Synthesis of an efficient Pyrene based AIE active functional material for selective sensing of 2,4,6-trinitrophenol

An investigation of the Excitation Wavelength-Dependent Dynamic Changes in the Mechanism of Detection of Picric Acid using Pyrene-Based Donor-Acceptor Systems

Picric acid (PA) is an important industrial feedstock and hence the release of industrial effluents without proper remediation results in its buildup in soil and water bodies. The adverse effects of PA accumulation in living beings necessitate the development of efficient methods for its detection and quantification. Herein, we describe pyrene-based fluorescent sensors for PA, where pyrene is appended with electron-withdrawing groups, malononitrile, and 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene) malononitrile (DCDHF). These molecules displayed the typical emission of pyrene monomers, as well as a broad red-shifted emission resulting from an intramolecular charge transfer (ICT) in the excited state. Both the emissions displayed a turn-off response to PA with high selectivity and sensitivity and the lowest limit of detection was estimated as 27 nM. To prove the feasibility of on-site detection, test paper strips were prepared, which could detect PA up to 4.58 picograms. Using a combination of experimental and theoretical studies the mechanism of the detection was identified as primary/secondary inner filter effect, oxidative photoinduced electron transfer, or a combination of both depending on the excitation wavelength. Interestingly, the contribution of each of these mechanisms to the total quenching process varied with a change in the excitation wavelength.

Pyrazoline-Based Fluorescent Probe: Synthesis, Characterization, Theoretical Simulation, and Detection of Picric Acid

2-Pyrazoline containing benzothiazole ring 2-[1-(1,3-benzothiazol-2-yl)-5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-3-yl]phenol (BP) have been synthesized for the effective identification of picric acid over other competing nitro compounds using fluorescence technique. The pyrazoline BP showed quenching efficiency as high as 82% comparative to other nitro aromatics. The limit of detection and limit of quantification were found to be 1.1 μM and 3.3 μM. The possible mechanism with the quenched PA detection efficiency was based on fluorescence energy transfer and photoinduced electron transfer. Moreover, the observed results were supported by the optimized structures of the compounds using the DFT/B3LYP/6-311G/LanL2DZ method. Eventually, the pyrazoline derivative BP was further utilized for natural water samples, showing recoveries in the 87.62-101.09% and RSD was less than 3%.

Ligand-protected metal nanoclusters as low-loss, highly polarized emitters for optical waveguides

Photoluminescent molecules and nanomaterials have potential applications as active waveguides, but such a use has often been limited by high optical losses and complex fabrication processes. We explored ligand-protected metal nanoclusters (LPMNCs), which can have strong, stable, and tunable emission, as waveguides. Two alloy LPMNCs, Pt1Ag18 and AuxAg19-x (7 ≤ x ≤ 9), were synthesized and structurally determined. Crystals of both exhibited excellent optical waveguide performance, with optical loss coefficients of 5.26 × 10-3 and 7.77 × 10-3 decibels per micrometer, respectively, lower than those demonstrated by most inorganic, organic, and hybrid materials. The crystal packing and molecular orientation of the Pt1Ag18 compound led to an extremely high polarization ratio of 0.91. Aggregation enhanced the quantum yields of Pt1Ag18 and AuxAg19-x LPMNCs by 115- and 1.5-fold, respectively. This photonic cluster with low loss and high polarization provides a generalizable and versatile platform for active waveguides and polarizable materials.

A Gelation-Induced Enhanced Emission Active Stimuli Responsive and Superhydrophobic Organogelator: "Turn-On" Fluorogenic Detection of Cyanide and Dual-Channel Sensing of Nitroexplosives on Multiple Platforms

A pyrene-based highly emissive low-molecular-weight organogelator, [2-(4-fluorophenyl)-3-(pyren-1-yl)acrylonitrile] (F1), is presented, which divulges thixotropic and thermochromic fluorescence switching via reversible gel-to-sol transition and tremendous superhydrophobicity (mean contact angles: 149-160°), devoid of any gelling and/or hydrophobic units. The rationale for the design strategy reveals that the restricted intramolecular rotation (RIR) in J-type self-assembly promotes F1 for the prolific effects of aggregation- and gelation-induced enhanced emission (AIEE and GIEE). Meanwhile, hindrance in charge transfer via the nucleophilic reaction of cyanide (CN^-) on the C═C unit in F1 facilitates the selective fluorescence "turn-on" response in both solution [9:1 (v/v) DMSO/water] and solid state [paper kits] with significantly lower detection limits (DLs) of 37.23 nM and 13.4 pg/cm², respectively. Subsequently, F1 discloses CN^- modulated colorimetric and fluorescence "turn-off" dual-channel response for aqueous 2,4,6-trinitrophenol (PA) and 2,4-dinitrophenol (DNP) in both solution (DL = 49.98 and 44.1 nM) and solid state (DL = 114.5 and 92.05 fg/cm²). Furthermore, the fluorescent nanoaggregates of F1 in water and its xerogel films permit a rapid dual-channel "on-site" detection of PA and DNP, where the DLs ranged from nanomolar (nM) to sub-femtogram (fg) levels. Mechanistic insights reveal that the ground-state electron transfer from the fluorescent [F1-CN] ensemble to the analytes is responsible for anion driven sensory response, whereas the unusual inner filter effect (IFE) driven photoinduced electron transfer (PET) was responsible for self-assembled F1 response toward desired analytes. Additionally, the nanoaggregates and xerogel films also detect PA and DNP in their vapor phase with reasonable percentage of recovery from the soil and river water samples. Therefore, the elegant multifunctionality from a single luminogenic framework allows F1 to provide a smart pathway for achieving environmentally benign real-world applications on multiple platforms.

Combined Experimental and Theoretical Studies on the Rubbing-Induced Fluorescence Behavior of a Luminophore in the Solid State

It is intricate to break and make chemical bonds in solid states compared to their solution states, so it is imperative to ascertain green proficient approaches by regulating the solid-state structures and their related material properties. Here, the rubbing-induced photoluminescence behavior of a luminophore (RIL) of the benzimidazole family in the solid state has been accomplished. Interestingly, upon gentle rubbing or mere scratching, solid-state fluorescence from the nonemissive pristine RIL was observed due to the aggregation-induced emission (AIE) phenomenon in the solid state, for which the phenolic moiety is present in the molecule and is accountable. The structure-property relationship of RIL and the mechanism responsible for this solid-state fluorescence characteristics have been explained with the help of experimental (using the single-crystal structure, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) images, etc.) and theoretical (by DFT and TDDFT) studies. The crystal arrangements with different stacking interactions and the SEM images after being rubbed revealed that the mechanical force- or pressure-induced slight deformation in the crystal arrangement notably facilitated the strong emission in the solid state. This rubbing-induced solid-state fluorescence in a new luminophore (RIL) through stacking of layers restricting the molecular motion has been developed here for the first time, and it can be explicitly employed in steganography techniques for data security. This present study will open up a new insight into the use of this RIL as a solid-state smart material for data security in coding devices in the future, and this developed approach may be helpful to ameliorate the design of new-generation smart materials by modifying the structure to attain other characteristics.

Copolymers of 4-Trimethylsilyl Diphenyl Acetylene and 1-Trimethylsilyl-1-Propyne: Polymer Synthesis and Luminescent Property Adjustment

Poly(4-trimethylsilyl diphenyl acetylene) (PTMSDPA) has strong fluorescence emission, but its application is limited by the effect of aggregation-caused quenching (ACQ). Copolymerization is a commonly used method to adjust the properties of polymers. Through the copolymerization of 4-trimethylsilyl diphenyl acetylene and 1-trimethylsilyl-1-propyne (TMSP), we successfully realized the conversion of PTMSDPA from ACQ to aggregation-induced emission (AIE) and aggregation-induced emission enhancement (AEE). By controlling the monomer feeding ratio and with the increase of the content of TMSDPA inserted into the copolymer, the emission peak was red-shifted, and a series of copolymers of poly(TMSDPA-co-TMSP) that emit blue-purple to orange-red light was obtained, and the feasibility of the application in explosive detection was verified. With picric acid (PA) as a model explosive, a super-quenching process has been observed, and the quenching constant (K_SV) calculated from the Stern-Volmer equation is 24,000 M^-1, which means that the polymer is potentially used for explosive detection.

Highly Sensitive 'on-off' Pyrene Based AIEgen for Selective Sensing of Copper (II) Ions in Aqueous Media

A Fluorescent chemosensor based on pyrene scaffold, 5-diethylamino-2-(pyren-1-yliminomethyl)-phenol (PDS) is synthesized using condensation method. It displays novel aggregation-induced emission (AIE) phenomena in its aggregated/solid state. The AIE characteristic of PDS is studied in CH₃CN/H₂O mixtures at different volume percentage of water and morphology of the aggregated particles are investigated by DLS and optical fluorescence microscopic study. The probe is aggregated into ordered one-dimensional (1-D) rod like microcrystals and exhibit high efficiency of solid-state emission with green colour. By taking advantage of its interesting AIE feature, the aggregated hydrosol has been utilized as 'off-on' type fluorescence switching chemosensor with superb selectivity and sensitivity towards Cu²⁺ions and the limit of detection (LOD) was calculated as low as 6.3 µM. A high Stern-Volmer quenching constant was estimated to be 2.88 × 10⁵ M^-1. The proposed chemosensor with AIE feature reveals a prospective view for the on-site visual recognition of Cu²⁺ ions in fluorescent paper strips and the synthesized probe is also exploited to find out the concentration of Cu²⁺ions in real water samples.

Fabrication and application of 2,4,6-trinitrophenol sensors based on fluorescent functional materials

2,4,6-Trinitrophenol (TNP) has been widely used for a long time. The adverse effects of TNP on ecological environment and human health have promoted researchers to develop various methods for detecting TNP. Among multifarious technologies utilized for the TNP detection, fluorescence strategy based on different functional materials has become an effective and efficient method attributed to its merits such as preferable sensitivity and selectivity, rapid response speed, simple operation, and lower cost, which is also the focus of review. This review summarizes the development status of fluorescence sensors for TNP in a detailed and systematic way, especially focusing on the research progress since 2015. The sensing properties of fluorescent materials for TNP are the core of this review, including nanomaterials, organic small molecules, emerging supramolecular systems, aggregation induced emission materials and others. Moreover, the development direction and prospect of fluorescence sensing method in the field of TNP detection are introduced and discussed at the end of review.

Hydrazine Detection during Ammonia Electro-oxidation Using an Aggregation-Induced Emission Dye

Ammonia electro-oxidation is an extremely significant reaction with regards to the nitrogen cycle, hydrogen economy, and wastewater remediation. The design of efficient electrocatalysts for use in the ammonia electro-oxidation reaction (AOR) requires comprehensive understanding of the mechanism and intermediates involved. In this study, aggregation-induced emission (AIE), a robust fluorescence sensing platform, is employed for the sensitive and qualitative detection of hydrazine (N₂H₄), one of the important intermediates during the AOR. Here, we successfully identified N₂H₄ as a main intermediate during the AOR on the model Pt/C electrocatalyst using 4-(1,2,2-triphenylvinyl)benzaldehyde (TPE-CHO), an aggregation-induced emission luminogen (AIEgen). We propose the AOR mechanism for Pt with N₂H₄ being formed during the dimerization process (NH₂ coupling) within the framework of the Gerischer and Mauerer mechanism. The unique chemodosimeter approach demonstrated in this study opens a novel pathway for understanding electrochemical reactions in depth.

Pyrrole-quinazoline derivative as an easily accessible turn-off optical chemosensor for Cu2+ and resultant Cu2+ complex as a turn-on sensor for pyrophosphate in almost neat aqueous solution

A simple chemosensor, 6-(1H-pyrrol-2-yl)-5,6-dihydro-benzo[4,5]imidazo[1,2-c]quinazoline (1), was synthesized via simple nucleophilic addition reaction coupled with Schiff base condensation. The probe 1 is aggregation-induced emission-active and could be used as an on-off fluorescence sensor toward Cu²⁺ in H₂O/CH₃CN (99.5%, v/v) solution. Furthermore, the resultant Cu²⁺ complex selectively responded to pyrophosphate (PPi) among various anions based on fluorescent on-off signal. In addition, the probe could be used for detecting Cu²⁺ and PPi in HeLa cells.

Fluorometric determination of the activity of alkaline phosphatase based on a system composed of WS2 quantum dots and MnO2 nanosheets

A fluorometric method is described for the detection of alkaline phosphatase (ALP) activity. It is based on the use of the product of hydrolysis of the drug amifostine (a thiophosphoester) by ALP. It is known that MnO₂ nanosheets quench the blue fluorescence of tungsten disulfide quantum dots (WS₂ QDs) which have excitation/emission wavelengths of 320/448 nm. However, in the presence of ALP and amifostine, the product of hydrolysis [2-(3-aminopropylamino)ethanethiol] triggers the decomposition of the MnO₂ nanosheets. This results in the recovery of fluorescence. Based on this finding, an assay for ALP activity was developed that works in the 0.09-1.6 U L^-1 range, with a 40 mU L^-1 detection limit. The relative standard deviation is 1.87% for five repeated measurements of 0.8 U L^-1 ALP. The method was applied to the analysis of ALP in real samples and gave satifactory results. Graphical abstractSchematic representation of a fluorometric method for determination of the activity of alkaline phosphatase (ALP). The fluorescence of a system composed of WS₂ quantum dots and MnO₂ nanosheets is quenched. Hydrolysis of the cytoprotective adjuvant amifostine (a phosphothioester) by ALP leads to a thiol that causes the decomposition of the MnO2 nanosheets. As a result, the blue fluorescence of the system becomes increasingly restored.

Aggregation-induced emission and the working mechanism of 1-benzoyl and 1-benzyl pyrene derivatives

Over the past decade, research studies on solid-state luminescent materials featuring aggregation-induced emission (AIE) have achieved great success. It has been proved that lots of planar ACQ (aggregation-caused quenching) chromophores can be converted to AIE luminogens (AIEgens) by combining with an AIE-active unit such as tetraphenylethene (TPE). In this work, we present a new method to create AIE luminogens just by introducing benzoyl or benzyl to a planar chromophore, pyrene. The generated 1-benzoyl and 1-benzyl pyrene derivatives exhibit weak emission when molecularly dissolved in good solvents but strong emission from pyrene dimers when aggregated in poor solvent or the solid state. Their crystal structure analysis and theoretical calculations are performed to depict the working mechanism of these new AIEgens. The results show that the structural rigidification of these 1-benzoyl pyrene derivatives is the major cause for their AIE effect. This new AIE system along with a clear working mechanism will contribute to the development of AIE-related functional materials and theories.

Crystal structure of (E)-3-(pyren-1-yl)-1-(pyridin-4-yl)prop-2-en-1-one, C24H15NO

C24H15NO, monoclinic, P21/n (no. 14), a = 10.3161(3) Å, b = 5.53330(10) Å, c = 29.2019(7) Å, β = 97.341(1)°, V = 1653.24(7) Å3, Z = 4, R gt(F) = 0.0423, wR ref(F 2) = 0.1344, T = 294(2) K.