Fluorogenic Chemosensor Research Articles

Simple salicylaldimine-functionalized dipodal bis Schiff base chromogenic and fluorogenic chemosensors for selective and sensitive detection of Al3+ and Cr3+

Two salicylaldimine-functionalized dipodal bis Schiff base low cost fluorescent colorimetric chemosensors L1 (bis([4-(2-hydroxy-3-methoxybenzyl-ideneamino)phenyl]ether) and L2 (di[(4-phenylimino)4-diethylsalicyl-aldehyde]ether) have been designed and synthesized. These sensors could simultaneously detect two biologically important metal ions (Al3+ and Cr3+) by change in both absorption and fluorescence intensity in CH3CN-H2O (1/1, v/v) solvent mixture at physiological pH. The jobs plot analyses indicate the 2:2 binding stereochemistry for Al3+ and Cr3+ ions with both the probes L1 and L2, which were further been confirmed by 1H NMR and ESI-MS studies. The binding constant values for L1 were found to be 2.35 × 105 M−1 for Al3+ and 1.26 × 105 M−1 for Cr3+ and in case of L2 these values are 1.46 × 105 M−1 for Al3+ and 3.0 × 105 M−1 for Cr3+. The detections limits of the sensor L1, for Al3+ (1.73 × 10−7 M) and Cr3+ (1.12 × 10−7 M) and of the sensor L2, for Al3+ (4.34 × 10−7 M) and Cr3+ (7.73 × 10−7 M) are far below than the limit set by the World Health Organization (WHO) for drinking water. Moreover, visible colorimetric test kits and real samples for rapid detection of Al3+ and Cr3+ could be successively applied for all practical purposes, indicating their potential use in environmental samples.

Aggregation-induced emission–based highly selective ‘turn-off’ fluorogenic chemosensor for robust quantification of explosive picric acid in aqueous and solid states

An exclusive fluorescent probe, N,N′-di-[2-hydroxy-3-methoxy-benzylidene]-benzene-1,4-diamine (DBA), has been well designed and synthesized. Intriguingly, it displayed attractive aggregation-induced emission (AIE) phenomenon in aqueous media. Based on its interesting AIE characteristic, the fluorescent hydrosol has been used as a sensor with swift sensitivity and excellent selectivity toward nitro-explosive picric acid (PA) and the limit of detection (LOD) as low as 72 nM and 2.3 ng in aqueous and solid states, respectively. The recognition event occurs absolutely within 10 s after the addition of PA, demonstrating a promising ‘zero-wait’ recognition method. Fluorescent paper strips were prepared for instant trace recognition of PA by naked eye in solid state, making the protocol fast, inexpensive, and practical for on-site solid-state detection.

On the Aggregation and Sensing Properties of Zinc(II) Schiff-Base Complexes of Salen-Type Ligands.

The zinc(II) ion forms stable complexes with a wide variety of ligands, but those related to Schiff-bases are among the most largely investigated. This review deals with the peculiar aggregation characteristics of Zn(II) Schiff-base complexes from tetradentate N2O2 salen-type ligands, L, derivatives from salicylaldehydes and 1,2-diamines, and is mostly focused on their spectroscopic properties in solution. Thanks to their Lewis acidic character, ZnL complexes show interesting structural, nanostructural, and aggregation/deaggregation properties in relation to the absence/presence of a Lewis base. Deaggregation of these complexes is accompanied by relevant changes of their spectroscopic properties that can appropriately be exploited for sensing Lewis bases. Thus, ZnL complexes have been investigated as chromogenic and fluorogenic chemosensors of charged and neutral Lewis bases, including cell imaging, and have shown to be selective and sensitive to the Lewis basicity of the involved species. From these studies emerges that these popular, Lewis acidic bis(salicylaldiminato)Zn(II) Schiff-base complexes represent classical coordination compounds for modern applications.

Turn-on Fluorescence Chemosensor for Zn2+ Ion Using Salicylate Based Azo Derivatives and their Application in Cell-Bioimaging.

The synthesis and optical studies of salicylate based azo derivatives (DPSAD and IPSAD) are reported. The receptors act as a versatile fluorogenic chemosensor for Zn2+ causing a selective enhancement of fluorescence over other competing cations. The complex formed between receptors and Zn2+ are identified on the basis of absorption and fluorescence titration and further confirmed by ESI-MS. DFT/TD-DFT calculations support the observed optical changes happens only upon complexation with Zn2+ ion. Moreover, receptors are further applied to intracellular sensing and imaging studies. Graphical Abstract Salicylate based azo derivatives (DPSAD and IPSAD) as fluorogenic chemosensor for the detection of Zn2+ ion.

Highly selective turn-on fluorogenic chemosensor for Zn2+ based on chelation enhanced fluorescence

A new fluorescent zinc sensor was constructed based on cyclic and noncyclic Schiff's bases obtained by the condensation of 4‑(diethylamino) salicylaldehyde and 2‑aminobenzenethio under two different catalytic conditions such as sulphuric acid yields 2‑(benzo[d]thiazol‑2‑yl)‑5‑(diethylamino) phenol (L1) and acetic acid gives to (E)‑5‑(diethylamino)‑2‑(((2‑mercaptophenyl)imino)methyl) phenol (L2). Both L1 and L2 alone exhibits a week fluorescence in CH3OH/H2O (1:1, v/v) due to excited state intra-molecular change transfer (ESIPT) process but upon interaction with Zn2+ shows strong fluorescence due to chelation-enhanced fluorescence (CHEF) but with selected metal ions, there is no such a fluorescence change was observed. The Job's plot and B-H plot studies were revealed the formation of 2:1 and 1:1 stoichiometry with an estimated association constant (Ka) of 4.9 × 104 M−1 and 2.1 × 104 M−1 with L1 and L2 respectively. The detection limit of both sensors L1 and L2 were found to be 6.7 × 10−8 M and 3.6 × 10−7 M respectively. The fluorescence reversibility study was done by adding Zn2+ and EDTA sequentially to L1 and L2. Both sensors were successfully used for the determination of Zn2+ in the different water samples and pharmaceutical multivitamins tablet. The sensing mechanism was studied by 1H NMR, ESI-mass analysis as well as theoretical calculations using the Gaussian 09 program.

Naked-eye chromogenic and fluorogenic chemosensor for mercury (II) ion based on substituted distyryl BODIPY complex

One kind of novel distyryl substituted BODIPY-based fluorescent chemosensor 2 for Hg2+ ion sensing has been reported. Large hypsochromic shift of the absorption band is observed upon titration with Hg2+ ion resulting in a solution color change from green to light yellow, enabling “naked-eye” detection possible. Meanwhile, the fluorescence intensity of 2 around 680 nm was quenched upon adding Hg2+ ion due to the blocking of the ICT process. Most importantly, chemosensor 2 exhibits high selectivity and sensitivity towards Hg2+ ion over other metal ions in aqueous solutions.

Colorimetric and Fluorogenic Chemosensors for Mercury Ion Based on Nanomaterials

Colorimetric and Fluorogenic Chemosensors for Mercury Ion Based on Nanomaterials

Sequential detection of Cu2+ and cysteine using an imidazole‐based chemosensor in aqueous solution

A highly substituted imidazole‐based colorimetric and fluorogenic chemosensor, 2‐methoxy‐4‐(4,5‐diphenyl‐1H‐imidazol‐2‐yl)phenol (L), for the detection of Cu2+ ion and subsequent colorimetric detection of an amino acid, cysteine, was investigated. L exhibited a distinct color change from colorless to red in the presence of Cu2+ in an aqueous medium. The L‐Cu2+ complex can also be used to detect cysteine by the naked eye over a series of amino acids. The receptor L behaves as a highly selective colorimetric and fluorescent sensor for Cu2+ ions at concentrations as low as 4.33 and 2.25 μM, respectively. These values are much less compared to the WHO recommended limit of 30 μM for Cu2+ in drinking water. From Job's plot and the ESI‐MS spectrum, a 1:1 stoichiometric complex between L and Cu2+ ions can readily be reckoned. This binding was also substantiated by the EPR spectrum and magnetic susceptibility measurements. Additionally, the binding of L with Cu2+ ions was also manifested in the detection of B16F10 cells. This was substantiated through fluorescence microscopy. The spectrum of the L‐Cu2+ entity was also attempted to reproduce theoretically. The probable structure of this was also propounded through Density Functional Theory.

Functionalized Quinoxaline for Chromogenic and Fluorogenic Anion Sensing.

This Review article provides a comprehensive analysis of recent examples reported in the field of quinoxaline‐based chromogenic and fluorogenic chemosensors for inorganic anions such as fluoride, cyanide, acetate, and phosphate, as well as their utility in biomolecular science. It commences with a discussion of the various structural motifs such as quinoxaline‐based oligopyrroles, polymers, sulfonamides, cationic receptors, and miscellaneous receptors bearing mixed recognition sites in the same receptor. Advances are discussed in depth, where the focus of this review is to tackle mainly solution state anion sensing utilizing quinoxaline‐based receptors using different spectroscopic techniques with reference to anion selectivity by colorimetric and fluorescence response. The various examples discussed in this Review illustrate how the integration of anion binding elements with the quinoxaline chromophore could result in anion responsive chemosensors. Over the years, it has been observed that structural modification of the quinoxaline moiety with different sets of signaling unit and recognition sites has resulted in a few anion specific chemosensors.

A new fluorene derived Schiff-base as a dual selective fluorescent probe for Cu2+ and CN.

A new fluorene based fluorogenic chemosensor, 2-[(9H-Fluoren-2-ylmethylene)-amino]-phenol (L), has been designed, synthesized, and characterized by CHN analyses and different spectroscopic methods. This turn-on fluorogenic chemosensor shows high selectivity and sensitivity toward Cu2+ and CN- with low detection limits of 1.54 × 10-9 M and 1.83 × 10-7 M, respectively. The stoichiometry ratio of L-Cu2+ in solution is 1:1, by the method of Job's plot and ESI-MS. The microcrystalline solid product of the chemosensor reaction with copper is characterized as CuL2. The χT value for CuL2 is temperature independent at a value of 0.403 cm3 K mol-1, which is in agreement with a mononuclear copper(II) complex with an isotropic g-value of 2.075. The fluorescence turn-on recognition process for detection of Cu2+ is attributed to the restricted imine isomerization and blocking of intramolecular charge transfer (ICT) quenching process in the analyte-bound sensor. The selectivity of L for Cu2+ is based on the chelation-enhanced fluorescence effect (CHEF) mechanism. Other interfering ions such as Na+, K+, Ca2+, Mg2+, Ag+, Fe2+, Fe3+, Co2+, Ni2+, Zn2+, Cd2+, Hg2+, Mn2+, Pb2+ and Al3+, show no change in the fluorescence intensity of L in the presence of Cu2+. Furthermore, the compound L can be used as a fluorescence and colorimetric sensor for selective detection of CN- over a number of other anions based on the nucleophilic addition to the imine CN bond, with consequent hydrogen bond formation and electrostatic interaction of the resulting product with K+. The sensing mechanism for CN- was theoretically supported by DFT calculations.

A New Highly Selective Chromogenic and Fluorogenic Chemosensor for Copper (II)

Fil: Quindt, Matias Ivan. Universidad Nacional del Litoral. Instituto de Quimica Aplicada del Litoral. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Quimica Aplicada del Litoral.; Argentina

Photo- and Ionochromic Spiroindoline-2,2′-pyrano[2,3-f]chromenecarbohydrazides—Chemosensors for Lanthanide Cations

Photochromic indoline spiropyrans with carbohydrazide substituents in the pyrano[2,3-f]chromene moiety of the molecule have been synthesized. These compounds exhibit inochromic properties and are chromogenic (“naked-eye”) and fluorogenic chemosensors for lanthanide cations.

Combined use of spectrophotometer and smartphone for the optical detection of Fe3+ using a vitamin B6 cofactor conjugated pyrene derivative and its application in live cells imaging

Synthetically easy, a new chemodosimeter-type chromogenic and fluorogenic chemosensor L was developed by condensing 1-aminopyrene with the vitamin B6 cofactor pyridoxal for the selective detection of Fe3+. Receptor L exhibits a rapid colorimetric response from yellow to colourless and a distinct fluorescence enhancement at 441 nm with Fe3+ due to the cleavage of imine linkage. The optical responses from L in the presence of Fe3+ ions are highly specific, interference-free, can be monitored by smartphone and also observed within the live HeLa cells.

A turn-on fluorogenic chemosensor for Fe3+ and a Schottky barrier diode with frequency-switching device applications.

A novel highly sensitive and selective fluorescent chemosensor L has been synthesized and characterized by various physicochemical techniques. In 3 : 7 water : MeCN (v/v) at pH 7.2 (10 mM HEPES buffer, μ = 0.05 M LiCl), it selectively recognizes Fe3+ through 1 : 1 complexation resulting in a 106-fold fluorescence enhancement and a binding constant of 8.10 × 104 M-1. The otherwise non-fluorescent spirolactam form of the probe results a dual-channel (absorbance and fluorescence) recognition of Fe3+via CHEF (chelation enhanced fluorescence) through the opening of the spirolactam ring. We have also carried out fluorescence titration and anisotropy (r) studies in pure water in the presence of SDS (sodium dodecyl sulphate). Based on the dependence of FI (fluorescence intensity) and r on [SDS] it was proposed that the probe is trapped between two SDS monolayers which again interact among themselves by ππ stacking. As a result, there is an increase in FI up to [SDS] ∼ 7 mM - a phenomenon reminiscent of aggregation-induced enhancement of emission (AIEE). Beyond this concentration of SDS (7 mM), micelle formation takes place and the ππ stacked polymer now becomes a monomer and is trapped inside the micellar cavity. As a result, there is a decrease in FI at [SDS] > 7 mM. But for anisotropy, it increases with [SDS] beyond 7 mM. Ligand, metal, and SDS interactions are well established through different optical and morphological studies. [L-Fe(NO3)]2+ thin films on FTO (Fluorine-doped Tin Oxide) glass substrates have been designed with the help of the spin-coating deposition technique. The deposited film of thickness 1.6 × 10-5 cm is well characterized by optical band gap calculation with a direct band gap, εg ∼ 1.6 eV. FESEM was also performed for the [L-Fe(NO3)]2+/FTO film. The current-voltage characteristics were measured by the two-probe technique. Light-dependent exciton generation was carried out by taking the top and bottom contacts with graphite paste on FTO and on the [L-Fe(NO3)]2+ films for the measurement of switching behavior. The response ratio curve for the light-induced frequency-switching phenomena has been obtained. The frequency taped here is the oscillation frequency of the photo-generated electron and the hole in an exiton. Thus, the light-induced frequency-switching behavior and Schottky barrier diode characteristics of the material were established.

A thio-urea based chromogenic and fluorogenic chemosensor for expeditious detection of Cu2+, Hg2+ and Ag+ ions in aqueous medium

A novel simple reversible fluorescent and colorimetric multiple metal ions chemosensor L based on the thiourea has been designed, synthesized, and characterized by 1H NMR, IR spectroscopy, ESI–MS spectrometry and elemental analyses. The chemosensor L successfully detect Cu2+, Hg2+ and Ag+ based on binding site-signalling approach, where the thiourea group acts as binding site and the pyridine linked benzene ring acts as signalling unit. Distinct changes on UV–vis, fluorescence spectra and electrochemical behavior have been detected with the addition of Cu2+, Hg2+ and Ag+ ions along with the visual colour change in 1:1 methanol-water solution in the presence of other cations and anions (Fe3+, Co2+, Ni2+, Zn2+, Cd2+, Pb2+, Mn2+, Cr3+, F−, Br−, Cl−, AcO−, HSO4−, H2PO4− and CN−). The detection limits reach up to 10.67, 11.14 and 8.54 μM for Cu2+, Hg2+ and Ag+ ions respectively. L has been successfully applied for the determination of Cu2+, Hg2+ and Ag+ ions in real water samples. The minimum energy structure of L has been optimised by DFT calculations.

A new multi-analyte fluorogenic sensor for efficient detection of Al3+and Zn2+ions based on ESIPT and CHEF features

The synthesized ESIPT based fluorogenic chemosensor, H2L, selectively detects Zn2+and Al3+in a MeOH–H2O (4/1, v/v, pH = 7.2) medium.

Photo- and ionochromic indolyl(thienyl)maleimides containing naphthalimide linkers

Newly synthesized indolyl(thienyl)maleimides containing naphthalimide linkers were found to exhibit weak fluorescence due to PET effect. Irradiation at 436 nm wavelength led to the formation of their cyclic isomers. The obtained compounds showed the properties of chromogenic and fluorogenic chemosensors for F– ions.

Chromogenic and fluorogenic chemosensors for lethal cyanide ion. A comprehensive review of the year 2016

Among contrasting anions, CN− ion is extremely toxic and dangerous pollutant. Consequently, there is considerable interest in the colorimetric and fluorescent detection of CN− ions at trace level by using simple methods In this critical review begins with a brief discussion of the source, applications, toxicity of cyanide and mechanism of CN− ion sensor. Further, the fluorescent and colorimetric CN− ion sensors are classified according to their receptors into several categories like azine, azo, benzimidazole, benzothiazole, bisthiazole, BODIFY, coumarin, nanoparticles, hemicyanine, imine, indoline, malononitrile, naphthalene, naphthalimide, phenazine, pyrene, quinoline, rhodamine and thiazolidine functionalized sensing system in the year 2016.

Highly selective turn-on fluorogenic chemosensor for Zn(II) detection based on aggregation-induced emission

A simple and effective active aggregation-induced emission (AIE) fluorescent sensor, 1-(2-hydroxynaphthylmethylene)−2-(2-hydroxybenzylidene) hydrazine, was synthesized via a simple reaction requiring inexpensive reagents. It displayed swift response, excellent selectivity, and speedy sensitivity toward Zn2+ based on its notable chelation enhanced fluorescence/AIE characterization. The sensor can detect Zn2+ by colorimetric and selective turn-on fluorescence responses. Furthermore, the formation of the sensor–Zn2+ complex with 1:1 stoichiometry was confirmed by mass spectrometry. When the sensor bound with Zn2+, fluorescence-enhanced emission was observed via the chelation effect. Fluorescence intensity was considerably enhanced through aggregate formation when excessive Zn2+ was added. As the response time was ~5s, the sensor was used to track Zn2+ at real time. The sensor could detect Zn2+ as low as 46nM, and the recovery of urine samples with addition of Zn2+ ranged from 90.8% to 111.8%. The AIE mechanisms of the sensor and sensor–Zn2+ complex were explored by scanning electron microscopy, optical fluorescence microscope, and fluorescence reversibility study. In addition, the potential for practical applications was demonstrated through a simple and effective filter-paper-based method by exploiting the AIE mechanism.

A mechanistic study on unexpected and solvent-based pH-tuneable role of benzylic pendant side-arm on N2O2-donor naphthodiaza-crown macrocyclic ligand as a sensitive fluorogenic chemosensor for Al3+ in aqueous solution: X-ray, NMR, photophysical, and computational studies

Herein, we describe for the first time synthesis, characterization, chemosenor behavior, and mechanism of metal ion-ligand interaction of two novel side-armed naphthodiaza-crown macrocycles (L1 and L2) by employing of IR, 1H and 13C NMR, UV–vis, fluorescence spectroscopy, CHN microanalysis and single crystal X-ray diffraction. Preliminary fluorescence studies in ethanol as solvent revealed that the metal ion recognition by L1 was strongly different from L2 suggesting the importance of the number of benzylic side-arms on the extent of the interaction with Mn+. For instance employing fluorescence titration in ethanol showed binding constant values 105M−1 and 2.6×106M−1 for L1/Al3+ and L2/Al3+, respectively. Such metal ion selectivity by L2, however, was sharply improved in aqueous media (1:1v/v ethanol/water) in comparison with L1. The selective complex formation of L2 with Al3+ supported very low limit of detections, i.e. 5×10−7 and 7×10−6M in ethanol and aqueous medium, respectively. Single crystal X-ray diffraction analysis (in solid) as well as 1H NMR spectroscopy in acidic DMSO-d6 solvent revealed that unparalleled direction of the electron lone pairs on the donor atoms of L2 could not let Al3+ cation to be coordinated simultaneously by both nitrogen-donor groups on the macrocycle ring. The coordination of Al3+ with both of those nitrogen donors on L2, however, was evident from the 1H NMR spectra of L2/Al3+ where the solvent was DMSO-d6.