Coumarin Based Fluorescent Probe for Colorimetric Detection of Fe<Superscript>3+</Superscript> and Fluorescence Turn On-Off Response of Zn<Superscript>2+</Superscript> and Cu<Superscript>2+</Superscript>

A new coumarin based Schiff-base chemosensor-(E)-7-(((8-hydroxyquinolin-2-yl)methylene) amino)-4-methyl-2H-chromen-2-one (H ₁₁ L) was synthesized and evaluated as a colorimetric sensor for Fe³⁺ and fluorescence “turn on-off” response of Zn²⁺ and Cu²⁺ using absorption and fluorescence spectroscopy. Upon treatment with Fe³⁺ and Zn²⁺, the absorption intensity as well as the fluorescence emission intensity increases drastically compared to other common alkali, alkaline earth and transition metal ions, with a distinct color change which provide naked eye detection. Formation of 1:1 metal to ligand complex has been evaluated using Benesi-Hildebrand relation, Job’s plot analyses, ¹H NMR titration as well as ESI-Mass spectral analysis. The complex solution of H ₁₁ L with Zn²⁺ ion exhibited reversibility with EDTA and regenerate free ligand for further Zn²⁺ sensing. H ₁₁ L exhibits two INHIBIT logic gates with two different chemical inputs (i) Zn²⁺ (IN1) and Cu²⁺ (IN2) and (ii) Zn²⁺ (IN1) and EDTA (IN2) and the emission as output. Again, an IMPLICATION logic gate is obtained with Cu²⁺ and EDTA as chemical inputs and emission as output mode. Both free ligand as well as metal-complexes was optimized using density functional theory to interpret spectral properties. The corresponding energy difference between HOMO-LUMO energy gap for H ₁₁ L, H₁₁L-Zn²⁺ and H₁₁L-Cu²⁺ are 2.193, 1.834 and 0.172 eV, respectively.     

A highly Selective Fluorescent Sensor for Monitoring Cu<Superscript>2+</Superscript> Ion: Synthesis,Characterization and Photophysical Properties

A new fluorescent sensor, 4-allylamine-N-(N-salicylidene)-1,8-naphthalimide (1), anchoring a naphthalimide moiety as fluorophore and a Schiff base group as receptor, was synthesized and characterized. The photophysical properties of sensor 1 were conducted in organic solvents of different polarities. Our study revealed that, depending on the solvent polarity, the fluorescence quantum yields varied from 0.59 to 0.89. The fluorescent activity of the sensor was monitored and the sensor was consequently applied for the detection of Cu²⁺ with high selectivity over various metal ions by fluorescence quenching in Tris-HCl (pH = 7.2) buffer/DMF (1:1, v/v) solution. From the binding stoichiometry, it was indicated that a 1:1 complex was formed between Cu²⁺ and the sensor 1. The fluorescence intensity was linear with Cu²⁺ in the concentration range 0.5–5 μM. Moreso, the detection limit was calculated to be 0.32 μM, which is sufficiently low for good sensitivity of Cu²⁺ ion. The binding mode was due to the intramolecular charge transfer (ICT) and the coordination of Cu²⁺ with C = N and hydroxyl oxygen groups of the sensor 1. The sensor proved effective for Cu²⁺ monitoring in real water samples with recovery rates of 95–112.6 % obtained.     

A Dual-Target Fluorescent Probe with Response-Time Dependent Selectivity for Cd<Superscript>2+</Superscript> and Cu<Superscript>2+</Superscript>

A novel fluorescent probe (NT) was developed by merging 2-hydrazinylbenzothiazole with 2-hydroxy-1-naphthaldehyde for the detection of Cd²⁺ and Cu²⁺. The probe alone is almost nonfluorescent due to the isomerization of C=N in the excited state. The addition of Cd²⁺ can cause an immediate strong green fluorescence owing to the suppression of C=N isomerization by Cd²⁺-coordination. Furthermore, NT gives a delayed turn-on fluorescence response to Cu²⁺ although it is a vigorous fluorescence quencher, which was thanks to the inhibition of the electron transfer between excited fluorophore and paramagnetic Cu²⁺ by sulfur donor. Based on fluorescence spectra and ESI-MS analysis, the binding modes between NT and Cd²⁺/Cu²⁺ were proposed.     

A Turn-on Fluorescent Chemosensor for Zn<Superscript>2+</Superscript> Based on Quinoline in Aqueous Media

A simple “off-on fluorescence type” chemosensor 1 3-((2-(dimethylamino)ethyl)amino)-N-(quinolin-8-yl)propanamide has been synthesized for Zn²⁺. The receptor 1 comprises the quinoline moiety as fluorophore and the N,N^′-dimethylethane-1,2-diamine as a binding site. 1 showed a remarkable fluorescence enhancement in the presence of Zn²⁺ in aqueous solution. Importantly, the chemosensor 1 could be used to detect and quantify Zn²⁺ in water samples. In particular, this chemosensor could clearly distinguish Zn²⁺ from Cd²⁺. The binding properties of 1 with Zn²⁺ ions were investigated by UV-vis, fluorescence, electrospray ionization mass spectroscopy and ¹H NMR titration.     

A Ratiometric and near-Infrared Fluorescent Probe for Imaging Cu<Superscript>2+</Superscript> in Living Cells and Animals

We have rationally constructed a novel ratiometric and near-infrared Cu²⁺ fluorescent probe based on a tricarbocyanine chromophore. The new probe NIR-Cu showed a ratiometric fluorescent response to Cu²⁺ with a large emission wavelength shift (up to 142 nm) in the far-red to near-infrared region. The probe also displayed a large variation in the fluorescence ratio (I₆₃₆/I₇₇₈) to Cu²⁺ species with high sensitivity and selectivity. Additionally, the developed probe NIR-Cu was suitable for fluorescence imaging of Cu²⁺ in living cells and mice.     

Luminescent Benzothiazole-Based Fluorophore of Anisidine Scaffoldings: a “Turn-On” Fluorescent Probe for Al<Superscript>3+</Superscript> and Hg<Superscript>2+</Superscript> Ions

A new anisidine possessing benzothiaozle-based chemosensor (1) has been designed and synthesized. The chemosensor 1 was designed to provide hard base environment for ratiometric detection of comparatively less studied Al³⁺ ions. In CH₃CN, the fluorescence spectra of chemosensor 1 red shifted from 368 to 430 nm with addition of Al³⁺ and Hg²⁺ ions; while Cu²⁺ ions caused quenching of emission intensity of 1. These differential changes observed with Al³⁺ and Cu²⁺ ions addition enabled chemosensor 1 to construct “NOR” and “TRANSFER” logic gates.     

A Highly Selective and Sensitive Fluorescent Chemosensor for Aluminum Ions Based on Schiff Base

An efficient “off–on” type fluorescent chemosensor, (E)-N′-(4-(diethylamino)-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H ₂ L), based on Schiff base for the determination of Al³⁺ has been designed, synthesized, and evaluated. Upon treated with Al³⁺, the fluorescence of H ₂ L was enhanced 45-fold due to the chelation-enhanced fluorescence (CHEF) effect based on the formation of a 1:1 complex between the chemosensor and Al³⁺. Other metal ions, such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Cu²⁺, Ga³⁺, Zn²⁺, Cr³⁺, Cd²⁺, Ag⁺, Fe³⁺, In³⁺, Mn²⁺, Pb²⁺, Co²⁺, and Ni²⁺ had little effect on the fluorescence. The results demonstrate that the chemosensor H ₂ L has stronger affinity with Al³⁺ than other metal ions. The detection limit of H ₂ L for sensing Al³⁺ is 3.60 × 10^?6 M in EtOH–H₂O (3:7, v/v) solution. And the recognizing behavior has been investigated both experimentally and computationally.     

Rhodamine Based Turn-On Sensors for Ni<Superscript>2+</Superscript> and Cr<Superscript>3+</Superscript> in Organic Media: Detecting CN<Superscript>−</Superscript> via the Metal Displacement Approach

Two novel sensors bearing rhodamine B and quinoline units have been synthesized. One of these, 1, allows sensitive and selective detection of Ni²⁺ and Cr³⁺ by forming non-fluorescent (1-Ni²⁺) and fluorescent (1-Cr³⁺) complexes respectively. Both metals trigger the formation of highly colored ring-open spirolactam. These form excellent probes for CN^? which quenches the fluorescence of the 1-Cr³⁺ complex by extracting the Cr³⁺. Both Cr³⁺ and Cu²⁺ gave color changes with 2, but they are easily identified separately via the large fluorescence enhancement that occurs only with Cr³⁺.     

A Dansyl-Rhodamine Ratiometric Fluorescent Probe for Hg<Superscript>2+</Superscript> Based on FRET Mechanism

Based on resonance energy transfer (FRET) from dansyl to rhodamine 101, a new fluorescent probe (compound 1) containing rhodamine 101 and a dansyl unit was synthesized for detecting Hg²⁺ through ratiometric sensing in DMSO aqueous solutions. This probe shows a fast, reversible and selective response toward Hg²⁺ in a wide pH range. Hg²⁺ induced ring-opening reactions of the spirolactam rhodamine moiety of 1, leading to the formation of fluorescent derivatives that can serve as the FRET acceptors. Very large stokes shift (220 nm) was observed in this case. About 97-fold increase in fluorescence intensity ratio was observed upon its binding with Hg²⁺.     

Enhanced photocatalytic activity of ternary CuInS<Subscript>2</Subscript> nanocrystals synthesized from the combination of a binary Cu(I)S precursor and InCl<Subscript>3</Subscript>

Ternary copper indium sulfide (CIS) nanocrystals (NCs) have been synthesized by mixing of binary precursor [Cu^I(bdpa)₂][Cu^ICl₂] (1) and/or [Cu^I(mdpa)₂][Cu^ICl₂] (2) (where, mdpa and bdpa represent methyl and benzyl ester of 3,5-dimethyl pyrazole-1-dithioic acid, respectively) with InCl₃ in a low-temperature solvothermal process. The +1 oxidation state of copper and the atomic ratio Cu to S (1:2) is atomically maintained in the pyrazole-based Cu(I)–S precursor to synthesize phase pure CuInS₂. Coordinating solvents like ethylene diamine (EN) and ethylene glycol (EG) have been used in the synthesis without any surfactants. No use of external surfactants in the synthesis of CIS nanoparticles reveals that precursor acts as stabilizing agent. The synthesized nanocrystals were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDX) studies. The optical property of the nanocrystals shows a pronounced quantum confinement effect in the particles with band gap energy ca. 1.5 eV. The formation mechanism of ternary CIS has been proposed. The pore size distributions of the particles show the average pore diameters 13.1 nm from 1 and 5.3 nm from 2. The calculated values of the specific surface area are 8.123 and 9.577 m²/g for 1 and 2, respectively. The excellent photocatalytic degradation of rose bengal (RB) and rhodamine B (RhB) was demonstrated by the porous CIS nanocrystals.

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Graphical abstract Enhanced photocatalytic activity of ternary CuInS₂ nanocrystals synthesized from the combination of a binary Cu(I)S precursor and InCl₃. Gopinath Mondal, Ananyakumari Santra, Sumanta Jana, Nimai Chand Pramanik, Anup Mondal and Pulakesh Bera

     

A New Piperidine Derivatized-Schiff Base Based “Turn-on” Cu<Superscript>2+</Superscript>Chemo-Sensor

In this study, we report the synthesis of new Schiff base E-1-(((1-benzylpiperidin-4-yl)imino)methyl)naphthalenee-2-ol (L) and evaluation of its fluorescence response toward Cu²⁺ ion. Preliminary, solvent effect, metal selectivity and metal ligand ratio were analyzed through UV-Visible study. Fluorescence response toward Cu²⁺ was carried to assess the fluorescent property of synthesized Schiff base. The probe exhibited a higher fluorescence enhancement in the presence of Cu²⁺ over other metal ions (Ni²⁺, Zn²⁺, Hg²⁺, Co²⁺, Cd²⁺, Al³⁺, Fe²⁺, and Pb²⁺). The binding stoichiometry between L and Cu²⁺ has been investigated using Job’s plot and Benesi-Hildebrand equation and it was found that ligand L can form 1:1 L-Cu²⁺ complex with binding constant (K _a) of 4?×?10⁴ LM^?1.     

Hexa-BODIPY Linked-Triazole Based on a Cyclotriphosphazene Core as a Highly Selective and Sensitive Fluorescent Sensor for Fe<Superscript>2+</Superscript> Ions

A new type of fluorescent chemosensor based on tethered hexa-borondipyrromethene cyclotriphosphazene platform (HBTC) linked via triazole groups was designed and synthesized. Its sensing behavior toward metal ions was investigated by ultraviolet-visible and fluorescence spectroscopies. Addition of a Fe²⁺ ion to a tetrahydrofuran solution of HBTC gave a visual color change as well as a significantly quenched fluorescence emission, while other tested 19 metal ions induced no color or spectral changes. This compound was found to be highly selective and sensitive for Fe²⁺ with a low limit of detection (2.03 μM) which is, to the best of our knowledge, the superior than the previously studied chemosensors for Fe²⁺.

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Graphical Abstract ?

     

Linear theory of random textures of <Superscript>3</Superscript>He-A in an aerogel

The spatial variation of the orbital part of the order parameter of ³He-A in an aerogel has been represented as random walk of a unit vector l(r) over a sphere under the action of random anisotropy created by the system of strands of the aerogel. The statistical properties of the resulting random texture have been studied. For distances at which the variation of l is much smaller than its magnitude, the average square <δl²> of variation of l has been expressed in terms of the correlation function of the component of the random anisotropy tensor. Under simplifying assumptions on the structure of this correlation function, an analytical dependence of <δl²> on r has been obtained for isotropic and axially anisotropic aerogels. The average values of the squares of the projections of l on the axes of anisotropy for an anisotropic aerogel have been represented in terms of the parameters of the aerogel. The characteristic scale at which the long-range order is broken, as well as the magnitude of global anisotropy sufficient for the recovery of the long-range order, has been numerically estimated within a simple model. The values obtained have been compared to other estimates.     

A Fluoro-Chromogenic Sensor Based on Organic Molecular Framework for Cu<Superscript>2+</Superscript> and F<Superscript>−</Superscript> in Aqueous Soluble DMSO

The 2,2′-dinaphtholazobenzene molecular framework (P) was designed, synthesized and characterized. Its absorption and fluorescence properties revealed that P is a dual sensor for copper ions (Cu²⁺) and fluoride ions (F^?) in DMSO. The colorimetric activities were clearly visible by naked eye upon the addition of the two ions. Fluorescence quenching and enhancement were observed when Cu²⁺ and F^? ions were added respectively. Density Functional Theory (DFT) calculations were carried out to provide an insight into the interaction of guest ions (Cu²⁺ and F^?) with P, and to explain how the molecular orbitals were affected.

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Graphical Abstract ?

     

Coumarin Based Highly Selective “off-on-off” Type Novel Fluorescent Sensor for Cu<Superscript>2+</Superscript> and S<Superscript>2−</Superscript> in Aqueous Solution

Solvent free synthesis of 6,7-dihydroxy-3-(3-chlorophenyl) coumarin (CFHC) was designed and obtained by the interaction of 2-(2,4,5-trimethoxyphenyl)-1-(3-chlorophenyl)acrylonitrile with pyridinium hydrochloride in the presence of silica gel by using microwave irradiation. The characterization of CFHC was confirmed by FT-IR, ¹H, ¹³C, ¹³C–APT and 2D HETCOR spectroscopy methods. The optical behavior of CFHC towards metal ions was investigated by UV-visible and fluorescence spectroscopy. CFHC showed “on–off” type fluorescence response towards Cu²⁺ with high selectivity in aqueous solution (CH₃CN/H₂O, 9/1, v/v). Once binding with Cu²⁺, CFHC-Cu²⁺ complex also displayed high selectivity for sulfide, resulting in “off–on” type sensing of sulfide anion.

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Graphical abstract Visual fluorescence changes upon addition of various metal ions (5.0 eq.) to CFHC in CH₃CN/H₂O (90:10, v/v) under UV excitation (365 nm)

     

Paramagnetic resonance and off-center location of Cu<Superscript>2+</Superscript> ions in ferroelectric lead germanate

This paper reports on the results of investigations into the orientation behavior of the splitting of the electron paramagnetic resonance spectrum due to the location of paramagnetic ions in different domains of Cu²⁺-containing lead germanate. The off-diagonal components of the tensor g for Cu²⁺ quasi-monoclinic centers are determined. A model for off-central displacement of copper ions is proposed with due regard for the revealed symmetry of paramagnetic centers, their superhyperfine structure, and the orientation of the magnetic axes.     

A New Fluorescent “Turn-Off” Coumarin-Based Chemosensor: Synthesis,Structure and Cu-Selective Fluorescent Sensing in Water Samples

We report the synthesis and characterization two coumarin-based fluorescence probes, N′-{[7-(diethylamino)-2-oxo-2H-chromen-3-yl]carbonyl}pyridine-3-carbohydrazide (3) and N′-benzoyl-7-(diethylamino)-2-oxo-2H-chromene-3-carbohydrazide (4), proposed as a novel fluorescent chemosensor. The two probes designed showed an instant turn-off fluorescence response to Cu²⁺ over other metal ions in ethanol-water mixture based on intramolecular charge transfer (ICT). It was found that pyridine-analogue coumarin is highly selective and sensitive sensor for Cu²⁺. The 3 sensor coordinates Cu²⁺ in 1:1 stoichiometry with a binding constant, K_a = 5.22 M^?1 and the detection limit was calculated 1.97 × 10^?9 M.     

A Fluorescent Hypochlorite Probe Built on 1,10-Phenanthroline Scaffold and its Ion Recognition Features

In this study, the synthesis of 7-((Hydroxyimino)methyl)-1,10-phenanthroline-4-carbaldehyde oxime (1) in two steps starting from 4,7-dimethyl-1,10-phenanthroline (2) is reported. It is found that compound 1 can be used as a fluorogenic probe for the detection of hypochlorite ion in aqueous solution. NMR and mass spectral analysis indicate that probe 1 undergoes a chemical transformation through its oxime units upon treatment with hypochlorite, which results in a remarkable enhancement of the emission intensity. Also, metal ion recognition properties of probe 1 is investigated. It is noted that compound 1 is responsive to Zn²⁺, Cd²⁺, Ni²⁺ and Cu²⁺ metal ions, which reduced the emission intensity under identical conditions.

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Graphical Abstract The design, synthesis and properties of a new fluorescent hypochlorite probe is described. It is found that probe 1 immediately undergoes an oxidation reaction with NaClO through its oxime units in 0.1 M Na₂CO₃-NaHCO₃ buffer containing DMF (pH = 9.0, 30:1 v/v) at room temperature, which resulted in a remarkable enhancement of the emission intensity. It is noteworthy that this novel probe 1 is highly selective to hypochlorite ion when compared to some other ROS and anions. On the other hand, probe 1 also induces turn-off fluorogenic responses to metal ions such as Zn²⁺, Cd²⁺, Ni²⁺ and Cu²⁺ ions under identical conditions.

     

Influence of the ground state of the Pr<Superscript>3+</Superscript> ion on magnetic and magnetoelectric properties of the PrFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> multiferroic

The magnetic, magnetoelectric, and magnetoelastic properties of a PrFe₃(BO₃)₄ single crystal and the phase transitions induced in this crystal by the magnetic field are studied both experimentally and theoretically. Unlike the previously investigated ferroborates, this material is characterized by a singlet ground state of the rare-earth ion. It is found that, below T _N = 32 K, the magnetic structure of the crystal in the absence of the magnetic field is uniaxial (l ∥ c), while, in a strong magnetic field H ∥ c (H _cr ～ 43 kOe at T = 4.2 K), a Fe³⁺ spin reorientation to the basal plane takes place. The reorientation is accompanied by anomalies in magnetization, magnetostriction, and electric polarization. The threshold field values determined in the temperature interval 2–32 K are used to plot an H-T phase diagram. The contribution of the Pr³⁺ ion ground state to the parameters under study is revealed, and the influence of the praseodymium ion on the magnetic and magnetoelectric properties of praseodymium ferroborate is analyzed.     

Electron paramagnetic resonance of Cr<Superscript>3+</Superscript>-Li<Superscript>+</Superscript> centers in (Cr,Li): Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript> synthetic forsterite

Synthetic single crystals of chromium-and lithium-doped forsterite, namely, (Cr,Li): Mg₂SiO₄, are studied using electron paramagnetic resonance spectroscopy. It is revealed that, apart from the known centers Cr³⁺(M1) and Cr³⁺(M2) (with local symmetries C_i and C_s, respectively), these crystals involve two new types of centers with C₁ symmetry, namely, Cr³⁺(M1)′ and Cr³⁺(M2)′ centers. The standard parameters D and E in a zero magnetic field [zero-field splitting (ZFS) parameters expressed in GHz] and principal components of the g tensor are determined as follows: D=31.35, E=8.28, and g=(1.9797, 1.9801, 1.9759) for Cr³⁺(M1)′ centers and D=15.171, E=2.283, and g=(1.9747, 1.9769, 1.9710) for Cr³⁺(M2)′ centers. It is found that the lowsymmetric effect of misalignment of the principal axes of the ZFS and g tensors most clearly manifests itself (i.e., its magnitude reaches 19°) in the case of Cr³⁺(M2)′ centers. The structural models Cr³⁺(M1)-Li⁺(M2) and Cr³⁺(M2)-Li⁺(M1) are proposed for the Cr³⁺(M1)′ and Cr³⁺(M2)′ centers, respectively. The concentrations of both centers are determined. It is demonstrated that, upon the formation of Cr³⁺-Li⁺ ion pairs, the M1 position for chromium appears to be two times more preferable than the M2 position. Reasoning from the results obtained, the R₁ line (the ²E → ⁴A₂ transition) observed in the luminescence spectra of (Cr,Li): Mg₂SiO₄ crystals in the vicinity of 699.6 nm is assigned to the Cr³⁺(M1)′ center.