New type of tin(IV) complex based turn-on fluorescent chemosensor for fluoride ion recognition: elucidating the effect of molecular structure on sensing property

A novel type of chemosensor based on tin(IV) complexes incorporating hydroxyquinoline derivatives has been designed and investigated for selectively detecting fluoride ions. Sn(meq)2Cl2 (meq = 2-methyl-8-quinolinol) (complex 1) exhibits a significant enhancement in luminescence upon the introduction of fluoride ions. This enhancement greatly surpasses that observed with Snq2Cl2 and Sn(dmqo)2Cl2 (q = 8-hydroxyquinnoline; dmqo = 5,7-dimethyl-8-quinolinol). Furthermore, complex 1 displays excellent sensitivity and selectivity for fluoride detection in comparison to halides and other anions. As a result, complex 1 serves as an outstanding turn-on fluorescent chemosensor, effectively sensing fluoride ions. The Benesi-Hilderbrand method and Job's plot confirmed that complex 1 associates with F- in a 1 : 2 binding stoichiometry. Also, complex 1 exhibited a large binding constant (pKb = 10.4 M-2) and a low detection limit (100 nM). To gain a deeper insight into the photophysical properties and the underlying mechanism governing the formation of the tin(IV) fluoride complex via halide exchange, we successfully synthesized partially fluorinated Sn(meq)2F0.67Cl1.33 (2) and fully fluorinated Sn(meq)2F2 (3), all of which were characterized through computational studies, thereby elucidating their photophysical properties. DFT studies reveal that converting Sn(meq)2Cl2 to Sn(meq)2F2, an endergonic process, leads to greater stability due to reducing steric hindrance about the metal center. Furthermore, the fluorinated complex significantly increases dipole moment, resulting in high affinity toward the F- ion.

Imidazole fused phenanthroline (PIP) ligands for the preparation of multimodal Re(I) and 99mTc(I) probes

A small library of [2 + 1] 99mTc(i) complexes based on phenyl-imidazole-fused phenanthroline (PIP) ligands were synthesized and evaluated as multimodal molecular imaging probes. Using either a two-step or a one-pot synthesis method, 99mTc-PIP complexes containing N-methylimidazole as the monodentate ligand were prepared and isolated in good (54 to 89%) radiochemical yield, with the exception of one derivative bearing a strongly electron-withdrawing substituent. The stability of the [2 + 1] complexes was assessed in saline and in cysteine and histidine challenge studies, showing 6 hours stability, making them suitable for in vivo studies. In parallel, the Re(i) analogues were prepared as reference standards to verify the structure of the 99mTc complexes. The optical properties were consistent with other previously reported [2 + 1] type Re(i) complexes that have been used as cellular dyes and sensors. To facilitate the development of targeted derivatives, a tetrazine-PIP ligand was also synthesized. The 99mTc complex of the tetrazine PIP ligand effectively coupled to compounds containing a trans-cyclooctene (TCO) group including a TCO-albumin derivative, which was prepared as a model targeting molecule. An added benefit of the Re-PIP-Tz construct is that the emission from the metal complex was quenched by the presence of the tetrazine. Following the addition of TCO, there was a 70-fold increase in fluorescence emission, which can in future be leveraged during in vitro studies to reduce background signal.

Four-coordinated see-sawN-(aryl)-2-(propan-2-ylidene)hydrazinecarbothioamide complexes of nickel(ii), copper(ii) and zinc(ii) and their propensity for catalytic cyclisation

Four-coordinated metal complexes of two hydrazinecarbothioamide-derived ligands with divalent nickel, copper and zinc are described and the selective reactivity difference of copper(ii) to cyclise the ligand or to form a complex is described.

Luminescent Iridium(III) Chemosensor for Tandem Detection of F- and Al3

A new highly sensitive luminescent iridium(III) chemosensor, 1, was designed and synthesized for tandem detection of fluoride ions (F^-) and aluminum ions (Al³⁺). This sensor 1 exhibited obvious luminesce quenching by hydrogen bond interactions with F^-. In addition, the resulting 1-F complex can be further used to detect Al³⁺ through a luminesce enhancement. The detection limit (0.02 μM) of 1-F for Al³⁺ is far lower than the World Health Organization (7.41 μM) limit for drinking water. Importantly, chemosensor 1-F could be used to detect and quantify F^- and Al³⁺ reversibly. This sensor achieved rapid detection of two ions, which relies on only one probe.

Recent advances in 1,10-phenanthroline ligands for chemosensing of cations and anions

This review encompasses and highlights recent developments of 1,10-phenanthroline ligands behaving as a customized moiety used in recognition and sensing of cations and anions.

Fluorescent probes for the selective detection of chemical species inside mitochondria

This feature article systematically summarizes the development of fluorescent probes for the selective detection of chemical species inside mitochondria.

Highly selective fluorescence sensors for the fluoride anion based on carboxylate-bridged diiron complexes

The diiron–sulfur clusters bearing urea and anthracene units showed rapid and selective recognition for the fluoride ion.

Coumarin functionalized thiocarbonohydrazones as a new class of chromofluorescent receptors for selective detection of fluoride ion

Thiocarbonohydrazone receptors selectively recognize fluoride ionsviaH-bond interactions and subsequent deprotonation to elicit a distinct visual and fluorescence colour change.

Simultaneous enhancement of fluorescence and solubility by N-alkylation and functionalization of 2-(2-thienyl)imidazo[4,5-f][1,10]-phenanthroline with heterocyclic bridges

A family of TIP based aromatic heterocyclic compounds has been designed and synthesized by introducing alkyl chains and extended S-, N- and O-containing tails, where simultaneous enhancement of fluorescence and solubility has been achieved.

Detection of NaCN in aqueous media using a calixarene-based fluoroionophore containing ruthenium(ii)-bipyridine as the fluorogenic unit

A new fluoroionophore containing a Ru(ii)-bipyridine unit and a calixarene moiety is synthesized. It selectively detects CN⁻ from NaCN in aqueous media; its performance has been tested successfully in real samples.

Synthesis and characterization of monometallic rhenium(i) complexes and their application as selective sensors for copper(ii) ions

Monometallic Re(i) complexes, selective and sensitive sensor of Cu(ii) ion, show substantial enhancement in the emission intensity, quantum yield, and lifetime due to the restriction of CN isomerization.

Study on divalent copper, nickel and zinc model complexes for fluoride ion detection

A series of mononuclear hydroxyaromatic oxime metal complexes were synthesized for detection of fluoride ion and shown that the spectral signals of such complexes depend on the electronic configuration of the metal ion.

A catalyst-free approach to a novel imidazo [4,5-f][1,10] phenanthroline ligand and its corresponding ruthenium(ii) complex: insights into their applications in colorimetric anion sensing

Novel imidazo[4,5-f][1,10]phenanthroline ligand and its corresponding Ru(ii) complex are synthesized from green protocol for colorimetric detection of anions in water.

N,N-Diphenyl-4-(1H-pyrrolo[1,2-f][1,10]phenanthrolin-2-yl)aniline ethanol monosolvate

The title compound, C₃₂H₂₁N₄·C₂H₅OH, crystallized as an ethanol monosolvate. In the mol­ecule of this phenanthroline derivative, the pyridine rings are almost coplanar, making a dihedral angle of 1.54 (13)°. The tri­phenyl­amine group, introduced as an electron donor, shows a propeller-type structure, and the dihedral angles between the benzene rings are 68.71 11), 63.92 (16) and 70.81 (15)°. In the crystal, the phenanthroline mol­ecules are linked via the solvent mol­ecule by N—H⋯O, O—H⋯N and C—H⋯O hydrogen bonds, leading to the formation of zigzag chains propagating along [010]. These chains are linked via C—H⋯N hydrogen bonds, forming undulating two-dimensional networks extending in the a- and b-axis directions.

Highlights on contemporary recognition and sensing of fluoride anion in solution and in the solid state

The fluoride anion has recently gained well deserved attention among the scientific community for its importance in many fields of human activities, but also for concerns on its effect on health and the environment. Although surprisingly overlooked in systematic studies in the past, fluoride has nowadays become a topical target in the field of anion recognition. A multitude of scientific reports are published every year where the establishment of efficient and specific interaction with fluoride is sought in polar and aqueous media. Here, the emphasis is directed to a detailed description of the most interesting contemporary studies in the field, with a particular focus given to those published in the last few years.