Colorimetric Anion Sensor Research Articles

Spectroscopy and a theoretical study of colorimetric sensing of fluoride ions by salicylidene based Schiff base derivatives

Three colorimetric anion sensors based on salicylidene Schiff bases (salicylaldehyde-o-aminophenol [SA1], 3,5-dimethyl-salicylaldehyde-o-aminophenol [SA2], and 3,5-dichloro-salicylaldehyde-o-aminophenol [SA3] were comprehensively studied based on experimental methods combined with theoretical calculations. All derivatives showed high sensitivity for colorimetric detection of fluoride ions (F−) with a binding stoichiometry of 1:1 in acetonitrile solutions. The color of the sensor solutions visibly changed from light yellow to orange red in the presence of F−. From the experimental results, SA1 and SA2 showed higher potential as F− sensors than SA3 due to their higher selectivity with a limit of detection (LOD) as low as 8 × 10−5, 21 × 10−5 and 7 × 10−5 M, respectively. The optimized structure and electronic transitions were confirmed by DFT and TDDFT studies. In this study, F− detection mechanism is proposed based on experimental and the density functional theory (DFT) calculation.

Carbazole-Based Colorimetric Anion Sensors.

Owing to their strong carbazole chromophore and fluorophore, as well as to their powerful and convergent hydrogen bond donors, 1,8-diaminocarbazoles are amongst the most attractive and synthetically versatile building blocks for the construction of anion receptors, sensors, and transporters. Aiming to develop carbazole-based colorimetric anion sensors, herein we describe the synthesis of 1,8-diaminocarbazoles substituted with strongly electron-withdrawing substituents, i.e., 3,6-dicyano and 3,6-dinitro. Both of these precursors were subsequently converted into model diamide receptors. Anion binding studies revealed that the new receptors exhibited significantly enhanced anion affinities, but also significantly increased acidities. We also found that rear substitution of 1,8-diamidocarbazole with two nitro groups shifted its absorption spectrum into the visible region and converted the receptor into a colorimetric anion sensor. The new sensor displayed vivid color and fluorescence changes upon addition of basic anions in wet dimethyl sulfoxide, but it was poorly selective; because of its enhanced acidity, the dominant receptor-anion interaction for most anions was proton transfer and, accordingly, similar changes in color were observed for all basic anions. The highly acidic and strongly binding receptors developed in this study may be applicable in organocatalysis or in pH-switchable anion transport through lipophilic membranes.

Colorimetric sensor based on hydrazine moiety for rapid and selective detection of fluoride ion via intramolecular charge transfer

ABSTRACT A colorimetric anion sensor (E)-3-((2-((4-(4-Methoxyphenyl)thiophen-2- yl)methyl)hydrazono)methyl)-1 H-indole ATH was synthesised and confirmed by different spectroscopic methods, such as 1 H NMR, 13 C NMR, ESI-Mass and FT-IR spectroscopy. The ATH sensor revealed the spectral change and detection in the presence of fluoride ion over the other anions such as OH−, Cl−, AcO−, I−, HSO4 −, NO3 −, Br−, S2-, CN− & NO2 −. Interestingly, sensor ATH exhibited highly selective fluoride ion detection with significant changes in the colour from light yellow to dark yellow in ACN and ACN: H2O (8:2, v/v) medium. The colorimetric sensor effectively responds to fluoride ion stimulation through deprotonation and (ICT) intramolecular charge transfer sensing mechanism. The fluoride sensing mechanism was confirmed by 1 H NMR titration and was supported by density functional theory (DFT) and electrochemical studies. In this study, the B–H plot calculates the stoichiometry and binding constant (Ka) of the host-guest complex and strong interaction between the probe ATH with fluoride ions forming a 1:2 binding ratio. Furthermore, the test strips based on the probe ATH were used to detect F- ions qualitatively and quantitatively in 100% aqueous solution.

Selective fluoride chemosensors based on coumarin semicarbazones

Twelve (five new) colorimetric anion sensors based on coumarin semicarbazone were studied for selective sensing of fluoride anion. The distinct colour change (by 44–125 nm) under ambient light observed in the Vis region makes the present sensors suitable for naked eye detection of fluoride anion, with detection limit (LOD) 6.6–8.6 ppm for the most sensitive ones. Whereas significant colorimetric changes are observed in the presence of fluoride anion in Me2SO, the commonly competing AcO−, Cl−, Br−, HSO4−, NO2− or NO3− ions induce none or relatively negligible changes. Deprotonation of the semicarbazone NH group is responsible for the sensing event, albeit the mechanism depends on electron density distribution in the coumarin moiety. Quantum chemical calculations suggest several possible geometries for the semicarbazones; the geometry with a hydrogen bond between the hydrazone nitrogen and the NH hydrogen of all of the aniline, cyclohexylamine and aminopyridine fragments, however, results in the most stable structures.

Various Sensing Mechanisms for the Design of Naphthalimide based Chemosensors Emerging in Recent Years

In the design of novel fluorescent chemosensors, investigation of new sensing mechanisms between recognition and signal reporting units is of increasing interest. In recent years, a smart chemosensor probe containing a 1,8-naphthalimide moiety could be developed as a fluorescent and colorimetric sensor for toxic anions, metal ions, biomolecules, nitroaromatics, and acids and be further applied to monitor the relevant biological applications. In this field, several problems and challenges still exist. This critical review is mainly focused on various sensing mechanisms that have emerged in the past few years, such as Photo-Induced Electron Transfer (PET), Intramolecular Charge Transfer (ICT), Fluorescence Resonance Energy Transfer (FRET), Excited-State Intramolecular Proton Transfer (ESIPT), hydrogen bonding and displacement approach. The review concludes with some current and future perspectives, including the use of the naphthalimides for sensing anions, metal ions, biomolecules, nitroaromatics and acids and their potential uses in various fields.

Methyl-3-(2-hidroxy-5-nitrophenyl amino)-3-phenylpropanoate Based Colorimetric Sensor for Oxyanions

A colorimetric anion sensor of methyl-3-(2-hydroxy-5-nitrophenyl amino)-3-phenylpropanoate bearing –OH and –NH groups as binding sites and nitrophenyl as a signaling unit, has been successfully accomplished. The compound functioned as a colorimetric chemosensor for H2PO4– and AcO–, in particular, the sensor showed significant naked-eye detectable color change from colorless to light yellow. In contrast, no color change was detected upon addition of other anions such as SO42–, NO3–, and CIO4–. The anion sensing ability of the sensor was further investigated by UV-Vis absorption spectroscopy in acetone. Characteristic UV-Vis spectra changes were revealed upon addition of H2PO4– and AcO–.

Dyes based on the 2(1H)‐quinolone skeleton as potential colorimetric and fluorescent sensors for cyanide anions

AbstractThe sensing properties of dyes based on 2(1H) quinolones containing dicyanoethylene groups towards selected anions such as CN−, F−, I−, Cl−, SCN−, CH3COO−, and were evaluated. The spectroscopic responses of these compounds were investigated in a solution of acetonitrile/water (1:9, v/v) and phosphate buffer at a pH of 7.4. These dyes were found to act as efficient colorimetric and high turn–off fluorescent sensors to cyanide anions. The fluorescence intensity was linearly related to the concentration of CN− from 1 to 10 µmol/L, and the detection limits reached a micromolar level of 6.7, 11.1, 3.8 and 7.2 µmol/L for 1‐4, respectively. The cytotoxic effect of the dyes against human neuroblastoma cells (SH‐SY5Y) was also determined by MTT assay. The examined compounds exhibited slight cytotoxicity against cells under experimental conditions.

Schiff base derived from salicylaldehyde‐based azo dye as chromogenic anionic sensor and specific turn‐on emission sensor for cyanide ion

AbstractA novel Schiff base has been derived from condensing 4‐aminoantipyrine with diazotized salicylaldehyde. The derived compound acted as a colorimetric sensor for hazardous aqueous anions like CN−, F−, and CH3COO− among a list of anions. The colorimetric changes were further verified through absorption titrations. The detection limits were of the order of 10−10 M, which makes the sensor significant. The interaction of the anions with the sensor was stoichiometrically 1:1 with good binding constants. The sensor turns out to be a specific turn‐on emission sensor for CN− even in competitive environments. The F− ion sensing ability was extended to the determination of F− in a commercial toothpaste with good results.

Naked Eye Detection of Carbonate, Hydroxide, and Cyanide Ions with 1,4′‐Diazaflavonium Bromides: A Simple Spectrophotometric Method for Cyanide Determination

Anion sensor properties of N‐alkyl‐substituted 1,4′‐diazaflavonium bromides in methanol–water were evaluated by UV–vis spectrometry. Pronounced changes were observed in the absorption spectra of all compounds for only OH−, CO32−, and CN− among F−, Cl−, Br−, I−, OH−, CO32−, NO3−, PO43−, CN−, SO42−, HSO4−, HCO3−, SCN−, NO2−, and P2O72− ions. Two new absorption bands at 385 and 685 nm accompanying the distinct color change for OH−, CO32−, and CN− ions were observed in case of all compounds. The color changes were from pink to blue for CO32− and OH− ions and from pink to purple for CN− ion. Thanks to the distinct color change, the compounds can be used as selective colorimetric anion sensors. Linear changes of absorbance of N‐heptyl‐substituted compound at 385 nm as a function of the ion concentration were used to determine CN− ion in water samples. Detection and quantification limits of the proposed method were 0.94 and 2.82 mg/L, respectively.

Addition of α-Cyanomethylpyridine to Naphthalimide via Trifluoromethyl-Directed CH Functionalization: Cyanide Sensing in Aqueous Media.

A colorimetric anion sensor based on the activated C-H group is described, and the selective and reusable detection of cyanide using the sensor is demonstrated. The system uses bromine to block isomerization and trifluoromethyl-directed C-H regioselective functionalization for direct C-C bond formation between a fluorophore and 2-(pyridin-2-yl)acetonitrile. Thus, this system provides a new way to develop activated CH-based anion receptors.

Synthesis, Crystal Structure, Anion Sensing Applications and DFT Studies of (E)-2-[(3,5-Bis(trifluoromethyl)phenylimino)methyl]-4-chlorophenol

We report the synthesis and characterization, colorimetric anion sensors properties, density functional theory (DFT) calculation studies of a Schiff base (E)-2-[(3,5-bis(trifluoromethyl)phenylimino)methyl]-4-chlorophenol. The molecular structure of the title compound was experimentally determined using X-ray single-crystal data and was compared to the structure predicted by theoretical calculations using DFT. The experimental and calculated data (using DFT) of the title compound have been compared. To investigate the tautomeric stability, some properties such as total energy, HOMO and LUMO energies, the chemical hardness (η), the ionization potential, the electron affinity, the absolute electronegativity (χ), the absolute softness (σ) of the compound were obtained at B3LYP/6–311++G(d,p) level in the gas phase and solvent phase. The calculated results showed that the enol-imine form of the compound was more favorite than keto-amine form. The colorimetric response of the Schiff base receptors in DMSO was investigated.

Chalcone Based Colorimetric Sensor for Anions: Experimental and TD-DFT Study

The interactions between sensor chalcone of 3-(4-hydroxy-3-methoxyphenyl)-1-phenyl-2-propen-1-one (1) and anions (F–, Cl–, Br–, CN–, CO32–, and SO42–) have been experimentally and TD-DFT theoretically investigated. Sensor (1) showed a naked-eye detectable color change from yellow to red upon addition of F–, CO32–, CN–, and SO42– anions in DMSO, whereas no significant color change was observed upon addition of Cl– and Br– anions. The interaction models were predicted by optimizing (1)-anion complex using DFT/B3LYP method. Optimized (1)-anion complexes showed that sensor (1) was deprotonated by CO32–, CN–, F–, and SO42–. The formation of deprotonated sensor (1)– was responsible for the colorimetric signaling. Absorption spectra of neutral and deprotonated sensor were calculated using TD-DFT method. The calculated spectra were in good agreement with experimental results.

A reusable cyanide sensor via activation of C-H group: trifluoromethylcarbinol-directed meta-C-H cyanomethylation of naphthalimide.

A fluorescent and colorimetric anion sensor based on the activated C-H group has been developed, and its reusability and ability to selectively detect cyanides have been demonstrated. The system utilizes trifluoromethylcarbinol-directed C-H regioselective cyanomethylation for direct C-C bond formation between the fluorophore and acetonitrile. The present paper also describes a novel strategy for the enhancement of carbanion stability by a potential intramolecular C[double bond, length as m-dash]OH-C hydrogen bonding system, thus providing a new way to develop activated CH-based anion receptors.

Colorimetric anion sensors based on positional effect of nitro group for recognition of biologically relevant anions in organic and aqueous medium, insight real-life application and DFT studies

A new six colorimetric receptors A1-A6 were designed and synthesized, characterized by typical common spectroscopic techniques like FT-IR, UV–Visible, 1H NMR, 13C NMR and ESI-MS. The receptor A1 and A2 exhibit a significant naked-eye response towards F− and AcO− ions in DMSO. Due to presences of the NO2 group at para and ortho position with extended π-conjugation of naphthyl group carrying OH as a binding site. Compared to receptor A2, A1 is extremely capable of detecting F− and AcO− ions present in the form of sodium salts in an aqueous medium. This is owed to the occurrence of NO2 group at para position induced in increasing the acidity of OH proton. Consequently, it easily gets deprotonated in aqueous media. The detection limit of receptor A1 was turned out to be 0.40 and 0.35ppm for F− and AcO− ions which is beneath WHO permission level (1.0ppm). Receptor A1 shows a solitary property of solvatochromism in different aprotic solvents in presence of AcO− ion. Receptor A1 depicts high selectivity towards AcO− ion in DMSO: HEPES buffer (9:1, v/v). Receptor A1 proved itself for real life application by detecting anion in solution and solid state. The binding mechanism of receptor A1 with AcO− and F− ions was monitored from 1HNMR titration and DFT study.

Bis(pyrrole-benzimidazole) conjugates as novel colorimetric sensor for anions

Novel bis(pyrrole-benzimidazole) (PYBI) conjugates were investigated as colorimetric anion recognition motif by employing multiple donor sites. In this regard, PYBI derivatives where pyrrole unit is connected to the C2 position of benzimidazole via its $$\alpha $$ -position were synthesized and their anion recognition behavior were evaluated by UV-Vis, fluorescence and $$^{1}\hbox {H NMR}$$ spectroscopy. PYBI selectively interacts with fluoride ion, whereas introduction of nitro group on the benzimidazole moiety enhances the binding affinity by at least one order, albeit at the expense of the selectivity. Bridging of two PYBIs led to interesting cooperative effect between the two subunits, which gets enhanced upon changing the spacer between the two from non-conjugating type $$({ sp}^{3}\hbox {-C})$$ to conjugating one (quinoxaline). This also affects the way they interact with anions, with the latter moiety displaying very interesting stepwise double deprotonation of benzimidazole protons upon addition of fluoride ions with strong colorimetric as well as fluorometric response. Further, acidity of the H-bond donor sites was found to play pivotal role in the anion complexation mechanism and selectivity. SYNOPSIS Novel bis(pyrrole-benzimidazole) (PYBI) conjugates where pyrrole units are connected to the C2 position of benzimidazole via its $$\alpha $$ -position were synthesized and their anion recognition behavior were evaluated. Anion selectivity and mode of interaction was found to depend on the nature of the substituent and the spacer between the two PYBI units.

An NIR Molecule-based “On–Off” Fluorescent and Colorimetric Sensor for Cyanide Anions

A simple triphenylamine-based molecule P2 was developed as a near-infrared (NIR) “on–off” fluorescent and colorimetric sensor to detect cyanide anions. The nucleophilic attack of cyanide (CN−) onto...

Cysteine-based silver nanoparticles as dual colorimetric sensors for cations and anions

The synthesis of amide–triazole-based Ag NPs and their sensing ability towards anions and cations in aqueous solution were investigated. The importance of amide–triazole as a binding motif, in conjunction with Ag NPs, and the mode of the sensing ability of these amide–triazole Ag NPs as dual colorimetric sensors have been studied in detail.

Acylthiourea derivatives as colorimetric sensors for anions: Synthesis, characterization and spectral behaviors

Several acylthioureas have been synthesized to develop colorimetric sensors for detection of biologically important anions. UV–vis titration experiments indicated that the absorbance values have a good linear relationship with concentration of anions when the anions were added in AR-1, AR-4 and AR-6 sensor molecules. The detection limit to AcO− and F− is 5×10−6mol/L when the concentration of receptors are 2×10−5mol/L. Especially, compounds AR-1 and AR-4, decorated with strong electron-withdrawing NO2 substituent, showed augmented anion sensing properties, being capable of naked-eye detecting of F− and AcO− when the water content is lower than 15%. The recognition details of anion sensing were also assessed using 1H NMR technique and confirmed that the basic anions induced deprotonation of N–H.

Substituent effects on anion sensing of salicylidene Schiff base derivatives: Tuning sensitivity and selectivity

A series of colorimetric anion sensors using the salicylidene Schiff bases with different substituents, including electron donating group (tert-butyl, in sensor 2), conjugated group (naphthyl, in sensor 3) and electron withdrawing group (chlorine, in sensor 4), respectively, have been developed. The substituents can not only impact chromogenic signal output, but also tune the sensitivity and selectivity of the anion sensing by their specific electron push–pull features. In particular, both 1 (without substituent) and 2 show high selectivity for F− over Cl−, Br−, I−, AcO− and H2PO4−, but the sensitivity of 2 is poorer than 1 due to the effect of electron donating groups. Sensor 3 exhibits higher sensitivity for F− than 1, but it is disturbed by the weak response to AcO− and H2PO4−. Sensor 4 has the highest sensitivity for F−, but shows the significant response to AcO− and H2PO4−, which also decreases the selectivity for F−. Finally, analytical applications of 1 for the detection of F− in aqueous medium and toothpaste have been studied.

An Amide-Functionalized Dynamic Metal-Organic Framework Exhibiting Visual Colorimetric Anion Exchange and Selective Uptake of Benzene over Cyclohexane.

A novel porous metal-organic framework (MOF) architecture is formed by a neutral amide-functionalized ligand and copper(II). Upon desolvation, this compound undergoes a dynamic structural transformation from a one-dimensional (1D) porous phase to a two-dimensional (2D) non-porous phase that shows selective uptake of benzene over cyclohexane. The as-synthesized compound also acts as a visual colorimetric anion sensor for thiocyanate.