mixed targets, in real-life examples on one or two spheres. The findings show that this new class of platform is very promising for addressing the challenges of identifying saccharides.

Mechanochromic Wide-Spectrum Luminescence Based on a Monoboron Complex

A reversible mechanochromic luminescent material based on a simple tetrahedral monoboron complex (B-1) is described. Interestingly, in addition to amorphous powders (P), the compound could exist in three unique crystal states (A, B, and C), showing efficient green-to-red luminescent colors, which is a result of wane and wax of dual emissions of the compound. Surprisingly, one of the emissions increases significantly with increasing temperature, fully offsetting the quenching effect of temperature-assisted internal conversion process. The four states are fully interconvertible through grinding and heating, allowing color writing/painting with a single ink.

Coordination-Driven Self-Assembled Metallacycles Incorporating Pyrene: Fluorescence Mutability, Tunability, and Aromatic Amine Sensing

Constructing polycyclic aromatics-based, highly emissive fluorophores with good solubility and tunable aggregated structures and properties is of great importance for film fabrication, solution processing, and relevant functionality studies. Herein, we describe a general strategy to endow conventional organic fluorophores with enhanced solubility and modulated fluorescent properties via their incorporation into coordination-driven self-assembled metallacycles. A widely used fluorophore, pyrene, was decorated with two pyridyl groups to yield functionalized pyrene 4. Mixing 4 with three aromatic dicarboxylates with different lengths and a 90° Pt(II) metal acceptor in a 2:2:4 stoichiometric ratio resulted in the formation of three metallacycles, 1, 2, and 3. The metallacycles display good solubility in polar organic solvents, highly aggregation-dependent fluorescence, and size-dependent emissions at higher concentrations. Moreover, metallacycle 2-based, silica-gel-supported film as fabricated not only is more emissive than the ligand 4-based one but also displays much improved sensing properties for amines in the vapor state, as demonstrated by significantly increased response speed and decreased recovery time. The enhanced solubility, unique fluorescence behavior, and multi-factor modulation character show that coordination-driven self-assembly can be utilized for the development of new fluorophores through simple modification of conventional fluorophores. The fluorophores synthesized this way possess not only complex topological structures but also good modularity and tunability in fluorescence behavior, which are important for grafting multi-stage energy-transfer systems necessary for the development of high-performance sensing materials.

Ultrafast and Efficient Detection of Formaldehyde in Aqueous Solutions Using Chitosan-based Fluorescent Polymers

Detection of a toxic formaldehyde (HCHO) pollutant in aqueous solutions is of significant importance, because HCHO is widely found in aquatic food because of illicit addition or improper storage. Many small-molecule-based fluorescent probes, which rely on HCHO-specific formaldehyde-amine condensation or the aza-Cope rearrangement reaction, have been developed in terms of facile operation and high selectivity. However, some primary challenging issues are the restricted sensitivity and long equilibrium response time caused by the slow chemical reaction between these small-molecule-based sensors and low-concentration HCHO pollutant in testing samples. Herein, a robust hydrophilic hydrazino-naphthalimide-functionalized chitosan (HN-Chitosan)-based polymeric probe is reported, which takes advantage of specific chemical reaction between HCHO and grafted hydrazino-naphthalimide groups to trigger a "turn-on" fluorescence response. Superior to its small-molecule analogs, HN-Chitosan is based on random coil polymer chains of biopolymeric chitosan, which is thus capable of employing the cooperative binding effect of multiple hydrazino-naphthalimide recognition sites and adjacent hydroxyl groups to "enrich" the low-concentration HCHO pollutant around the polymer chains via weak supramolecular interactions. Therefore, the HCHO-specific chemical reaction with grafted hydrazino-naphthalimide groups is significantly accelerated, resulting in the unprecedented ultrafast equilibrium fluorescence response (less than 1 min) and high sensitivity. Encouraged by its satisfying sensitivity, selectivity, fast response, and wide linear detection range, we successfully expand its application to real-world food and water analysis. In view of the modular design principle of our polymeric probe, the proposed strategy could be generally applicable to construct powerful polymeric probes for ultrafast detection of other important pollutants.

Highly Sensitive and Discriminative Detection of BTEX in the Vapor Phase: A Film-Based Fluorescent Approach

BTEX (benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene) represents a group of volatile organic compounds (VOCs) and constitutes a great threat to human health. However, sensitive, selective, and speedy detection of them on-site and in the vapor phase remains a challenge for years. Herein, we report a film-based fluorescent approach and a conceptual sensor, which shows unprecedented sensitivity, speed, and reversibility to the aromatic hydrocarbons in the vapor phase. In the studies, pentiptycene was employed to produce a nonplanar perylene bisimide (PBI) derivative, P-PBI. The compound was further utilized to fabricate the film. The novelty of the design is the combination of capillary condensation and solvent effect, which is expected to enrich the analytes from vapor phase and shows outputs at the same time. Importantly, the film permits instant response (∼3 s) and real-time identification (<1 min) of benzene and toluene from other aromatic hydrocarbons. The experimental detection limits (DLs) of the six analytes are lower than 9.2, 2.7, 1.9, 0.2, 0.4, and 0.4 ppm, which with the exception of benzene, are significantly lower than the NIOSH recommended long-term exposure limits. More importantly, the film is photochemically stable, and more than 300 repetitive tests showed no observable bleaching. In addition, the sensing is fully reversible. The superior performance of the film device is in support of the assumption that the combination of capillary condensation and solvation effect would constitute an effective way to design high-performance fluorescent films, especially for challenging chemical inert and photoelectronically inactive VOCs.