Intramolecular dual hydrogen bonded fluorescent "turn-on" probe for Al3+ and HSO4- ions: Applications in real water samples and molecular keypad lock

Dual hydrogen bonded Schiff base containing unsymmetrical double proton transfer sites, one with imine bond (CN) and hydroxyl group (OH), and the other with benzimidazole and hydroxyl groups has been successfully synthesized. Probe 1 displayed intramolecular charge transfer and acts as a potential sensor for Al³⁺ and HSO₄^- ions. Probe 1 displayed two absorption peaks at 325 nm and 340 nm and an emission band at 435 nm upon excitation at 340 nm. Probe 1 behaves as a fluorescence "turn-on" chemosensor for both Al³⁺ and HSO₄^- ions in H₂O-CH₃OH solvent system. The proposed method allows the determination of Al³⁺ and HSO₄^- ions up to 39 nM and 23 nM at emission wavelength 385 nm and 390 nm, respectively. The binding behavior of probe 1 towards these ions is determined by the Job's plot method and ¹H NMR titrations. Probe 1 is used to construct a molecular keypad lock where the absorbance channel can be opened only in the presence of the correct sequence. Further, it is used for the quantitative determination of HSO₄^- ion in different real-field water samples.

Bifunctional Cu2+/Fe3+ Probe with Independent Signal Outputs Based on a Photochromic Diarylethene with a Dansylhydrazine Unit

A novel dual-response fluorescent sensor based on a diarylethene photoswitching unit and a dansylhydrazine functional group has been synthesized. The compound exhibited high selectivity for Fe³⁺ and Cu²⁺ with independent fluorescence signal outputs. In the presence of Fe³⁺, the sensor formed a 1:1 metal complex, resulting in a remarkable "turn-off" fluorescence signal. On the other hand, its fluorescence intensity was notably enhanced (turn-on) and a color change from bright yellow to bright blue was observed when the sensor interacted with Cu²⁺, which was due to the hydrolysis reaction of the dansyl acid dye, as confirmed by high-resolution mass spectrometry-electrospray ionization and infrared spectrum. The detection limits were 9.73 × 10^-8 mol L^-1 for Fe³⁺ and 3.49 × 10^-7 mol L^-1 for Cu²⁺, respectively. From the unimolecular platform, two molecular logic circuits were constructed using the fluorescence emission intensity at 557/494 nm (Fe³⁺/Cu²⁺) as the outputs and the combined stimuli of Fe³⁺/ethylenediaminetetraacetic acid, Cu²⁺, and UV/vis as the inputs. In addition, the sensor was successfully used to determine Fe³⁺ in water samples from Ganjiang River and soil samples from Nanchang fields.

Fabrication of prime number checkers based on colorimetric responses of gold nanoparticles

In this work, we demonstrated the fabrication of molecular prime number checkers based on the concentration- and sequence-dependent colorimetric responses of citrate-capped gold nanoparticles (Au NPs) to two simple model chemicals, i.e. cysteine (Cys) and Hg²⁺ ions.

Polynuclear ampyrone based 3d coordination clusters

The use of a monoanionic Schiff base ligand in transition (Co, Ni and Cu) coordination chemistry yields mono-, tetra- and pentanuclear coordination clusters with different structural motifs.

Single sensor for multiple analytes in different optical channel: Applying for multi-ion response modulation

A Schiff-base, (2,4-di-tert-butyl-6-((2-hydroxyphenyl-imino)-methyl)phenol) (L), has been improved to function as a simultaneous multi-ion probe in different optical channel. The probe changes from colorless to orangish upon being deprotonated by F^-, while the presence of Al³⁺ significantly enhances the fluorescence of the probe due to the inhibition of CN isomerization, cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT), and chelation enhanced fluorescence (CHEF). Dual-channel "off-on" switching behavior resulted from the sequential input of F^- and Al³⁺, reflecting the balance of independent reactions of Al³⁺ and F^- with L and with one another. This sensing phenomenon realizes transformation between multiple states and beautifully mimics a "Write-Read-Erase-Read" logic circuit with two feedback loops.

Salicylyl Fluorene Derivatives as Fluorescent Sensors for Cu(II) Ions

Two derivatives of fluorene containing salicylic acid groups are successfully synthesized by palladium-catalyzed coupling reactions and subsequent hydrolysis of salicylate esters. The compounds are characterized by various spectroscopic methods. In phosphate buffer (pH 8.0) solutions, these compounds are well soluble. They show maximum absorption wavelengths in the range of 304-330 nm and exhibit maximum emission wavelength around 420 and 430 nm with the quantum yields of 2.7 and 4.4 %, respectively. The compound with alkynyl salicylate groups (2) exhibits a selective fluorescence quenching towards Cu(II) and Fe(II) with a relatively similar sensitivity. The selectivity favoring Cu(II) over Fe(II) and other metal ions can be achieved upon the addition of 30 μM Triton X-100. The Cu(II) detection limit in solution phase is 1.47 ppb. The fluorescence signal recovery upon the addition of EDTA indicate a reversible complexation between 2 and Cu(II) ion. Fabrication of 2 on filter paper using a 50 μM solution in THF affords a naked-eye detection for Cu(II) and Fe(II) in aqueous media at picomole level.

Selective chromo-fluorogenic molecular sensor for dual channel recognition of Cu2+and F−: effect of functional group on selectivity

The amido-Schiff base (3-hydroxy-naphthalene-2-carboxylic acid(4-cyano-benzylidene)-hydrazide) shows dual mode sensibility towards Cu²⁺and F⁻. It can detect Cu²⁺in HEK 293 cells and F⁻in tooth paste and in solid state.

A highly selective and reversible water-soluble polymer based-colorimetric chemosensor for rapid detection of Cu2+ in pure aqueous solution

A novel reversible colorimetric chemosensor based on polyethylene glycol has been developed to detect Cu²⁺ ions in pure aqueous solution.

Highly selective and sensitive colorimetric chemosensor for detection of Co2+ in a near-perfect aqueous solution

An outstanding colorimetric chemosensor was developed to selectively detect Co²⁺ with the lowest detection limit through the color change from colorless to yellow.

Dual mode selective chemosensor for copper and fluoride ions: a fluorometric, colorimetric and theoretical investigation

Sensor1can detect both copper and fluoride ions selectively in dual sensing mode. Moreover, it has been found to exhibit good membrane permeability for the detection of Cu²⁺in HEK 293 cells.

Dual-channel detection of Cu(2+) and F(-) with a simple Schiff-based colorimetric and fluorescent sensor

A simple and easily synthesized colorimetric and fluorescent receptor 1, based on 4-diethylaminosalicylaldehyde moieties as a binding and signaling unit, has been synthesized and characterized. The receptor 1 has a selective colorimetric sensing ability for copper (II) ion by changing color from colorless to yellow in aqueous solution, and could be utilized to monitor Cu(II) over a wide pH range of 4-11. In addition, the detection limit (12μM) of 1 for Cu(2+) is much lower than that (30μM) recommended by WHO in drinking water, and its copper complex could be reversible simply through treatment with a proper reagent such as EDTA. Moreover, receptor 1 exhibited both a color change from colorless to yellow and fluorescence enhancement with a red shift upon addition to F(-) in DMSO. The recognition mechanism was attributed to the intermolecular proton transfer between the hydroxyl group of the receptor and the fluoride.

Selective fluorescence sensing of salicylic acids using a simple pyrenesulfonamide receptor

The highest change in relative intensity of probe 3 among the probes 2–5 with 3,5-DNSA demonstrated the significance of sulfonamide N–H and imidazole C2–H with the highest association constant and complete quenching.

A novel reversible colorimetric chemosensor for the detection of Cu2+ based on a water-soluble polymer containing rhodamine receptor pendants

A novel reversible colorimetric chemosensor based on water-soluble polymer toward Cu²⁺ ions in pure aqueous solution has been developed.

A highly selective turn-on fluorescent sensor for fluoride and its application in imaging of living cells

A highly sensitive and selective fluorescent probe (FS) is based on a fluoride-specific desilylation reaction to yield a significant green fluorescence enhancement.