The sensing mechanism of fluoride anion for a novel molecule D2: Desilylation and intramolecular charge transfer

In this work, the sensing mechanism of a new fluoride chemosensor 12‐([tert‐butyldiphenylsilyl]oxy)‐8a,13a‐dihydro‐7H‐benzo[de]benzo[4,5]imidazo[2,1‐a]‐isoquinolin‐7‐one (abbreviated as D2) is investigated using density functional theory (DFT) and time‐dependent DFT (TDDFT) methods. The theoretical electronic spectra (vertical excitation energies and fluorescence peak) reproduced previous experimental results (D. Li et al., Spectrochim. Acta A Mol. Biomol. Spectrosc. 2017 , 185, 173), which confirms the rationality of the theoretical level used in this work. The constructed potential energy curve of the desilylation process suggests that the low barrier could be responsible for the rapid response to fluoride anions. Analyses of the binding energies show that only fluoride anion can be detected by D2 chemosensor in dimethylsulfoxide (DMSO). In view of the excitation process, the strong intramolecular charge transfer (ICT) process of the S₀ → S₁ transition explains the red shift of the absorption peak of the D2 sensor with the addition of fluoride anions. This work not only presents a straightforward sensing mechanism of sensing of the fluoride anion by the D2 chemosensor but should also play an important role in the synthesis and design of fluorescent sensors in future.     

Ion Interactions with a New Ditopic Naphthalimide‐Based Receptor: A Photophysical,NMR and Theoretical (DFT) Study

A new multi‐component chemosensor system comprising a naphthalimide moiety as fluorophore is designed and developed to investigate receptor–analyte binding interactions in the presence of metal and non‐metal ions. A dimethylamino moiety is utilized as receptor for metal ions and a thiourea receptor, having acidic protons, for binding anions. The system is characterized by conventional analytical methods. The absorption and fluorescence spectra of the system consist of a broad band typical for an intramolecular charge transfer (ICT). The effects of various metal‐ion additives on the spectral behavior of the present sensor system are examined in acetonitrile. It is found that among the metal ions studied, alkali/alkaline earth‐metal ions and transition‐metal ions modulate the absorption and fluorescence spectra of the system. As an additional feature, the anion signaling behavior of the system in acetonitrile is studied. A decrease in fluorescence efficiency of the system is observed upon addition of fluoride and acetate anions. Fluorescence quenching is most effective in the case of fluoride ions. This is attributed to the enhancement of the photoinduced electron transfer from the anion receptor to the fluorophore moiety. Hydrogen‐bond interactions between the acidic NH protons of the thiourea moiety and the F^? anions are primarily attributed to the fluoride‐selective signaling behavior. Interestingly, a negative cooperativity for the binding event is observed when the interactions of the system are studied in the presence of both Zn²⁺ and F^? ions. NMR spectroscopy and theoretical calculations are also carried out to better understand the receptor–analyte binding.     

Synthesis,spectroscopic characterization and biological evaluation of a novel chemosensor with different metal ions

A novel chemosensor, namely 3‐(4‐chlorophenyl)‐1‐(pyridin‐2‐yl)prop‐2‐en‐1‐one, CPPEO, and its metal complexes have been synthesized and characterized by using sets of chemical and spectroscopic techniques, such as elemental analysis, mass, Fourier transform‐infrared and UV–Vis spectral analysis. The thermal properties of the metal complexes have been investigated by thermogravimetric techniques. The decomposition mechanism of the titled complexes was suggested. The results showed that the Co²⁺ and Mn²⁺ complexes have an octahedral geometry, while Zn²⁺ and Cd²⁺ complexes have tetrahedral geometry. The kinetic and thermodynamic parameters of the thermal decomposition stages have been evaluated using the Coats–Redfern method. The optical sensing response of the investigated chemosensor to the different metal ions was investigated. It responds well to the tested metal ions as reflected from the significant change in both absorption and emission spectra upon adding different concentrations of the metal salts, confirming the intramolecular charge transfer of the chemosensor upon effective coordination with the used metal ions. This leads to enhancing ICT interaction, causing a significant shift in the presence of strongly complexing metal ions. This was fully reversible, where the solution of dye‐metal ion complex was decomplexed by adding an EDTA solution to revert the original spectrum of the dye. The stability constants, K, for the complexes of the investigated chemosensor with the mentioned metal ions were calculated, indicating that Co²⁺ is the most effectively detected, and the potential of the novel dye was highly efficient switchers for Co²⁺ ions. Additionally, the molecular modeling was carried out for the chemosensor and its metal complexes. Finally, the solid complexes have been tested for their in vitro antimicrobial activities against some bacterial strains (Gram +ve and Gram ?ve bacteria), as well as antifungal strains.     

TD‐DFT study on the sensing mechanism of a fluorescent chemosensor for fluoride: Excited‐state proton transfer

An excited‐state proton transfer (ESPT) process, induced by both intermolecular and intramolecular hydrogen‐bonding interactions, is proposed to account for the fluorescence sensing mechanism of a fluoride chemosensor, phenyl‐1H‐anthra(1,2‐d)imidazole‐6,11‐dione. The time‐dependent density functional theory (TD‐DFT) method has been applied to investigate the different electronic states. The present theoretical study of this chemosensor, as well as its anion and fluoride complex, has been conducted with a view to monitoring its structural and photophysical properties. The proton of the chemosensor can shift to fluoride in the ground state but transfers from the proton donor (NH group) to a proton acceptor (neighboring carbonyl group) in the first singlet excited state. This may explain the observed red shifts in the fluorescence spectra in the relevant fluorescent sensing mechanism. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Theoretical insights into the fluoride anion response mechanism of a fluorescence chemosensor 4‐((tert‐butyldiphenylsilyl)oxy)isophthalaldehyde

It is well known that ions play important roles in our life sciences, and the detection of ions has attracted more and more attention. In this work, we focus on the sensing response mechanism of a novel fluoride chemosensor, 4‐((tert‐butyldiphenylsilyl)oxy)isophthalaldehyde (BIPA). Based on density functional theory and time‐dependent density functional theory methods, we clarify that fluoride anions could trigger the cleavage reaction of the Si‐O bond of BIPA in the ground state. And, the potential energy curve of desilylation process reveals the rapid response to fluoride anions. Comparing the binding energies between fluoride anions and other anions, we confirm that only the fluoride anions could be detected using the BIPA chemosensor in ethanol solvent. Considering the photo‐excitation process, we find the strong intramolecular charge transfer process for the S₀ → S₁ transition could explain the red shift of the absorption spectra of the BIPA system. This work not only clarifies the specific fluoride‐sensing mechanism, but also plays a role in facilitating designing and synthesizing of novel fluorescent sensors in future.     

Highly Selective Colorimetric and Fluorometric Probes for Fluoride Ions Based on Nitrobenzofurazan‐containing Polymers

We report on a novel colorimetric and fluorometric chemosensor for fluoride ions based on 4‐(2‐acryloyloxyethylamino)‐7‐nitro‐2,1,3‐benzoxadiazole (NBDAE)‐labeled polymers. Upon gradual addition of fluoride ions (F^–), the green fluorescence emission of NBDAE moieties can be dramatically quenched, accompanied with the distinct colorimetric transition from green to yellow. NBDAE moieties are capable of selectively recognizing F^– ions via hydrogen‐bonding (H‐bonds) interactions at low F^– concentration and subjected to further deprotonation process at high F^– concentration. NBDAE‐labeled polymers in organic solvents possess high selectivity and fluorescence “turn‐off” characteristics toward the sensing of F^– ions with the detection limit down to ≈0.8 µM .

     

An Anion‐Conjugated Polyelectrolyte Designed for the Selective and Sensitive Detection of Silver(I)

A novel conjugated polyelectrolyte P1, having a meta‐substituted monopyridyl in the backbone, is designed and synthesized for Ag⁺ detection in aqueous solution. As a chemosensor, P1 shows high sensitivity, low detection limit, and excellent selectivity for Ag⁺ over other metal ions. The sensing mechanism is based on the specific interaction between Ag⁺ and the pyridyl group of P1. The aggregated state of the polymer in water can amplify its quenching efficiency.     

Silyl‐protected hydroxystyrenes: Living anionic polymerization at room temperature and selective desilylation

Both 4‐ and 3‐(tert‐butyldimethylsilyl)oxystyrene (MSOST) undergo living anionic polymerization at room temperature with sec‐butyllithium (sBuLi) in cyclohexane or methylcyclohexane upon injection of a small amount of tetrahydrofuran. Desilylation can be conveniently afforded with hydrogen chloride or tetra(alkyl)ammonium fluoride to provide poly(hydroxystyrene) (PHOST) with a narrow molecular weight distribution, which could be further transformed to other polystyrene derivatives. ¹³C NMR spectra of poly(tert‐butyldimethylsilyloxystyrene) (PMSOST) and PHOST prepared under different conditions (tetrahydrofuran vs. cyclohexane, −78 °C vs. 20 °C) have indicated that the room temperature living polymerization in the hydrocarbon‐rich solvent produces polymers with high syndiotacticity. Similarly, 4‐(tert‐butyldiphenylsilyl)oxystyrene (PhSOST), a new monomer, provides living anionic polymerization at room temperature. Desilylation of this polymer can be achieved using tetra(n‐butyl)ammonium or tetraethylammonium fluoride. Inertness of the phenylsilyl ether to HCl allows selective desilylation of the dimethylsilyl ether with HCl in the presence of the phenylsilyl ether group, providing a new route to interesting macromolecules. Application of the selective desilylation technique to the synthesis of a block copolymer of HOST and 4‐tert‐butoxycarbonyloxystyrene (BOCST) is described. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2415–2427, 2000     

Synthesis,Kinetics, and Equilibrium Study of Highly Sensitive Colorimetric Chemosensor for Monitoring of Copper Ions based on Benzo[f]fluorescein Dye Derivatives

The colorimetric chemosensor 2‐((3,5‐dichloro‐2‐hydroxybenzylidene)amino)‐3′,6′‐dihydroxy‐6‐methyl‐4‐(p‐tolyl)spiro[benzo[f]isoindole‐1,9′‐xanthen]‐3(2H)‐one ( BFFSH ) derived from benzo[f]fluorescein dye was synthesized. NMR and IR spectroscopy as well as mass spectrometry were used to confirm the compound. BFFSH shows potential application for detecting metal ions in aqueous solution. It displays a colorimetric selectivity and sensitivity towards the aqueous solution of Cu²⁺ ions with a detection limit in the nano‐molar range (1.69 nM). In addition, the application of BFFSH was extended for the detection of Cu²⁺ ions in real water samples (tap and synthetic water) with a high recovery percentage. Additionally, the association constant (K_a) of BFFSH , which binds with Cu²⁺ ions based on 2:1 stoichiometry was calculated.     

On the Triple Role of Fluoride Ions in Palladium‐Catalyzed Stille Reactions

The mechanism of Stille reactions (cross‐coupling of ArX with Ar′SnnBu₃) performed in the presence of fluoride ions is established. A triple role for fluoride ions is identified from kinetic data on the rate of the reactions of trans‐[ArPdBr(PPh₃)₂] (Ar=Ph, p‐(CN)C₆H₄) with Ar′SnBu₃ (Ar′=2‐thiophenyl) in the presence of fluoride ions. Fluoride ions promote the rate‐determining transmetallation by formation of trans‐[ArPdF(PPh₃)₂], which reacts with Ar′SnBu₃ (Ar′=Ph, 2‐thiophenyl) at room temperature, in contrast to trans‐[ArPdBr(PPh₃)₂], which is unreactive. However, the concentration ratio [F^?]/[Ar′SnBu₃] must not be too high, because of the formation of unreactive anionic stannate [Ar′Sn(F)Bu₃]^?. This rationalises the two kinetically antagonistic roles exerted by the fluoride ions that are observed experimentally, and is found to be in agreement with the kinetic law. In addition, fluoride ions promote reductive elimination from trans‐[ArPdAr′(PPh₃)₂] generated in the transmetallation step.     

2,6-Bis(2-benzimidazolyl)pyridine as a chemosensor for fluoride ions

2,6-Bis(2-benzimidazolyl)pyridine, a neutral tridentate ligand, is employed as a chemosensor for the detection of fluoride ions. The binding of anionic guest species with this ligand is studied using UV-vis spectroscopy, fluorescence spectroscopy, and ¹H NMR techniques. The results indicate that 2,6-bis(2-benzimidazolyl)pyridine can be used as a chemical shift and optical modification based sensor for the detection of fluoride ions.     

A novel and synthetically facile coumarin-thiophene-derived Schiff base for selective fluorescent detection of cyanide anions in aqueous solution: Synthesis,anion interactions,theoretical study and DNA-binding properties

A colorimetric and fluorescent chemosensor (chemosensor 2) for the detection of cyanide anions in aqueous solution has been designed and synthesized in high yield. The sensing mechanism of the chemosensor was verified via UV–vis, fluorimetric, and NMR titrations, and was theoretically explained using DFT and TD-DFT calculations. The chemosensor could optically discriminate the presence of fluoride ions over other anions by a color change from yellow to red with an enhancement of pink fluorescence in DMSO. However, it showed strong green fluorescence when CN^? was added to a mixture of DMSO/water (6:4 v/v). Thus, the chemosensor can be employed in selective detecting of CN^? besides other interference anions (F^?, AcO^? and H₂PO₄^?) in aqueous solution. Moreover, 2 can be used to detect CN^? at a concentration as low as 0.32?μM, which is lower than the WHO guideline (2.7?μM) for cyanide. A low quantity of CN^? (1.08?μM) can be detected and quantified using the prepared chemosensor. Moreover, the UV–vis and fluorescence spectroscopy studies of the interactions between 2 and dublex DNA revealed intercalative binding of calf thymus DNA to the chemosensor.     

Naphthalimide as Highly Selective Fluorescent Sensor for Ag^＋ Ions

The naphthalimide derivative. NA1 was synthesized, which consists of a bis（2-（ethylthio）ethyl）amine group binding cations and naphthalimide unit as chromogenic and fluorogenic signaling subunit. Absorption and emission spectra and the effect of polarity of solvents and pH values were studied. The photo-induced electron transfer （PET） occurred from the donor of bis（2-（ethylthio）ethyl）amine group to the naphthalimide fluorophore. The present study demonstrates that NA1 is a viable candidate as a fluorescent receptor for a new Ag^＋ ion sensor. This silver ion chemosensor can discriminate Ag^＋ ion well among heavy metal ions by an enhancement of the fluorescence intensity in ethanol-water （1 ： 9, V ： V）. And NA1 is also a pH-sensor because the fluorescence of the compound varies with the pH values.     

A tetra-sulfonamide derivative bearing two dansyl groups designed as a new fluoride selective fluorescent chemosensor

A new fluorescent chemosensor based on an acyclic tetra-sulfonamide derivative linked to two dansyl groups has been conveniently synthesized. Its high selective binding ability to fluoride ions over other halide ions was demonstrated by using fluorescence as well as ¹H NMR spectra.     

Synthesis of a Fluorescent Polymer Bearing Covalently Linked Thienylene Moieties and Rhodamine for Efficient Sensing

A novel conjugated polymer (RB‐PPETE) of poly[p‐(phenylene ethynylene)‐alt‐(thienylene ethynylene)] (PPETE) bearing covalently linked thienylene rings and Rhodamine B units has been synthesized and successfully used to detect metal ions. The Rhodamine B exists as a lactone, which is colorless and non‐fluorescent. Hg²⁺ ions can induce the Rhodamine group to form a ring‐opened state. The fluorescence resonance energy transfer (FRET) was demonstrated in the polymer, and in the presence of Hg²⁺ ions the excitation energy along the backbone of the conjugated polymer is transferred to the energy acceptor (Rhodamine B), which leads to a visual color change of the solution from slight yellow to orange. Meanwhile, this new system shows outstanding Hg²⁺‐selective FRET off–on type fluoroionophoric properties among the representative metal ions in tetrahydrofuran.

     

Homopolycyclotrimerization of A4‐type tetrayne: A new approach for the creation of a soluble hyperbranched poly(tetraphenylethene) with multifunctionalities

A tetraphenylethene‐containing A₄‐type tetrayne, named 1,1,2,2‐tetrakis(4‐ethynylphenyl)ethene is synthesized and its TaCl₅‐Ph₄Sn catalyzed homopolycyclotrimerization affords hyperbranched poly(tetraphenylethene) with high molecular weight (M_w = 280,000) in high yield (97%). The polymer shows good solubility and high thermal stability. It is aggregation‐enhanced emission (AEE)‐active and functions as a fluorescent chemosensor for explosive detection with a superamplification effect and large quenching constants up to 758,000 M^?1. The polymer shows high and tunable refractive indices (RI = 1.9288?1.6746) in a wide wavelength region. Porous fluorescent polymer thin film is prepared by breath figure (BF) methods and real‐time monitoring of the elusive BF formation process is realized. Photolithography of the thin films readily generates well‐resolved fluorescent photopattern without and with porous secondary structure. The polymer is metallified and pyrolysed to give magnetic ceramics with high magnetic susceptibilities (M_s = 83 emu/g) and near‐zero coercivity (H_c = 0.08 kOe). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4752–4764     

Nanohybrid Chemosensor for the Simultaneous Detection of Fluoride and Iodide in Aqueous System and Its Utility in Real Samples

A nanohybrid chemosensor for specific, selective and simultaneous recognition of iodide and fluoride was prepared through decoration of silver nanoparticles onto Schiff‐Base based organic nanoparticles. The developed chemosensor showed specific recognition ability for this analytes at low concentrations with detection limits at 690 nM for fluoride and 11 nM for iodide in two different regions of DPV profiles. Theoretical calculations based in Density Functional Theory were performed, which supports experimental results by demonstrating the binding selectivity of nanohybrids with I^? and F^?. The proposed sensor was also used for real sample analysis and results were verified using some standard literature method.     

A New,Highly Potent 1,8‐Naphthalimide‐based Fluorescence “Turn off” Chemosensor Capable of Cu2+ Detection in China's Yellow River Water Samples

A new 1,8‐naphthalimide‐based fluorescence “turn off” chemosensor, N‐phenyl‐4‐(3,3′‐((2‐aminoethyl)azanediyl)dipropanoic acid)‐1,8‐naphthalimide ( MAST ), for the detection of Cu²⁺ was synthesized. Upon treatment with Cu²⁺, in coexistence with various competitive metal ions in HEPES‐buffered dimethylsulfoxide (DMSO) solution (v/v, 1:1; pH 7.4), MAST displayed a high selectivity toward Cu²⁺ with a fluorescence quenching of 83.67%. Additionally, a good linear response of MAST for the detection of Cu²⁺ was obtained in the concentration range of 10 × 10⁻⁶ to 50 × 10⁻⁶ M. A 1:1 stoichiometric interaction of MAST with Cu²⁺ was observed, and the association constant and detection limit were calculated to be 1.37 × 10⁶ and 0.69 × 10⁻⁸ M, respectively. The sensing mechanism of the chemosensor toward Cu²⁺ was proposed due to the effect of the paramagnetic nature of Cu²⁺ and reverse‐photo‐induced electron transfer (PET) process. Ultimately, the proposed chemosensor was applied to quantify Cu²⁺ in real‐world water samples, with excellent recovery rates of 98.00–109.80% observed.     

Selective and sensitive optical chemosensor for detection of Ag(I) ions based on 2(4-hydroxy pent-3-en-2-ylideneamine) phenol in aqueous samples

A selective and sensitive chemosensor, based on the 2(4-hydroxy pent-3-en-2-ylideneamine) phenol (HPYAP) as chromophore, has been developed for colorimetric and visual detection of Ag(I) ions. HPYAP shows a considerable chromogenic behavior toward Ag(I) ions by changing the color of the solution from pale-yellow to very chromatic-yellow, which can be easily detected with the naked-eye. The chemosensor exhibited selective absorbance enhancement to Ag(I) ions in water samples over other metal ions at 438 nm, with a linear range of 0.4–500 μM (r² = 0.999) and a limit of detection 0.07 μM of Ag(I) ions with UV–vis spectrophotometer detection. The relative standard deviation (RSD) for 100 μM Ag(I) ions was 2.05% (n = 7). The proposed method was applied for the determination Ag(I) ions in water and waste water samples.     

Fluoride‐ion‐conducting Polymers: Ionic Conductivity and Fluoride Ion Diffusion Coefficient in Quaternized Polysulfones

We describe the three‐step synthesis of a new polymeric fluoride ion conductor based on the fully aromatic polymer polysulfone (PSU). In the first step, PSU is chloromethylated (CM‐PSU) using reagents (i.e., stannic chloride, paraformaldehyde, and trimethylchlorosilane) that are less toxic than those used in the standard procedure. In the second step, CM‐PSU reacts with a tertiary amine (trimethylamine or 1,4‐diazabicyclo[2.2.2]octane) to form quaternary ammonium groups fixed on the PSU backbone and mobile chloride counter‐anions. The chloride ions can, in a third step, be exchanged with fluoride ions by immersion of the ionomer in NaF solution. The fluoride ion conductivity reaches 3–5 mS cm^?1 at 25 °C and 5–10 mS cm^?1 at 40 °C. We determined the F^? diffusion coefficient in these ionomers by pulsed gradient spin‐echo (PGSE) high‐resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) spectroscopy and by impedance spectroscopy using the Nernst–Einstein relation. The diffusion coefficients determined by the two methods are in good agreement, ranging from 2 to 4×10^?10 m² s^?1. The porosity and tortuosity of the ionomer membranes can be estimated.