Synthesis and evaluation of fluorimetric and colorimetric chemosensors for anions based on (oligo)thienyl-thiosemicarbazones

A family of heterocyclic thiosemicarbazone dyes (3a–d) containing thienyl groups has been synthesized, characterized, and their chromo-fluorogenic response in acetonitrile in the presence of selected anions was studied. Acetonitrile solutions of 3a–d show absorption bands in the 338–425 nm range, which are modulated by the groups attached to the thiosemicarbazone moiety. The fluoride, chloride, bromide, iodide, dihydrogen phosphate, hydrogen sulfate, nitrate, acetate, and cyanide anions were used in the recognition studies. Only sensing features were observed for fluoride, cyanide, acetate, and dihydrogen phosphate anions. Two different chromogenic responses were found, (i) a small shift of the absorption band due to coordination of the anions with the thiourea protons and (ii) the appearance of a new red-shifted band due to deprotonation of the receptor. For the latter process changes in the color solutions from pale-yellow to orange-red were observed. Fluorescence studies showed a different emission behavior according to the number of thienyl rings in the π-conjugated bridges. Stability constants for the two processes (complex formation+deprotonation) for receptors 3a–d in the presence of fluoride and acetate anions were determined from spectrophotometric titrations using the HypSpec program. The interaction of 3d with fluoride was studied through ¹H NMR titrations. Semiempirical calculations to evaluate the hydrogen-donating ability of the receptors were also performed.     

An exclusive fluoride receptor: fluoride-induced proton transfer to a quinoline-based thiourea

A new quinoline-based tripodal thiourea has been synthesized, which exclusively binds fluoride anion in DMSO, showing no affinity for other anions including chloride, bromide, iodide, perchlorate, nitrate, and hydrogen sulfate. As investigated by ¹H NMR, the receptor forms both 1:1 and 1:2 complexes yielding binding constants of 2.32(3) (in log β₁) and 4.39(4) (in log β₂), respectively. The quinoline groups are protonated by fluoride-induced proton transfer from the solution to the host molecule. The 1:2 binding is due to the interactions of one fluoride with NH binding sites of urea sites and another fluoride with secondary ⁺NH binding sites within the tripodal pocket. The formation of both 1:1 and 1:2 complexes has been confirmed by theoretical calculations based on density functional theory (DFT).     

Study on Synthesis and Binding Ability of a New Anion Receptor Containing NH Binding Sites

A new colorimetric recognition receptor 1 based on the dual capability containing NH binding sites of selectively sensing anionic guest species has been synthesized. Compared with other halide anions, its UV/Vis absorption spectrum in dimethyl sulfoxide showed the response toward the presence of fluoride anion with high selectivity, and also displayed dramatic color changes from colorless to yellow in the presence of TBAF （5 × 10^-5 mol/L）. The similar UV/Vis absorption spectrum change also occurred when 1 was treated with AcO^- while a little change with H2PO^-4 and OH^-. Receptor 1 has almost not affinity abilities to Cl^-, Br^- and I^-. The binding ability of receptor 1 to fluoride with high selectivity over other halides contributes to the anion size and the ability of forming hydrogen bonding. While the different ability of binding with geometrically triangular （AcO^-）, tetrahedral （H2PO^-4 ） and linear （OH^-） anions maybe result from their geometry configuration.     

A novel, simple, colorimetric receptor based on 2′,4′-dinitrophenylhydrazone for acetate ion in organic medium

A novel 1,3-di(2′,4′-dinitrophenylhydrazone)-5-nitrobenzene receptor has been synthesized by simple steps with good yields. The anion recognition properties were studied by ultraviolet-visible (UV-Vis) spectroscopy. The results showed that the receptor had a higher affinity to F^?, CH₃COO^? and H₂PO ₄ ^? , but no evident binding with Cl^?, Br^?, and I^?. Upon addition of the three former anions to the receptors in dimethyl sulphoxide (DMSO) at 298.2 ± 0.1 K, the solution exhibited an obvious color change from yellow to mauve that could be observed by the naked eye, thus the receptor could act as a fluoride ion sensor even in the presence of other halide ions. The UV-Vis data indicates that a 1:1 stoichiometry complex formed through hydrogen-bonding interactions between receptor and anions. The hydrogen bond between phenylhydrazone –NH and acetate or fluoride anion was determined on the basis of ¹H nuclear magnetic resonance (NMR) experiments.     

Anion sensing properties of new colorimetric chemosensors based on macrocyclic ligands bearing three nitrophenylurea groups

Two new colorimetric ligands (1-2) based on macrocyclic structures linked to three nitrophenylurea groups were synthesized in good yields, and their responses toward anions were studied. Anions with different shape, such as of fluoride, chloride, bromide, iodide, hydroxide, nitrate, perclhorate, cyanide, or dihydrogen phosphate in DMSO solution were added and only fluoride, hydroxide, cyanide, and dihydrogen phosphate enhances π delocalization and shifts the π-π^∗ transition in both ligands, leading to the generation of a pleasant orange color.The result is a balance between the acidity of the nitrophenylurea-NH donors modulated by the basic character of the anions. Stability constants for both receptors and the anions fluoride, hydroxide, cyanide, and dihydrogen phosphate were determined spectrophotometrically using the program HYSPEC. ¹H NMR titrations experiments with fluoride were carried out.     

From a Tb<Superscript>3+</Superscript> chelated compound to a hybrid material: selective emission responses to anions

A novel terbium 2-hydroxymethyl-benzoimidazole-6-carboxylic acid complex has been designed and unique emission changes to fluoride anions in comparison with HSO₄⁻, AcO⁻, Cl⁻, Br⁻, and I⁻ were observed. Then, the complex was encapsulated into an inorganic matrix. The novel hybrid material, with strong green emission was successfully synthesized as an anions receptor in water. More importantly, this hybrid material not only gave luminescence response to F⁻, but also to HSO₄⁻. Spectroscopic studies demonstrated that the recognition process for fluoride ions can be mainly ascribed to its hydrogen bonding interactions with hydrogen bond donor units (NH and OH). In case of hydrogen sulfate, the sensing effects can be probably attributed to its acidity instead of hydrogen bonding interactions.     

Naked-eye detection of cyanide ions in aqueous media based on an azo-azomethine chemosensor

The optical and colorimetric properties of a new chemosensor 4-((2,4-dichlorophenyl)diazenyl)-2-(3-hydroxypropylimino)methyl)phenol (L) for cyanide ions were investigated by the naked-eye detection and UV–vis spectroscopy. This receptor reveals visual changes toward CN⁻ anions in aqueous media. No significant color changes were observed upon the addition of any other anions. The cyanide recognition properties of the receptor through proton-transfer were monitored by UV–vis titration and ¹H NMR spectroscopy. The binding constant (K_a) and stoichiometry of the formed host–guest complex were calculated by the Benesi–Hildebrand (B–H) plot and Job's plot method, respectively. The detection limit of the probe towards CN⁻ was 1.03 × 10⁻⁶ mol L⁻¹, which is lower than the maximum value of cyanide (1.9 × 10⁻⁶ mol L⁻¹) permitted by the World Health Organization in drinking water. Thus, this chemosensor was sensitive enough to detect cyanide in aqueous solutions. ¹H NMR experiments were conducted to investigate the nature of interaction between the receptor and CN⁻ anions. Notably, the designed sensor can be applied for the rapid detection of cyanide anions in the basic pH range and also under physiological conditions, for practical purposes for a long duration. The sensing behavior of the receptor was further emphasized by computational studies. Quantum-chemical calculations and molecular studies via Density Functional Theory (DFT) were carried out to supplement the experimental results.     

Solid-state emissive triarylborane-based BODIPY dyes: photophysical properties and fluorescent sensing for fluoride and cyanide ions

We disclose two novel BODIPY dyes, which contain the bulky substituent, [(4-dimesitylboryl)phenyl]ethynyl at 2- and 2,6-positions. The steric bulkiness of the boryl group is effective to suppress the intermolecular interaction in the solid state and thus these two compounds display intense fluorescence not only in solution but also in the solid state. In addition, the BODIPY dyes display sensitive fluorescence responses to fluoride and cyanide anions through the complexation with the boron center of the boryl group and the subsequent decomposition of the BODIPY core, illustrating their potential uses for the fluorescence sensing of fluoride and cyanide ions.     

Fluoride anion sensing using colorimetric reagents containing binaphthyl moiety and urea binding site

Four 1,1′-binaphthalene based bis-urea derivatives bearing aryl groups at end-on nitrogen atoms IIIa–d were synthesized as potential sensor molecules. These receptors show characteristic UV-VIS spectral changes on complexation with anions and they exhibit selective recognition of F⁻ over other halide anions. Interaction of a fluoride anion with urea NH groups was confirmed by ¹H NMR data. The presence of an electron-withdrawing nitro group in N′-aryls (receptors IIIa and IIIb) appeared to be necessary for naked-eye colorimetric detection. These receptors show dramatic color change from light-yellow to orange (IIIa) or to orange-red (IIIb) in the presence of guest fluoride anions already at concentrations of 10⁻⁵ mol dm⁻³ of the receptor and host.     

Cu and CN-selective fluorogenic sensors based on pyrene-appended thiacalix[4]arenes

Two new fluorescent sensors 1 and 2 based on thiacalix[4]arenes bearing pyrene moieties have been synthesized in cone conformation. The binding abilities of these sensors towards different cations such as lithium, sodium, potassium, nickel, cadmium, copper, zinc, lead, silver, mercury and anions like fluoride, chloride, bromide, iodide, cyanide, acetate, hydrogen sulfate and nitrate have been examined by UV-vis and fluorescence spectroscopies. These receptors show pronounced selectivity for copper and cyanide ions. In CH₂Cl₂/CH₃CN (1:1), the presence of Cu(II) ion induces the formation of 1:1 (H/G) complex with receptor 1 and 1:2 (H/G) complex with receptor 2. The cyanide ions form a 1:1 (H/G) complex with both receptors.     

A novel anthracene-based receptor: Highly sensitive fluorescent and colorimetric receptor for fluoride

A new highly sensitive colorimetric receptor 1 for fluoride based on anthracene-9,10-dicarbaldehyde bis-p-nitrophenylhydrazone was designed, synthesized and characterized. Experiments showed that the receptor 1 can selectively recognize the fluoride in DMSO and even in 95/5 DMSO/H₂O (v/v) mixtures. The ability of recognition and the bond between receptor 1 and anions were determined using visual inspection, UV-vis and fluorescence analyses. In addition, ¹H NMR experiments were carried out to explore the nature of interaction between receptor 1 and fluoride. Finally, analytical application and detection of fluoride in toothpaste have been studied.     

Anion binding behavior of heterocycle-strapped calix[4]pyrroles

A comparative study of the halide and benzoate anion binding properties of a series of phenyl, pyrrole, and furan-strapped calix[4]pyrroles has been carried out. These receptors, which have previously been shown to bind the chloride anion (Yoon et al., Angew. Chem., Int. Ed. 47(27):5038–5042, 2008), were found to bind bromide and benzoate anion (studied as the corresponding tetrabutylammonium salts) with near equal affinity in acetonitrile, albeit less well than chloride, as determined from ITC measurements or NMR spectroscopic titrations. This stands in marked contrast to the parent octamethylcalix[4]pyrrole, where the carboxylate anion affinities are substantially higher than those for bromide anion under identical conditions. This finding is rationalized in terms of tighter binding cavity present in the strapped systems. For all three anions for which quantitative data could be obtained (i.e., Cl^?, Br^?, PhCO₂ ^?), the pyrrole-strapped system displayed the highest affinity, although the relative enhancement was found to depend on the anion in question. In the specific case of fluoride anion binding to the pyrrole-strapped receptor, two modes of interaction are inferred, with the first consisting of binding to the calix[4]pyrrole via NH-anion hydrogen bonds, followed by a process that involves deprotonation of the strapped pyrrolic NH proton. A single crystal X-ray diffraction analysis provides support for the first of these modes and further reveals the presence of a methanol molecule bound to the fluoride anion.     

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.     

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.     

Triphenylamine-based simple chemosensor for selective fluorometric detection of fluoride, acetate and dihydrogenphosphate ions in different solvents

Triphenylamine-based new chemosensors 1 and 2 have been designed and synthesized for fluorometric detection of anions. The urea-amide conjugates in 1 and 2 are involved in binding of anions via hydrogen bonding. UV?Cvis and fluorescence titration experiments revealed that the sensor 1 has the selectivity for acetate (AcO^?), dihydrogenphosphate (H₂PO₄ ^?) and fluoride (F^?) over the other anions examined in the present study, in CHCl₃. In comparison, receptor 2 is non responsive for the same anions under similar conditions. In more polar solvent CH₃CN containing 0.1% DMSO, the receptor 1 shows a greater selectivity towards fluoride. The color of the solution of 1 is changed from colorless to light yellow and finally to yellowish brown only in the presence of fluoride in CH₃CN containing 10% DMSO. In pure DMSO and CH₃CN solvents, almost colorless solution of 1 is transformed into blood red and reddish brown in the presence of 30 equivalent amounts of F^?, respectively.     

Anion-Responsive Fluorescent Supramolecular Gels

Three novel bis-urea fluorescent low-molecular-weight gelators (LMWGs) based on the tetraethyl diphenylmethane spacer—namely, L1, L2, and L3, bearing indole, dansyl, and quinoline units as fluorogenic fragments, respectively, are able to form gel in different solvents. L2 and L3 gel in apolar solvents such as chlorobenzene and nitrobenzene. Gelator L1 is able to gel in the polar solvent mixture DMSO/H₂O (H₂O 15% v/v). This allowed the study of gel formation in the presence of anions as a third component. An interesting anion-dependent gel formation was observed with fluoride and benzoate inhibiting the gelation process and H₂PO₄⁻, thus causing a delay of 24 h in the gel formation. The interaction of L1 with the anions in solution was clarified by ¹H-NMR titrations and the differences in the cooperativity of the two types of NH H-bond donor groups (one indole NH and two urea NHs) on L1 when binding BzO⁻ or H₂PO₄⁻ were taken into account to explain the inhibition of the gelation in the presence of BzO⁻. DFT calculations corroborate this hypothesis and, more importantly, demonstrate considering a trimeric model of the L1 gel that BzO⁻ favours its disruption into monomers inhibiting the gel formation.     

基于含偶氮酚羟基席夫碱新型简单比色传感器

A novel N-(2-hydroxy-5-chlorodibenzophenone)-N0-[2-hydroxy-5-azophenyl-benzaldehyde]-1,2-diaminobenzene receptor has been synthesized by simple steps with good yields. The anion recognition properties were studied by ultraviolet-visible spectroscopy. The resultsshowed that the receptor had a higher affinity to F^-, AcO^-, and H₂PO₄^-, but no evident binding with Cl^-, Br^-, and I^-. Upon addition of the three former anions to the receptors in DMSO, the solution exhibited an obvious color change from colorless to yellow, which could be observed by the naked eye, thus the receptor could act as a fluoride ion sensor even in the presence of other halide ions. The UV-Vis data indicates that a 1:1 stoichiometric complex is formed through hydrogen bonding interactions between receptor and anions.     

About Lanthanoid Fluoride Selenide Oxoselenotantalates with the Composition Ln3F2Se2TaO4 (Ln = La – Nd)

After solid-state reactions of the light lanthanoid metals, their oxides and fluorides as well as selenium in sealed tantalum ampoules with sodium chloride as a fluxing agent at 850 °C for 8 days needle-shaped single crystals of Ln₃F₂Se₂TaO₄ (Ln = La – Nd) were obtained. They crystallize in the orthorhombic space group Pnma analogous to La₃F₂Se₂NbO₄ with a = 1133–1120 pm, b = 400–393 pm and c = 1812–1778 pm (Ln = La – Nd) for Z = 4 as the first known quinary lanthanoid(III) oxoselenotantalates(V) with fluoride and selenide anions. The three crystallographically different Ln³⁺ cations are all surrounded by nine anions (O^2–, F^– and Se^2–) each. Tantalum resides in an octahedral chalcogen coordination by forming trans-vertex oxygen-connected [TaO₅Se]^7– polyhedra, which build up chains ¹_∞{[TaO^V_2/2O^t_3/1Se^t_1/1]^5–} along [010]. The sites of the four crystallographically different oxygen atoms and the two distinct fluoride anions were established by bond-valence calculations. One fluorine and three oxygen atoms are surrounded tetrahedrally by cations, while another fluoride and oxide anion exhibit just triangular non-planar coordination spheres. The two independent Se^2– anions have five or six cationic neighbors.     

Cyanide sensing with organic dyes: studies in solution and on nanostructured Al2O3 surfaces

The synthesis of two new azo phenyl thiourea compounds and their optical response to different anions is reported herein. Solution studies in methanol indicate that cyanide induces a colour change in these dyes (whereas no changes are observed in the presence of other anions, such as F(-), Cl(-), Br(-), CH(3)COO(-), H(2)PO(4) (-), HSO(4) (-)). Interestingly, in DMSO these dyes are responsive not only to cyanide, but also to fluoride, acetate and dihydrogen phosphate. Each of these anions induces a different colour change. In the second part of the paper, we report the attachment of one of these dyes onto nanostructured TiO(2) and Al(2)O(3) films. The stability of these sensitised films to pH was studied and we concluded that the sensitised Al(2)O(3) films are more robust, and hence, better than the TiO(2) for anion sensing. The dye-sensitised Al(2)O(3) films were immersed in solutions of different anions and their response studied. The films can detect cyanide down to 3 ppm in aqueous solution with relatively good selectivity over other anions.     

Novel Chromogenic Chemosensors for Fluoride Anion Based on 8-Hydroxyquinoline Azo Derivatives

A series of 8-hydroxyquinoline azo derivatives with diverse conjugated structures were synthesized and studied to chromogenicaUy detect anions. All the dyes allowed selective detection for fluoride anion in CH3CN via instant deprotonation of the compounds, which was affirmed by UV-Vis absorption and 1H NMR spectra. The chromogenically responding ability increases as the substituent changes from phenyl to naphthyl or anthryl. This result is likely to be related to the enhancement of intramolecular charge transfer （ICT） induced by extension of conjugated structure.