A new fluorogenic chemodosimetric system for mercury ion recognition

A new probe system for fluorogenic sensing of mercury ions has been designed and synthesized. It is the first intermolecular reaction-based fluorogenic chemodosimetric probe system for Hg(II) ion recognition. High and low concentrations of mercury ions gave different fluorescence responses that could easily be distinguished by the naked eye. This unique system allows detection of the concentration and presence of the mercury ion.     

Solvent-dependent chromogenic sensing for Cu and fluorogenic sensing for Zn and Al: a multifunctional chemosensor with dual-mode

A new multifunctional chemosensor 1 was synthesized and characterized by spectroscopic tools along with a single crystal X-ray crystallography. It can exhibit selective recognition responses toward Cu²⁺, Zn²⁺ and Al³⁺ in different solvent systems with bimodal methods (colorimetric and fluorescence). This sensor 1 detected Cu²⁺ ions through a distinct color change from colorless to yellow in aqueous solution. Interestingly, the receptor 1 was found to be reversible by EDTA. The detection limit (11 μM) of 1 for Cu²⁺ is much lower than WHO guideline (30 μM) in drinking water. In addition, the sensor 1 showed significant fluorescence enhancements in the presence of Zn²⁺ ion and Al³⁺ ion in two different organic solvents (DMF and MeCN), respectively. The binding modes of the three complexes were determined to be a 1:1 complexation stoichiometry through Job plot, ESI-mass spectrometry analysis, and ¹H NMR titration.     

Highly selective and sensitive fluorescence turn-on probe for a catalytic amount of Cu(I) ions in water through the click reaction

A simple azide-functionalized coumarin (1) was utilized as a fluorescence turn-on probe for a catalytic amount of Cu(I) ions in HEPES buffer. The probe has shown a selective and sensitive response to the cuprous ions over other various cations through a Cu(I)-mediated click reaction of 1 to an alkyne. When a catalytic amount of copper sulfates was added in the presence of ascorbate, the prominent fluorescence ‘Off-On’ change of 1 was observed so that submicromolar concentration of copper ions was detectable by the naked eye.     

Novel fluorescent chemosensor for Ag^ ＋ based on coumarin fluorophore

A novel chemosensor 1 （CS1） bearing one coumarin and two carbodithioate groups was synthesized and its fluorescent sensing behavior toward metal ions was investigated. Ag^＋ addition to a CH3COCH3/H2O （3：7, v：v） solution of CS1 gave a significantly quenched fluorescence. Other ions including Pb^2＋, Zn^2＋, Cu^2＋, Ca^2＋, Cd^2＋, Co^2＋, Mg^2＋, Mn^2＋, Hg^2＋, Ag^＋, Ni^2＋ induced no or much smaller spectral changes. This constitutes an ON-OFF Ag^＋-selective fluorescent chemosensor.     

Turn-on fluorescence sensor based on the aggregation of pyrazolo[3,4-b]pyridine-based coumarin chromophores induced by Hg

We developed a new fluorescent sensor (PPC-S) for Hg²⁺ based on the aggregation-induced emission (AIE) of pyrazolo[3,4-b]pyridine-based coumarin chromophore (PPC-O). Given the desulfurization reaction with Hg²⁺, AIE inactive PPC-S can be transformed into PPC-O with AIE activity, which can be employed for the fluorescence turn-on detection of Hg²⁺ with satisfactory selectivity and sensitivity in aqueous solutions.     

Synthesis of coumarin based fluorescent compounds

The reaction of different 7,8-disubstituted coumarin 4-acetic acids with 7-diethylaminocoumarin-3-carbaldehyde in the presence of piperidine in methanol gives highly fluorescent (E)-1-(7-diethylaminocoumarin-3-yl)-2-(7,8-disubstituted coumarin-4-yl)ethenes in good yield. Only the (E) diastereomers of these are obtained. The compounds are new, orange to red in colour and show emission in yellow to red region. These compounds were further studied for their emission properties.     

Fluorescence sensing of Cu and Hg by a dipyrene ligand involving an excimer-switch off mechanism

A novel dipyrene ligand 1 has been designed which shows intramolecular excimer formation in solution. Its specific interaction with Cu²⁺ or Hg²⁺ leads to the disruption of the excimer and results in a fluorescence-mediated sensing of these ions in a mixed organic-aqueous solution. Apart from steady-state studies, time-resolved fluorescence measurements also reveal that excimer-switch off caused by metal ion coordination leads to the selective detection of these ions.     

A rigid conjugated pyridinylthiazole derivative and its nanoparticles for divalent copper fluorescent sensing in aqueous media

A rigid conjugated pyridinylthiazole derivative (1) and two bithiazole derivatives with similar structures (2, 3) were synthesized and characterized. Their optical properties were investigated through spectral analysis. By applying the three compounds to Cu²⁺ ions detection, it was shown that compound 1 could be employed as a selective and sensitive Cu²⁺ ions fluorescent chemosensor. For aqueous assay, the nanoparticles of compound 1 were prepared in aqueous media. Compared to the monomer, 1 nanoparticles were more fluorescence sensitive to Cu²⁺ ions. Its binding mode with Cu²⁺ ions was correlated well with Langmuir equation. Compound 1 nanoparticles exhibit a dynamic working range for Cu²⁺ ions from 0.02 to 0.50 μM with a detection limit of 10 nM. The proposed chemosensor has been used for the direct measurement of Cu²⁺ content in drinking water samples with satisfying results.     

Fluorescent sensing platform for low-cost detection of Cu2+ by coumarin derivative: DFT calculation and practical application in herbal and black tea samples

A fluorogenic probe based on a coumarin-derivative for Cu²⁺ sensing in CH₃CN/H₂O media (v/v, 95/5, 5.0 μM) was developed and applied in real samples. 3-(4-chlorophenyl)-6,7-dihydroxy-coumarin (MCPC) probe was obtained by synthetic methodologies and identified by spectral techniques. The probe MCPC showed remarkable changes with a “turn-off” fluorogenic sensing approach for the monitoring of Cu²⁺ at 456 nm under an excitation wavelength of 366 nm. The response time of the probe MCPC was founded as only 1 min. The detection limit of the probe MCPC was recorded to be 1.47 nM. The binding constant and possible stoichiometric ratio (1:1) values were determined by Benesi-Hildebrand and Job’s plot systems, respectively. The mechanism of the probe MCPC with Cu²⁺ was further confirmed by ESI-MS and FT-IR analyses, as well as supported by theoretical calculations. Furthermore, the probe MCPC was successfully employed for the practical applications to sense Cu²⁺ in different herbal and black tea samples. The proposed sensing method was also verified by ICP-OES method.     

ICT-based Cu(II)-sensing 9,10-anthraquinonecalix[4]crown

A series of calix[4]arene-based chromogenic sensors bearing the 9,10-anthraquinone moiety have been synthesized and examined for their abilities to recognize various cations such as Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Cd²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Co²⁺, and Cu²⁺ by UV-vis spectroscopy. In acetonitrile, the presence of Cu²⁺ induces the formation of the 1:1 ligand/metal complex, which exhibits a new absorption band centered at 450 nm, and leads to an obvious color change from yellow to red.     

Magnesium optical one-shot sensor based on a coumarin chromoionophore

The characterization of a new irreversible optical absorption-based one-shot sensor for magnesium is described. The magnesium photoactive probe is 7-diethylamino-3-(3,4-ethylendioxybenzoyl)coumarin immobilized in a plasticized polymeric membrane. The magnesium selectivity can be explained in terms of size and charge density of magnesium and charge-separated resonance forms contribution in the excited state of coumarin. The selectivity obtained for magnesium over a variety of naturally occurring species in natural waters meets the requirements for the determination of this ion in water. The one-shot sensor responds between 0.14 and 14mgL(-1) with a sensor-to-sensor reproducibility of 1.3% as [Formula: see text] , at the medium level of the range. The performance of the optical one-shot sensor was tested in the analysis of magnesium in different types of natural waters and soft drinks validating results against a reference procedure.     

Synthesis and properties of novel calix[4]arene derivatives bearing fluorogenic coumarin units

Four novel calix[4]arene derivatives 5-8 bearing four fluorogenic coumarin units attached via imino group acting also as binding sites at the upper rim have been prepared and characterized by IR, IH NMR and MS. Compounds 5-8 adopt a cone conformation. Their complexation properties to different heavy and transition metal ions have been studied by UV-vis spectroscopy. Compounds 5, 6, 8 show selective recognition to Fe^3＋ and Cr^3＋.     

Synthesis and fluorescence properties of environment-sensitive 7-(diethylamino)coumarin derivatives

By linking 7-(diethylamino)coumarin and different aromatic groups via an oxazole moiety, a small series of new environment-sensitive fluorophores have been synthesized. They display varying degrees of environment-sensitivity, depending on the aromatic group present on the oxazole ring. Additionally, these coumarin-based fluorophores show considerably better photostability compared to the nitrobenzoxadiazole fluorophore, and offer a good starting point for the further development of these fluorophores into environment-sensitive membrane probes or for other applications requiring sensitivity to the environment.     

A coumarin based ICT probe for fluoride in aqueous medium with its real application

A new coumarin based hydrazone (receptor 1) synthesized by modifying one of our earlier reported receptor detected fluoride ion selectively through naked eye in aq. DMSO (5:95, v/v). It was also able to detect fluoride through naked eye in a toothpaste sample. The addition of 1 equiv. of fluoride as its tetrabutylammonium salt to the 5 × 10⁻⁵ M aq. DMSO solution of the receptor 1 produced red color while the similar addition of acetate produced faint pink color. The dihydrogenphosphate and a variety of other anions were not able to produce any significant color change with receptor 1 under similar experimental conditions. The corresponding UV-vis measurements showed a bathochromic shifting of 455 nm band of receptor 1 to 514 and 484 nm for fluoride and acetate, respectively. The non-linear fittings of corresponding UV-vis titration data in 1:1 binding equation yielded association constants in 10⁵:1 ratio for fluoride and acetate, respectively. The ¹H NMR titrations studies shade further light on their mode of binding with receptor 1. The quantum mechanical calculations through time dependant density functional theory (TD-DFT) using basis set b3lyp/6-311g** supported our experimental findings nicely.     

A ratiometric fluorescent chemodosimeter for Cu(II) in water with high selectivity and sensitivity

Coumarin derivative 1 was synthesized as an efficient ratiometric chemodosimeter for the detection of Cu(II) in 99% water/DMSO (v/v) at pH 7.0. Mechanism studies suggested that 1 formed a complex with Cu(II) at 2:1 ratio accompanied by quenching of green fluorescence at 524 nm; when the solution was heated to 50 °C for 30 min, Cu(II)-promoted hydrolysis of coumarin lactone moiety of 1 occurred with bright blue fluorescence at 451 nm emerged. With fluorescence intensity ratio detection at 451 nm and 524 nm, 1 features an excellent sensitivity with the detection limit of 15 nmol L⁻¹ toward Cu(II) and a good selectivity over other metal ions.     

A dimeric copper coumarin complex: synthesis and crystal structure of [{Cu(4-methyl-7-(salicylideneamino)coumarin)2}2]

A binuclear copper complex [{Cu(L)₂}₂], C₆₈H₄₈Cu₂N₄O₁₂C (where L is 4-methyl-7-(salicylideneamino)coumarin), has been synthesized and characterized using elemental analysis, molar conductance measurements, and infrared, ultraviolet and ESR spectrosopy. The molecular structure of title compound, determined by single-crystal X-ray diffraction studies, reveals that the two symmetric Cu(L)2 units are associated into a dimer by rather long Cu...O bonds. The Cu(II) ions are bridged via the phenolic oxygen of one of the monomers and have distorted trigonal bipyramidal conformation geometry. Within each monomer the two methylsubstituted coumarin skeletons are trans to one another, but adopt a parallel arrangement with respect to the other monomer. Only half of the complex molecule can be found in the asymmetric unit, Z′ = 0.5, the other half is generated by the symmetry centre.      

A vic -dioxime ligand bearing fluorescent coumarin moieties and its complexes; preparation,spectroscopy, and electrochemistry

The synthesis of a new vic-dioxime ligand, N,N′²-dihydroxy-O ¹,O ²-bis(4-methyl-2-oxo-2H-chromen-7-yl)oxalimidamid (LH₂) (1), bearing functional coumarins and its soluble mono- {Ni(II), Cu(II), Co(II)} and dinuclear {UO₂(II)} complexes are presented. The fluorescence properties due to the 7-hydroxy-4-methylcoumarin fluorophore, which is conjugated with vic-dioxime that functions as the MN₄ core of 1 and its complexes, are also reported. The formation of coordination complexes resulted in the blue shift in excitation spectrum and fluorescence quenching of 1. Both mononuclear {(LH)₂M, M=Ni(II), Cu(II), and Co(II)} and homodinuclear {(LH)₂(UO₂)₂(OH)₂)} complexes have been obtained with metal?:?ligand ratios of 1?:?2 and 2?:?2, respectively. The characterizations of the new compounds were made by elemental analysis, ¹H-NMR, FT-IR, UV-Vis, and LCMS data. Redox behavior of 1, involving oxime and coumarin moieties, and its complexes with Ni(II), Cu(II), Co(II) and UO₂(II) were investigated by cyclic voltammetry. The comparison of the electrochemical behavior of 1 with its complexes enabled us to identify metal-, oxime- and coumarin-based signals.     

Synthesis and characterization of novel α- or β-tetra[6,7-dihexyloxy-3-(4-oxyphenyl)coumarin]-substituted metal-free and metallo phthalocyanines

The synthesis of novel phthalonitriles substituted at 3- or 4-position with 6,7-dihexyloxy-3-(4-oxyphenyl)coumarin were performed. The metal-free and metallo phthalocyanines (MPcs) (M = Zn, Co, Cu) were prepared by cyclotetramerization of 6,7-dihexyloxy-3-[p-(2′,3′-dicyanophenoxy)phenyl]coumarin or 6,7-dihexyloxy-3-[p-(3′,4′-dicyanophenoxy)phenyl]coumarin. The newly prepared compounds, phthalonitriles and Pcs, have been characterized by elemental analysis, ¹H NMR, ¹³C NMR, MALDI-TOF, IR, UV–Vis and fluorescence spectral data. The electronic spectra exhibit bands of coumarin identity along with characteristic Q and B bands of the Pc core. The IR-spectra of all Pcs showed three characteristic intense bands at 1709–1700 cm⁻¹ for lactone carbonyl, two bands at 1489–1604 cm⁻¹ for conjugated olefinic system.     

Design and synthesis of a new coumarin-based ‘turn-on’ fluorescent probe selective for Cu

The novel coumarin-based ‘turn-on’ fluorescent probe (E)-3-(2,5-dimethoxybenzylideneamino)-7-hydroxy-2H-chromen-2-one (MGM) was designed, synthesized, and characterized. This compound shows high selectivity for Cu⁺², combined with a large fluorescence enhancement upon binding to Cu²⁺. Benesi-Hildebrand and Job plots demonstrate that the stoichiometry of the Cu²⁺ complex formed is 2:1. Preliminary studies employing epifluorescence microscopy demonstrated that Cu⁺² could be imaged in human neuroblastoma SH-SY5Y cells treated with MGM.     

A TPA-caged precursor of (imino)coumarin for “turn-on” fluorogenic detection of Cu

We strategize to utilize the precursors of (imino)coumarin fluorophores to deliver novel reactive Cu⁺ probes, where tris[(2-pyridyl)-methyl] amine (TPA) works as a reactive receptor towards Cu⁺. To verify this strategy, CP1, a representative probe and relevant sensing behaviors towards Cu⁺ are presented here. CP1 features good solubility and fast response for monitoring labile copper in aqueous solution and live cells. The sensing mechanism of CP1 is determined by HPLC titration and mass spectrometric analysis. The probe CP1 exhibits a 60-fold fluorescence enhancement and a detection limitation of 10.8 nM upon the detection of Cu⁺. CP1 is further applied for imaging labile copper in live cells. This work provides a starting point for future development of Cu⁺ probes, based on in situ formation of (imino)coumarin scaffolds, as well as their further investigations of copper signaling and biological events.