Colorimetric Anion Research Articles

UV-Vis spectroscopic and colorimetric anion detection and fluorescence properties of new 3-amino-4-hydroxybenzenesulfonic acid-based Schiff bases depending on the strength and position of the electron donor substitution

In this study, 3-amino-4-hydroxybenzenesulfonic acid-based imine compounds; 3-(2,5-dihydroxybenzylideneamino)-4-hydroxybenzenesulfonic acid (1), 3-(2,4-dihydroxybenzylideneamino)-4-hydroxybenzenesulfonic acid (2) and 4-hydroxy-3-(2-hydroxy-3-methoxybenzylideneamino)-4-hydroxybenzenesulfonic acid (3) was synthesized. The compounds were analyzed using various spectroscopy methods, and the experimental UV–vis data matched the theoretical predictions. The compound 1 displayed lower stability, higher reactivity, and easier photoexcitation due to a smaller HOMO-LUMO energy gap. The investigated compounds 1-3 showed promise as chemosensors for anions, providing visible detection in daylight conditions. The compound 3 exhibited selective fluorescence at specific wavelengths. The compounds 1-3 interacted with DNA through electrostatic interactions. Also, compounds 1-3 showed higher antioxidant activity than BHT. However, fluorescence measurements indicated that the emission signals were strongly influenced by the position and strength of the electron-donating group. Adding a hydroxy or methoxy moiety near the -OH group on the phenyl ring decreased the fluorescence signal due to intersystem crossing and intramolecular charge transfer mechanisms, respectively. These findings were supported by femtosecond transient absorption spectroscopy measurements. The results emphasize the significance of substituents in imines derived from 3-amino-4-hydroxybenzenesulfonic acid in determining their biological activities, as well as their optical and sensor properties.

Light-up, colorimetric anion sensing and fingerprint visualization using the salicylaldehyde-based aggregation-induced emission-active phosphorescent Pt(II) complexes formed by restricting the molecular configuration transformations

Developments of the AIE phosphorescent metal complexes are behind to these of pure organic AIEgens. Herein, Two AIE-active phosphorescent Pt(II) complexes applicating in anion detection and fingerprint visualization are reported. The distinct emission differences between dilute solutions and aggregated states manifest their AIE natures, supporting by the THF-H2O and film emission measurements. Importantly, it demonstrates that molecular configuration transformation (MCT) from the square planarity to the tetrahedron and the intramolecular rotation induce non-radiations of S1 and T1 states, thus almost no emissions of their dilute solutions. Upon aggregation or in rigid environment, the MCT and intramolecular rotation are restricted by themself or the matrix, radiative decays of excited states are aroused in aggregated or film states. Considering the acidity of the –OH unit in salicylaldehyde group, these complexes towards to fluoride ion detections including the naked-eye UV–Vis and light-up emission responses, anti-interference abilities, stoichiometry of 2 : 1, 10−7 M detection limits, deprotonation sensing mechanism and real sample test are fully covered and deeply investigated. Taking advantages of AIE natures, they are applicated in fingerprint detections featuring the fast speed, high resolution and multi-level characters. Eventually, the obtained results should expectedly offer valuable clues for phosphorescent AIE-active metal complexes and related application developing.

A molecular tuner: Substituent controlled π/π···hole induced selective colorimetric intramolecular push-pull fluoride sensor

Controlling the anion selectivity of synthetic anion receptors towards a particular anion is challenging task for researcher. In the case of bipodal receptors this become trickier since anion can approach the recognition elements of receptors from any direction. In order to overcome this problem, we adopted the new strategy in which the receptor molecules are functionalized with electron donating and/or withdrawing group. In the way of hunting such a receptors, herein Thio-semicarbazide based chemosensors 1-(2,4-dinitrophenyl)-4-(4-nitrophenyl) thiosemicarbazide L1, and 1-(2,4-dimethylphenyl)-4-(4-nitrophenyl) thiosemicarbazide L2 with electron withdrawing (EW) and donating (ED) groups have been synthesized for selective colorimetric anion sensing. Substituent effects on the strength of those receptors L1 and L2 have been studied by naked-eye colorimetric experiments, Ultraviolet-Visible (UV-Vis) spectrometric titration studies, Fourier-Transform Infrared experiments (FT-IR), 1H-NMR, 19F-NMR spectroscopic studies and Molecular Electrostatic Potential (MEP) surface analysis. When we have nitro substitution on both end of the thio-semicarbazide receptor L1, there were no selectivity was found with anions and receptor L1 shows visible color change with the all the tested anions. On the other hand, instead of nitro, when we have methyl substitution on one end and nitro substitution at an another end of the thio-semicarbazide receptor L2, then the receptor L2 show excellent selectivity towards fluoride ion with high association constant. Additionally, for azide considerable bathochromic shift of 70 nm also observed with reference to absorption values of cyanide and fluoride anion which will clearly distinguish the presence of azide ion from cyanide and fluoride. The observed bathochromic shift is mainly attributed due to the intramolecular charge transfer (ICT). In this work, we have successfully tuned the selectivity of synthesized receptors via generating a push-pull effect originated by electron withdrawing and donation substitutions on both end of the receptor L2. The enhanced selectivity of L2 is achieved by altering the acidity of -NHs of thio-semicarbazide derivative L2 by substituting EW and ED groups. In this present work, we have tuned the selectivity of receptor is via intramolecular push-pull effect by electron withdrawing and donating substituent.

Naked-eye colorimetric anion probing and fluorescent switching features of conjugated Schiff Bases derived from 4-(Trifluoromethyl) benzenesulfonamide

In this work, synthesis, spectroscopic, density functional theory (DFT) and photophysical studies of the three conjugated benzenesulfonamide Schiff bases were reported. We also calculated the energies of the frontier molecular orbitals (FMOs) and UV–Vis spectra of Schiff bases theoretically using the DFT and TD-DFT methods. Additionally, photophysical properties were investigated by UV–Vis and fluorescence spectroscopy techniques. The ground state interactions show that the absorption band has been separated into two branches and bathochromatically tuned to the visible region, and fluorescence intensity decreased in the case of the Schiff base incorporated naphthalene unit. Furthermore, the charge transfer dynamics of the compounds were analyzed using femtosecond transient absorption spectroscopy measurements proving the triplet-triplet transitions via intersystem crossing mechanism. Based on the ultrafast pump-probe experimental results, as well as decay kinetics of the compounds, the Schiff base with naphthalene unit, showed a fast transition to the triplet state (1.2 ps) as compared to Schiff bases including methyl (4 ps) and chloro (2.7 ps) units. However, upon the addition of various anions, the molecule structure gains anion sensing and fluorescence switching capabilities under daylight and UV light. The obtained experimental results pointed out that the modification of Schiff base molecules with methyl, chlorine and naphthalene units affected its photophysical properties as well as excited-state dynamics significantly.

Colorimetric probe and optical behaviours of new azomethine derivatives of sulfonamide

Syntheses, colorimetric anion probe properties, density functional theory (DFT) studies, and optical properties of the Schiff bases; 4-fluoro-N-(2-hydroxy-5-methylbenzylidene) benzenesulfonamide (1), 4-fluoro-N-(2-hydroxy-5-nitrobenzylidene)benzenesulfonamide (2) and 4-fluoro-N-[(2-hydroxynaphthalen-1-yl)methylene]benzenesulfonamide (3) were reported. The structure of the compounds was elucidated using MS, FTIR, and UV-visible spectroscopic techniques. Their structures were examined by theoretical calculations using density functional theory (DFT). The colorimetric response of the Schiff base receptors in DMSO was investigated before and after the addition of an equivalent amount of each anion to evaluate the anion recognition properties. The ultrafast transient absorption spectroscopy measurements were performed to investigate the energy transfer dynamics and decay kinetics of the compounds 1-3. The fluorescence and wavelength-dependent pump-probe measurements of the compounds showed that the excited state lifetime of compound 2 is shorter than compounds 1 and 3. The fluorescence properties of compounds 1-3 were compatible with the pump-probe spectroscopy measurements. The compounds with longer ESA lifetimes showed higher fluorescence.

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.

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–.

Novel use of calmagite as a fast and easy colorimetric anion chemosensor and solid-state sensor for carbonate ion in running water

ABSTRACT This experiment studies the use of an available azo dye, calmagite (CAL), for the recognition of carbonate ion in running water. The linear range of carbonate, derived from the results of this simple, selective, sensitive and rapid determination, was 1.2 × 10−8–5.4 × 10−6 mol L−1 with the detection limit of 1.6 × 10−8 mol L−1. In the examined cases, the coexisting cation, anions and weak acids (NO3 −, NO2 −, SO4 2−, SO3 2−, HSO3 −, OAc−, I−, Br−, F−, Cl−, SCN−, CO3 2−, HCO3 −, H2PO4 −, HPO4 2−, Cit3−), (Ascorbate, K+, Na+, Mg2+ <6.9 × 10−4 mol L−1) did not restrict the analysis by causing interference. The recoveries which were in the range of 97.3–101.4% established the evidence of the validity of the method for real water samples. The obtained results manifested good proof of the accuracy of the method to be comparable with acid-base titration. In general, the method was cost-effective and fast, with the uncomplicated operation, which made the receptor suitable for rapid detection of carbonate ion in freshwater in the field. On the other hand, having regard to the modifications calmagite made in the filter paper strips, this chemosensor revealed the great potential to be applied as a carbonate solid-state colorimetric indicator.

Triazole derived azo-azomethine dye as a new colorimetric anion chemosensor.

In the pursue of developing anion sensors, an efficient triazole derived azo-azomethine dye chemosensor (S) that differentially senses F‾ and AcO‾ ions has been reported. The ions recognition ability of S was investigated by colorimetric and UV-visible spectroscopic methods. Interestingly, this chemosensor molecule is virtually inactive in presence of other anions such as Cl‾, Br‾ and I‾ and HSO4‾. We have further presented a ratiometric approach to differentiate F‾ and AcO‾ ions. The reversibility of F‾ ion binding with S was established by the addition of Ca(NO3)2 to the fluoride bound S, which led to the regeneration of S. The quantum chemical calculation of energies of unbound and bound S has been employed using Density Functional Theory (DFT) to understand the interaction between chemosensor and anions. Evidence in support of fluoride-induced deprotonation of a O-H bond during the detection of F⁻ ion has been demonstrated by employing 1H NMR titration experiments.

Design and synthesis new colorimetric receptors for naked-eye detection of biologically important fluoride and acetate anions in organic and arsenite in aqueous medium based on ICT mechanism: DFT study and test strip application.

Novel three colorimetric anion receptors R1, R2 and R3 have been designed and synthesized via condensation reaction and characterized using IR, MS, and NMR spectroscopic techniques. Anion sensing properties were studied using colorimetric, UV-vis titration, 1H NMR titration, and Cyclic Voltammetric Studies. Comparing the UV-visible titration data of the receptors R1 and R2, R2 showed high redshift (∆λmax) in the mixed competitive solution (DMSO: H2O, 9: 1; v/v) of about 155 nm, 157 nm, 169 nm for Na+F-, Na+AcO-, and Na+AsO2- ions with LOD of 0.23 ppm, 0.18 ppm, and 0.30 ppm, respectively. The observed spectral change of receptor R2 is due to the anion-induced deprotonation of the OH proton, which is confirmed by UV-vis titration, 1HNMR titration, and cyclic voltammetric studies. Theoretical studies via DFT calculation were carried for R1 and R2 to optimize the structure and to explain the anion-binding mechanism. The application of designed receptor R2 was successfully demonstrated for the detection of F- and AsO2- ions using a test strip. The receptors R1 and R2 proved itself to be potentially useful for real-life application by sensing F- and AcO- ions in real samples like toothpaste, mouthwash, vinegar and seawater in a complete aqueous medium.

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.

Rapid detection of HSO4− in water: Novel immobilized azo-azomethine colorimetric anion receptors on solid supports

The immobilized azo-azomethine receptors on amorphous SiO2, S-B, SiO2 nanoparticles, S-NPs, and NaY zeolite, S-ZY, have been prepared and applied as solid phase sensors for detection of HSO4−, over other interfering anions, in 100% aqueous media. Remarkably, S-B and S-ZY show unique and rapid sensitivity towards HSO4−, which could it easily visualized through naked eye detection even at 5×10−4molL−1 and 4×10−4molL−1, respectively. The fabricated solid phase sensors were characterized using powder XRD diffraction, TGA-DTA, FE-SEM and also FT-IR techniques. Moreover, the related molecular anion receptor, HL, has been prepared and used for naked eye detection of F− and AcO−, in dry DMSO. The anions recognition ability of HL was also evaluated using UV–Vis and 1H NMR spectroscopic methods.

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.

Electroanalytical and spectral investigation of organic receptors as colorimetric and absorption ratiometric anion chemosensor

Colorimetric receptors R1 and R2 have been designed and synthesized by Schiff base condensation and characterised by standard spectroscopic techniques. Anion binding ability of the receptors have been investigated quantitatively through optical, electrochemical and 1HNMR titration studies. UV-vis spectra of receptor R1 and R2 exhibited a significant red shift for F− and AcO− ions with a visual color response. Receptor R1 exhibited selective response towards AcO− ion in the presence of HEPES buffer media. Incremental color change of receptor R2 with the higher equivalence of AcO− ions clearly represent the ratiometric response. Cyclic voltammetric studies of R1 and R2 exhibits shift in oxidation and reduction peak with successive addition of AcO− ions indicating the anion induced oxidation of -NH and reduction of the keto group and nitro species. Electrooptical and 1H NMR titration studies of R2 collectively reflects the anion induced change of chromophore from C=N to N=N indicative of azo-hydrazone tautomeric signaling in the presence of AcO− ions. Lower detection limit of 2.1 and 0.41 ppm achieved with sodium salt of AcO− ion with R1 and R2 reflects their utility as colorimetric chemosensor.

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.