Water-soluble ionic liquid as a fluorescent probe towards distinct binding and detection of 2,4,6-trinitrotoluene and 2,4,6-trinitrophenol in aqueous medium

Fluorescence Quenching and Electron Transfer Dynamics of a Thiophene-Substituted 1,3,4-Oxadiazole Derivative with Nitroaromatic Compounds

This study investigates the fluorescence quenching behavior of a newly synthesized thiophene-substituted 1,3,4-oxadiazole derivative, 2-(4-(4-vinyl phenyl)phenyl)-5-(5-(4-vinyl phenyl)thiophene-2-yl)-1,3,4-oxadiazole (TSO), in the presence of various nitroaromatic compounds (NACs), including 2-nitrotoluene, 4-nitrotoluene, nitrobenzene, and picric acid (2,4,6-trinitrophenol). The interactions were examined in an ethanol medium at room temperature using steady-state and time-resolved fluorescence spectroscopy. Steady-state fluorescence analysis revealed a non-linear Stern-Volmer (SV) plot exhibiting positive deviation, while time-resolved measurements displayed a linear relationship. To interpret these findings, ground-state complex formation and the sphere-of-action static quenching models were applied. The study determined key quenching parameters, including the Stern-Volmer constant, quenching rate constant, static quenching constant, and sphere-of-action radius. Notably, fluorescence quenching efficiency increased with the number of NO2 groups in the NACs.Electrochemical analysis, complemented by Density Functional Theory (DFT) calculations, confirmed that electron transfer was the primary quenching mechanism. Furthermore, binding site analysis demonstrated a 1:1 binding stoichiometry between TSO and NACs, with picric acid exhibiting the highest binding affinity. Given the growing interest in fluorescence-based sensing approaches, these findings contribute valuable insights into the development of advanced sensors for detecting nitroaromatic pollutants and explosive residues.

Mitigating ACQ and enhancing solubility: A dual strategy for real-time aquatic product freshness detection

Commercial fluorescent dyes for freshness detection are hindered by aggregation-caused quenching (ACQ) and poor solubility, compromising sensitivity to ammonia. Herein, we employ a dual strategy for designing fluorescein-based ionic liquid micelles to address these challenges: an electronic isolation approach to sensitize the commercial dye and a micelle preparation technique to enhance hydrophilicity. The electronic isolation strategy facilitated the design of an ionic liquid fluorescent probe, [P66614]2[Fluo], derived from fluorescein, which effectively emitted fluorescence in highly aggregated states, thus mitigating ACQ. Additionally, the micelle preparation strategy improved the hydrophilicity of [P66614]2[Fluo], enhancing its water solubility to 3.385 g/L and increasing the detection limit sensitivity for ammonia by more than threefold, achieving 3.8 ppb. This dual strategy was pivotal in overcoming the inherent limitations of conventional dyes, resulting in enhanced fluorescence and improved solubility for efficient ammonia detection. We then developed a dual-signal composite micelle probe combining [P66614]2[Fluo] and Nile Red, which exhibited a wide detection range (0-35.0 ppm), ultralow detection limit (10 ppb), and high selectivity for biogenic amines. The practicality of this system was validated through the use of gel bead devices integrated with smartphone-based analysis for quantitative assessment of shrimp freshness, with results corroborated by traditional total volatile basic nitrogen (TVB-N) methods. This cost-effective, rapid-response, and nondestructive portable device presents a promising platform for real-time freshness detection of aquatic products.

CoFe-MOF nanoarray as flexible microelectrode for electrochemical detection of catechol in water samples

A simple, selective, and straightforward enzyme-free electrochemical sensor has been designed and developed using cobalt hexacyanoferrate metal-organic framework (CoFe-MOF) nanoarray. The prepared CoFe-MOF nanoarray has been successfully grown over a carbon cloth (CC) to form CoFe-MOF/CC as a flexible microelectrode for the detection of catechol. The surface of the activated CC was covered uniformly with CoFe-MOF in the form of nanoarray and exhibited double-shelled cubic morphology. The CoFe-MOF/CC nanoarray microelectrode showed a pair of well-defined redox peaks corresponding to the [Fe(CN)6]4-/3- redox signal. Interestingly, the fabricated nanoarray microelectrode has displayed superior peak current at lower onset potential with high electrochemical response compared to unmodified potassium hexacyanoferrate (K3 [Fe(CN)6]) over CC microelectrode and bare activated CC. Further, the developed CoFe-MOF/CC nanoarray microelectrode for the oxidation of catechol was examined with consecutive injections of catechol. A fast and noticeable improvement in oxidation peak current was observed, thus representing the excellent electrocatalytic oxidation of catechol at the modified nanoarray microelectrode. Besides, CoFe-MOF/CC microelectrode exhibits an excellent linear response over a concentration range from 0.005 to 2.8 mM with low detection limit (LOD) and high sensitivity of 0.002 mM (S/N = 3) and 205.99 μA/mM, respectively. Moreover, the prepared nonenzymatic sensor showed outstanding stability, acceptable reproducibility, and repeatability, along with good interference ability. Catechol in spiked water samples was successfully quantified.

Aggregation-induced emission enhancement (AIEE) active bispyrene-based fluorescent probe: "turn-off" fluorescence for the detection of nitroaromatics

The detection of nitroaromatic explosives in real samples is essential for environmental monitoring because of their strongly powerful nature and wide applications in industries. Aggregation-induced emission enhancement (AIEE) active fluorescent probe has been widely employed to detect nitroaromatic explosives. Hereby, a simple V-shaped bispyrene-based fluorescent probe (called py-o) with AIEE properties was designed and synthesized, which was fully charactered by 1D NMR, ESI, FTIR, and 2D NOESY spectra. The py-o displayed bright blue-green fluorescence excimer emission at 480 nm in DMF/H2O (v/v 1:1). It is observed that the fluorescence excimer emission of py-o at 480 nm was quenched by PA in solution with a quenching constant of 5.45 × 104 M-1, and the limit of detection was approximately 0.139 μM. The details of the sensing mechanism were explained using 1H NMR titrations, Job's plot and Bensi-Hildebrand methods, which revealed a 1:1 binding ratio via the π-π interactions between PA and py-o. Meanwhile, it exhibited outstanding anti-interference ability in the detection of PA when interfering analytes were added under the same conditions. Furthermore, low-cost thin-layer chromatography (TLC) plates coated with py-o were developed as fluorescent tools for naked-eye detection of PA in the solid state. Therefore, this work provides a new method for constructing an AIEE fluorescent probe for the detection of nitroaromatic explosives to utilize in environmental monitoring.

Extensive optical and DFT studies on novel AIE active fluorescent sensor for Colorimetric and fluorometric detection of nitrobenzene in Solid, solution and vapor phase

An electron rich isophthalamide based sensor IPA has been synthesized through a simple two-step reaction, containing noteworthy aggregation induced emission (AIE) properties. Considering the significant emission with λmax at 438 nm, sensor IPA has been employed for the sensing of nitrobenzene (NB) in solid, solution and vapor state with high sensitivity and selectivity. Sensor IPA showed noteworthy colorimetric and fluorometric quenching in fluorescence emission when exposed to NB. Small size of NB and involvement of photoinduced electron transfer (PET) lead to detection of NB down to 60 nM. IPA-NB interaction was studied through UV-Vis. spectroscopic studies along with fluorescence spectroscopy. Moreover, 1H and 13C NMR titration experiments provided additional support for determination of interaction type. Furthermore, by using density functional theory (DFT) calculations, thermodynamic stability was studied. Additionally, non-covalent interactions (NCI), frontier molecular orbitals (FMO), density of states (DOS), were investigated for providing further evidence of nitrobenzene sensing and its interaction with sensor. Natural bond orbital (NBO) analysis was carried out for charge transfer studies. Quantum theory of atom in molecule (QTAIM) and SAPT0 studies provided information about interaction points and binding energy. Additionally, IPA was investigated for NB sensing in real water samples, and its effective participation in solid state on-site detection as well as in solution phase was brought to light along with logic gate construction.

N-octylpyridine hydrogen sulphate ionic liquid for multifunctional fluorescent response in different solvents

Ionic liquids (ILs) have attracted considerable interest in the last two decades owing to their unique fluorescent properties. Herein, N-octylpyridine hydrogen sulphate ([OP]HSO4) was synthesised and characterised using 1H NMR and infrared spectroscopies. In addition, the fluorescence spectra of [OP]HSO4 in water, methanol, ethanol and acetonitrile were studied. In a single solvent, as the concentration of the solvent (methanol, ethanol or acetonitrile) increases, the fluorescence intensity of the IL first increases and then decreases. A similar trend was observed in their mixed solvents with water. Moreover, the fluorescence intensity of [OP]HSO4 decreases with increasing temperature. A fluorescence intensity reduction of only 4.46% for [OP]HSO4 after continuous scanning for 40 cycles under the maximum excitation state was analysed. The lack of photobleaching observed in [OP]HSO4 indicates its good photobleaching resistance.

Electropolymerization of Preferred-Oriented Conjugated Microporous Polymer Films for Enhanced Fluorescent Sensing

High-quality conjugated microporous polymer (CMP) films with orientation and controlled structure are extremely desired for applications. Here, we report the effective construction of CMP 3D composite films (pZn/PTPCz) with a controlled porosity structure and preferred orientation using the template-assisted electropolymerization (EP) approach for the first time. The structure of pZn/PTPCz composite thin films and nitrophenol sensing performance were thoroughly studied. When compared to the control CMP film made on flat indium tin oxide (ITO) substrates, the as-prepared pZn/PTPCz composite films showed significantly enhanced fluorescent intensity and much better sensing performance for the model explosive. This was attributed to the metal-enhanced fluorescence (MEF) of porous nanostructured zinc (pZn) and the additional macroporosity of the pZn/PTPCz composite films. This work provides a feasible approach for creating oriented 3D CMP-based thin films for advanced applications.

Advances in ionic liquids as fluorescent sensors

Ionic liquids (ILs) are a class of liquid salts with characteristics such as a low melting point, an ionic nature, non-volatility, and tunable properties. Because of their adaptability, they have a significant influence in the field of fluorescence. This paper reviews the primary literature on the use of ILs in fluorescence sensing technologies. The kind of target material is utilized to classify the fluorescence sensors made with the use of ILs. They include using ILs as probes for metals, nitro explosives, small organic compounds, anions, and gases. The efficacy of an IL-based fluorescence sensor depends on the precise design to guarantee specificity, sensitivity, and a consistent reaction to the desired analyte. The precise method can differ depending on the chemical properties of the IL, the choice of fluorophore, and the interactions with the analyte. Overall, the viability of the aforementioned materials for chemical analysis is evaluated, and prospective possibilities for further development are identified.

AIE/AEE tripodal PEGyl-melphalan supramolecules and detection of trinitrophenol in water

Herein, the design of a novel aggregation-induced emission (AIE) supramolecular fluorescence sensor (TA-PEGn) based on a tridentate melphalan derivative and three different molecular weight PEGs is presented. The three TA-PEGn sensors could self-assemble into a supramolecular system in water and show sensitive and selective responses toward trinitrophenol.

An extensive experimental and DFT studies on highly selective detection of nitrobenzene through deferasirox based new fluorescent sensor

A deferasirox based substituted triazole amine sensor TAD has been synthesized for the highly selective detection of nitrobenzene in real samples. Sensor TAD exhibited selective quenching response against nitrobenzene among the other nitroaromatic compounds (NACs). Photoinduced electron transfer (PET) process was devised as plausible sensing mechanisms which was supported via UV-visible and fluorescence spectroscopy, 1H NMR titration experiment, density functional theory (DFT) analysis and Job's plot. Non-covalent interaction (NCI) analysis and Bader's quantum theory of atoms in molecules (QTAIM) analysis were performed to investigate the presence of non-covalent interactions and symmetry perturbation theory (SAPT0) was performed for energy decomposition and quantitative analysis of interaction energies between sensor TAD and NB. Furthermore, sensor TAD was practically applied for the identification of NB in real samples.

Selective detection of ionic liquid fluorescence probes for visual colorimetry of different metal ions

At present, the fast distinction of different metal ions in pure water media is not only a great challenge, but also drives the protection of water quality in environmental water bodies. In this paper, a novel ionic liquid fluorescent probe Glycolic Acid-L-Arginine (GA-L-Arg) was rationally created and designed through an in-depth study of ionic liquids. It is also used as an innovative multi-ion fluorescent probe for colorimetric detection and separate identification of Fe3+ and Co2+ in aqueous solutions of various metal ions. GA-L-Arg has excellent water solubility due to the strong hydrophilicity of Glycolic Acid and L-Arginine. The probe showed high sensitivity, extremely significant selectivity, and great pH stability for Fe3+ and Co2+ in pure water. The GA-L-Arg structure and the mechanism of Fe3+ and Co2+ detection were analyzed by infrared spectroscopic characterization and quantum chemical calculations. More importantly, the distinct colorimetric partitioning of Fe3+ and Co2+ was performed by the unique extraction of Fe3+ in the presence of the fluorescent probe and buffer solution.

A facile and sensitive hexahomotrioxacalix[3]arene-based fluorescent sensor for the detection of trace amounts of 2,4,6-trinitrophenol

Nitroaromatic compounds are common explosives and toxic pollutants, the selective and sensitive detection of which is of great importance. Herein, a facile and sensitive fluorescent sensor L was constructed for the sensing of TNP based on the hexahomotrioxacalix[3]arene skeleton. The fluorescence emission of L was drastically quenched in the presence of 2,4,6-trinitrophenol (TNP), while other tested NACs, metal ions, and anions induced negligible changes. Under the optimized conditions, the spectroscopic studies revealed that L exhibited extremely sensitive and selective TNP recognition, with a detection limit of 9.17 × 10-7 M and a quenching constant of 2.44 × 104 M-1. The sensitivity of sensor L for TNP was attributed to the formation of a ground-state charge-transfer complex and an inner filter effect, which also contributed to the special selectivity of the sensor among the various nitroaromatic analogues. Compared with previous reports, L can serve as a highly efficient sensor for the sensing of TNP and can be employed over a wide pH range of 2 to 12. Sensor L was effectively used to quantify TNP in real water and soil samples. Additionally, fluorescent test strips were also developed for visual and rapid detection of TNP in both the solution and vapour phases.

AIEE active J-aggregates of naphthalimide based fluorescent probe for detection of Nitrobenzene: Combined experimental and theoretical approaches for Non-covalent interaction analysis

A new naphthalimide-based fluorescent probe NS with exceptional J-aggregates based aggregation-induced emission enhancement (AIEE) properties was rationally synthesized through a single-step imidation reaction. Probe NS exhibited excellent AIEE properties in aqueous media through the formation of J-aggregates with remarkable red-shift. The AIEE active probe NS was used for selective and sensitive detection of nitrobenzene (NB) based on fluorescence quenching response. Formation of J-aggregates was assessed through fluorescence titration. These J-aggregates contributed significantly to produce favorable interaction between probe NS and NB. The highly selective fluorescence detection of NB was accredited to the adjustable smaller size of NB that can easily penetrate into interstitial spaces of probe molecules. Ability of sensor to detect NB in solid state was also accomplished through solid state fluorescence spectroscopy. Nature of interaction and sensitivity of probe NS for NB has also been investigated through ¹H NMR titration and density functional theory (DFT) including non-covalent interaction (NCI), quantum theory of atom in molecule (QTAIM), electron density differences (EDD), frontier molecular orbitals (FMO) and density of states (DOS) analysis. Advantageously, probe exhibited colorimetric and vapor phase detection of NB. Moreover, probe was quite sensitive for the trace detection of NB in real samples.

Further Develop 1,3,4-Thiadiazole Based Probe to Effectively Detect 2,4,6-Trinitrophenol with the Help of DFT Calculations

Four fluorimetric probes had been developed to rapidly detect 2,4,6-trinitrophenol (TNP). They were designed and synthesized on the basis of 1,3,4-thiadiazole framework combining calculation with experiment. Among them, SK-1 displayed strong blue emission with fluorescence quantum yield as high as 63.6% in solution. Further evaluation demonstrated that SK-1 displays good selectivity and high sensitivity for rapid and visual detection of TNP. It brought significant changes in both colour and fluorescence emission spectrum. The detection limit was as low as 38 nM. Quenching mechanism was confirmed as photo-induced electron transfer (PET) by nuclear magnetic titration and DFT calculations. What's more, application in real water samples and solid phase paper tests illustrated the practical significance of detection of TNP in both vapor and solution.