Synthesis of naphthalene-fused imidazo[1,2-a]pyridinium salts showing green luminescence with high quantum yields and large Stokes shift

We have synthesized naphthalene-fused imidazo[1,2-a]pyridines by a novel electrophilic iodocyclization of 2-alkynyl-3-arylimidazo[1,2-a]pyridines. Notably, their quaternized salts exhibited green emission with unexpectedly high quantum yields and mega-large Stokes shift and were successfully used for mitochondrial imaging.

A fluorescent chemosensor for selective detection of chromium (III) ions in environmentally and biologically relevant samples

A simple single step one pot multicomponent reaction was performed to synthesize N-(tert-butyl)-2-(furan-2-yl)imidazo[1,2-a]pyridine-3-amine (TBFIPA). The synthesized TBFIPA was subjected to library of cations to study its ability for selective and sensitive detection of specific metal ions. Selective detection of chromium ions by TBFIPA were found from the significant hypsochromic shift (335 nm → 285 nm) in the UV-Visible spectra. The fluorescent TBFIPA displays complete quenching of fluorescence under UV lamp (365 nm) only in the presence of chromium without the interference of common metal ions. Binding constant (ka) obtained from Benesi-Hildebrand plot is 0.21 × 105 M-1, limit of detection (LOD) and limit of quantification (LOQ) of TBFIPA toward Cr3+ ions are 4.70 × 10-7 M and 1.56 × 10-7 M, respectively. The mechanism proposed during complex formation were supported by stoichiometric Job continuous variation plot, 1H NMR titration and ESI-MS spectroscopic data. All the experimental confirmation for complex formation were corroborated with theoretical DFT studies optimized using RB3LYP/6-31G(d) basis set. The selectivity and sensitivity of TBFIPA toward Cr3+ ions are found suitable to design a user-friendly silica based portable test kit. Alongside, TBFIPA was successfully utilized for imaging onion epidermal cells. Furthermore, the results obtained for biological, environmental, and industrial samples provided solid evidence to estimate chromium ions using TBFIPA in these real samples.

A Review on Thiazole Based Colorimetric and Fluorimetric Chemosensors for the Detection of Heavy Metal Ions

Thiazole and its derivatives play an important role in biological and non-biological fields due to several structural and electronic behaviors associated with it. Thiazole derivatives act as chemosensors because they formed metal complexes upon interacting with various heavy metal ions like Cd2+, Co2+, Cr3+, Fe3+, Ag+, Al3+, Cu2+, Pd2+, Hg2+, Ni2+, Ga3+, In3+, Sn4+, Pb2+, Zn2+ as well as other cations. These metal ions are of prime importance from the environmental point of view with high. This review article focuses on the thiazole-based colorimetric as well as fluorometric sensor for the recognition of different heavy metal cations in various specimens like agricultural, biological, and environmental. It also summarizes the binding stoichiometry, detection limit, pH, structure, and practical application of the reported thiazole-based chemosensors. Further, the sensing performances, have been discussed and compared with some reported organic sensors.

Medicinal importance and chemosensing applications of Schiff base derivatives for the detection of metal ions: A review

Schiff bases, named after Hugo Schiff, are formed when primary amine reacts with carbonyl compounds (aldehyde or ketone) under specific conditions. Schiff bases are economical, simple synthetic routes, and easily accessible in laboratories. They have medicinal and biological applications such as antiviral, antioxidant, antifungal, anticancer, anthelmintic, antibacterial, antimalarial, anti-inflammatory, antiglycation, anti-ulcerogenic, and analgesic potentials. A number of Schiff bases are reported for the detection of various metal ions. They are also used as catalysts, polymer stabilizers, intermediates in organic synthesis, and corrosion inhibitors. In this review, we have highlighted the recent advancements in the development of bioactive Schiff base derivatives and their sensing applications for detecting metal cations. Additionally, various spectroscopic techniques for structural characterization, such as X-ray diffraction analysis (XRD), FT-IR, UV-vis, and NMR spectroscopy were also discussed.

Application of 2,4,5-Tris(2-pyridyl)imidazole as "Turn-Off" Fluorescence Sensor for Cu (II) and Hg (II) ions and in vitro Cell Imaging

The 2,4,5-tris(2-pyridyl)imidazole (L) molecule has been evaluated as a probe for dual sensing of Hg²⁺ and Cu²⁺ ions in EtOH/HEPES buffer medium (5mM, pH=7.34, 1:1, v/v). Probe L shows a good sensitive and selective turn-off response in the presence of both Hg²⁺ and Cu²⁺ ions, which is comprehensible under long UV light. The probe can detect Cu²⁺ ion in the pH range of 3-11 and Hg²⁺ ion in 6-8. The limit of detection for Cu²⁺ (0.77 μM) is well under the allowable limit prescribed by the United States Environmental Protection Agency. Two metal (Cu²⁺ /Hg²⁺ ) ions are needed per L for complete fluorescence quenching. The probe shows remarkable reversibility on treatment with Na₂ EDTA, making the protocol more economical for practical purposes. Paper strip coated with the L solution of EtOH can detect the presence of Cu²⁺ and Hg²⁺ ions in the sample by visible quenching of the fluorescence intensity. DFT-TDDFT calculations support experimental observations, and d-orbitals of Cu²⁺ /Hg²⁺ provide a non-radiative decay pathway. Cell imaging study using HDF and MDA-MB-231 cells also supported the viability of L in detecting Cu²⁺ and Hg²⁺ ions in living cells.

A Review on Organic Colorimetric and Fluorescent Chemosensors for the Detection of Zn(II) Ions

Organic compounds display several electronic and structural features which enable their application in various fields, ranging from biological to non-biological. These compounds contain heteroatoms like sulfur, nitrogen and, oxygen, which provide coordination sites to act as ligands in the field of coordination chemistry and are used as chemosensors to detect various metal ions. This review article covers different organic compounds including Schiff bases, thiourea, pyridine, rhodamine, triazole, pyrene, coumarin, imidazole, diaminomaleonitrile, naphthoxazole, pyrimidine, thiophene, thioether, and other functional groups based chemosensors that contain heteroatoms like sulfur, nitrogen and, oxygen for fluorimetric and colorimetric detection of Zn(II) ions in different environmental, agricultural, and biological samples. Further, the sensing performances of these chemosensors have been compared and discussed which could help the readers for the future design of organic fluorescent and colorimetric chemosensors for the detection of Zn(II) ions. We hope this study will support the new thoughts to design a simple, efficient, selective, and sensitive chemosensor for the detection of Zn(II) ions in different samples (environmental, agricultural, and biological).

A green polyol approach for the synthesis of Cu2O NPs adhered on graphene oxide: a robust and efficient catalyst for 1,2,4-triazole and imidazo[1,2-a]pyridine synthesis

Cu2O NPs immobilized on graphene oxide are used as a heterogeneous catalyst for the synthesis of a series of 1,2,4-triazoles and imidazo[1,2-a]pyridines under solvent-free conditions.

Two- and three-photon excitable quaternized imidazo[1,2-a]pyridines as mitochondrial imaging and potent cancer therapy agents

We have synthesized a series of quaternized imidazo[1,2-a]pyridines in three steps from commercially available reagents. These compounds exhibit blue fluorescence emission at around 425 nm with good quantum yields. In addition, one specific compound was found to work as not only a two- and three-photon excitable mitochondria imaging agent, but also a therapeutic agent upon continuous irradiation conditions.

A highly selective multi-responsive fluorescence sensor for Zn2+ based on a diarylethene with a 4,6-dimethylpyrimidine unit

A novel turn-on mode fluorescent diarylethene containing a 4,6-dimethylpyrimidine unit was developed to fluorescently sense Zn2+. Its multiple-responsive properties induced by Zn2+/EDTA and ultraviolet/visible light have been systematically studied. The fluorescence sensor could efficiently detect Zn2+ with a 10 times enhancement of emission intensity and fluorescence color change (dark-green). In addition, the sensor showed clear discrimination from Cd2+. The limit of detection of the sensor was measured to be 8.48 × 10-8 mol L-1 for Zn2+. Finally, a molecular logic circuit was fabricated with the emission at 528 nm as the output signal and light and chemical stimuli as input signals.

A fluorescence probe based on 6-phenylimidazo[2,1-b]thiazole and salicylaldehyde for the relay discerning of In3+ and Cr3+

A new fluorescence probe, (E)-N′-(2-hydroxybenzylidene)-6-phenylimidazo[2,1-b]thiazole-3-carbohydrazide (LB1), based on 6-phenylimidazo[2,1-b]thiazole and salicylaldehyde was designed and synthesized.

Novel Diarylethene-Based Fluorescent Switching for the Detection of Al3+ and Construction of Logic Circuit

A novel photochromic diarylethene was synthesized successfully containing a phthalazine unit. Its multistate fluorescence switching properties were investigated by stimulating with UV/vis lights and Al3+/EDTA. The synthesized diarylethene displayed excellent selectivity to Al3+ with a distinct fluorescence change, revealing that it could be used as a sensor for fluorescence identification of Al3+, and a logic circuit was constructed by utilizing this diarylethene molecular platform. Moreover, it also exhibited a high accuracy for the determination of Al3+ in practical water samples.

A dual functional fluorescent sensor for the detection of Al3+ and Zn2+ in different solvents

A new fluorescent sensor, X, was designed and synthesized based on imidazo[2,1-b]thiazole and 2-hydroxy-1-naphthaldehyde, which could be used to detect Al³⁺ in methanol buffer solution and detect Zn²⁺ in ethanol buffer solution, respectively.

A new fluorescent sensor containing glutamic acid for Fe3+ and its resulting complex as a secondary sensor for PPi in purely aqueous solution

A new fluorescence sensor L with benzimidazo[2,1-α]benz[de]isoquinoline-7-one as the fluorophore and glutamic acid moiety as the receptor was synthesized and characterized.

Imine-functionalized thioether Zn(ii) turn-on fluorescent sensor and its selective sequential logic operations with H2PO4−, DFT computation and live cell imaging

Thioether Schiff base (H₂L), a nontoxic Zn²⁺-sensor (LOD, 0.050 μM) has shown selective ON–OFF emission following INHIBIT logic circuit with H₂PO₄⁻and useful agent for the identification of Zn²⁺and H₂PO₄⁻in intracellular fluid in living cells.