A Bisferrocene-Benzobisimidazole Triad as a Multichannel Ditopic Receptor for Selective Sensing of Hydrogen Sulfate and Mercury Ions

Anion Sensing through Redox-Modulated Fluorescent Halogen Bonding and Hydrogen Bonding Hosts

Anion sensing via either optical or electrochemical readouts has separately received enormous attention, however, a judicious combination of the advantages of both modalities remains unexplored. Toward this goal, we herein disclose a series of novel, redox-active, fluorescent, halogen bonding (XB) and hydrogen bonding (HB) BODIPY-based anion sensors, wherein the introduction of a ferrocene motif induces remarkable changes in the fluorescence response. Extensive fluorescence anion titration, lifetime and electrochemical studies reveal anion binding-induced emission modulation through intramolecular photoinduced electron transfer (PET), the magnitude of which is dependent on the nature of both the XB/HB donor and anion. Impressively, the XB sensor outperformed its HB congener in terms of anion binding strength and fluorescence switching magnitude, displaying significant fluorescence turn-OFF upon anion binding. In contrast, redox-inactive control receptors display a turn-ON response, highlighting the pronounced impact of the introduction of the redox-active ferrocene on the optical sensing performance. Additionally, the redox-active ferrocene motif also serves as an electrochemical reporter group, enabling voltammetric anion sensing in competitive solvents. The combined advantages of both sensing modalities were further exploited in a novel, proof-of-principle, fluorescence spectroelectrochemical anion sensing approach, enabling simultaneous and sensitive read out of optical and electrochemical responses in multiple oxidation states and at very low receptor concentration.

Strategic Design of a 2,6-Disubstituted Pyridine-based Probe having Hard-Soft Centers: Responsive Divergence from One Core

Alkyne is a versatile functional group in organic chemistry, and is able to undergo a wide variety of reactions and interactions. Featuring a reactive functional group, alkyne participates in many...

Hydrogen bond regulated hydrogen sulfate ion recognition: an overview

Hydrogen sulfate possesses substantial biological importance, having a colossal impact on physiological and environmental events. Therefore, several scientific groups have devoted serious effort to the development of versatile colorimetric and fluorimetric HSO4- sensors. Along with the scope, challenges, and significance, this review emphasizes the advancement of the optical recognition of HSO4- based on hydrogen bonding during the past two decades. Moreover, hydrogen-bond-driven proton transfer, ESIPT, ICT, PET, CHEF, and TBET mechanisms that allow for the optical detection of HSO4- are also discussed concisely. The foundation of this review includes the key points of the sensing process, like the nature of spectroscopic changes, selectivity and sensitivity, naked-eye color changes, the reusability of sensors, and the in vivo detection of HSO4-, if any. Special attention is focused on the correlation between the photophysical changes and the underlying interaction mechanisms that triggered the recognition aspect.

Electrochemical Anion Sensing: Supramolecular Approaches

Anions play a vital role in a broad range of environmental, technological, and physiological processes, making their detection/quantification valuable. Electroanalytical sensors offer much to the selective, sensitive, cheap, portable, and real-time analysis of anion presence where suitable combinations of selective (noncovalent) recognition and transduction can be integrated. Spurred on by significant developments in anion supramolecular chemistry, electrochemical anion sensing has received considerable attention in the past two decades. In this review, we provide a detailed overview of all electroanalytical techniques that have been used for this purpose, including voltammetric, impedimetric, capacititive, and potentiometric methods. We will confine our discussion to sensors that are based on synthetic anion receptors with a specific focus on reversible, noncovalent interactions, in particular, hydrogen- and halogen-bonding. Apart from their sensory properties, we will also discuss how electrochemical techniques can be used to study anion recognition processes (e.g., binding constant determination) and will furthermore provide a detailed outlook over future efforts and promising new avenues in this field.

The first colorimetric receptor for the B4O72− anion based on nitro substituted phenanthroimidazole ferrocene derivatives

Four phenanthroimidazole ferrocene derivatives (2a–2d) were synthesized. Recognition of 12 anions by 2a–2d was investigated by UV-Vis absorption analysis, showing that 2b and 2d sensed B₄O₇²⁻ selectively with an obvious color change observed.

Ferrocenyl benzimidazole with carboxylic and nitro anchors as potential sensitizers in dye-sensitized solar cells

Two ferrocenyl benzimidazoles with carboxylic and nitro anchors were prepared and their light harvesting properties explored in dye-sensitized solar cells (DSSCs).

A fluorescence turn-on chemosensor for hydrogen sulfate anion based on quinoline and naphthalimide

A new fluorescence turn-on chemosensor 1 based on quinoline and naphthalimide was prepared and its anion sensing toward various anions behavior was explored in this paper. Sensor 1 exhibited a highly selective fluorescent response toward HSO4(-) with an 8-fold fluorescence intensity enhancement in the presence of 10equiv. of HSO4(-) in DMSO-H2O (1/1, v/v) solution. The sensor also displayed high sensitivity to hydrogen sulfate and the detection limit was calculated to be 7.79×10(-7)M. The sensing mechanism has been suggested to proceed via a hydrolysis process of the Schiff base group. The hydrolysis product has been isolated and further identified by (1)H NMR and MS.

A solo fluorogenic probe for the real-time sensing of SO32−and SO42−/HSO4−in aqueous medium and live cells by distinct turn-on emission signals

A fluorogenic probe (L) rendered rapid and differential turn-on responses to SO₃²⁻and SO₄²⁻/HSO₄⁻in aqueous medium.

Chemically-modified cellulose paper as smart sensor device for colorimetric and optical detection of hydrogen sulfate in water

The first portable, recyclable and highly selective paper-based sensor device for the colorimetric and optical detection of hydrogen sulfate anions in water has been developed.

An abiotic receptor and its Cu(II) complex as selective 'turn-off' chemosensor for bisulfate ion

The ligand 2,6-bis[(N-phenyl)amido]-4-methylphenol (receptor 1) and its copper(II) complex (receptor 2) having amide moiety have been designed and synthesized for selective sensing of anions. The anion recognition behavior of the receptor 1 and its copper complex (receptor 2) has been studied in acetonitrile. Quenching of fluorescence was observed for both receptors in presence of HSO4(-) anion whereas other physiologically and environmentally important anions such as F(-), Cl(-), Br(-), I(-), CN(-), OAc(-), HCO₃(-), H₂PO₄(-), NO₃(-), NO₂(-) and SO₄(2-) show fluorescence enhancement behavior. The sensing protocol has been studied both spectrophotometrically as well as spectrofluorometrically. Fluorescence quenching is suggested to proceed via both dynamic and static processes.

A case of oxoanion recognition based on combined cationic and neutral C–H hydrogen bond interactions

A bidentate bis-(benzimidazolium) receptor containing pyrene as fluorescent signaling units recognizes sulphate and hydrogenpyrophosphate in a competitive water–DMSO medium through combinations of cationic and neutral C–H hydrogen bonding.

A water soluble copper(ii) complex as a HSO4− ion selective turn-on fluorescent sensor applicable in living cell imaging

A water soluble non-fluorescent biofriendly cell permeable structurally characterised copper(ii) complex (1) selectively senses HSO₄⁻ ions as low as 3.18 × 10⁻⁷ M in water : DMSO (9 : 1, v/v) HEPES buffer at biological pH.

Squaramide-based lab-on-a-molecule for the detection of silver ion and nitroaromatic explosives

A squaramide based lab-on-a-molecule showed selective absorption enhancement and emission quenching towards Ag⁺ and nitroaromatic explosives, respectively in aqueous solution.

A bio-attuned ratiometric hydrogen sulfate ion selective receptor in aqueous solvent: structural proof of the H-bonded adduct

A new cell permeable quinazoline based receptor (1) behaves as a highly selective chemosensor for HSO₄⁻ ions at nanomolar concentration in aqueous medium by formation of the adduct [LHSO₄]⁻LH⁺·3H₂O confirmed by single crystal X-ray crystallography.

A simple and highly selective 2,2-diferrocenylpropane-based multi-channel ion pair receptor for Pb2+ and HSO4−

A 2,2-diferrocenylpropane-based multi-channel ion pair receptor 1 was designed and structurally characterized. It was a “naked-eye-detectable” chemosensor towards Pb²⁺ and HSO₄⁻ with excellent selectivity and sensitivity.

Multifunctional Benzothiadiazole-Based Small Molecules Displaying Solvatochromism and Sensing Properties toward Nitroarenes, Anions, and Cations

Aryl or heteroaryl 5-substituted imidazo-benzothiadiazole derivatives were synthesized and shown to display remarkable solvatofluorochromism and selectively sense mercury(II) cations, acetate anions, and nitroaromatic derivatives, with discrimination between p-nitrophenol and picric acid. These novel sensors are of importance these days, as the detection of explosives is a high priority in issues of national security and environmental protection. To determine the ion binding properties of the sensors, their absorption and fluorescence emission spectra upon binding different cations and anions were compared. Significant shifts in the spectra were only observed for mercury(II) and acetate. The binding of these two ions was further studied using (1)H NMR. The binding properties of different nitroaromatic compounds were also determined, and the results showed the importance of the presence of a phenol group in the guest molecule. Specifically, the two sensors were shown to discriminate between p-nitrophenol and picric acid. Finally, the mechanism of fluorescence quenching upon addition of nitrophenols was determined by computational methods.

Dual colorimetric sensing of mercury and iodide ions by steroidal 1,2,3-triazole-stabilized silver nanoparticles

Bile acid-based 1,2,3-triazole ligands have been synthesized, which show excellent ability to stabilize silver nanoparticles. These AgNPs have been found to exhibit highly selective dual colorimetric sensing of Hg²⁺ and I⁻ ions.

Highly sensitive and selective detection of the pyrophosphate anion biomarker under physiological conditions

Self-assembled monolayers on gold of a multidentate adsorbate bearing a bis(carbazolyl)urea unit are prepared and used as a surface resonance plasmon sensor for the detection of hydrogen pyrophosphate anions under physiological conditions.

Coumarin based dual switching fluorescent ‘turn-on’ chemosensor for selective detection of Zn2+ and HSO4−: an experimental and theoretical study

A coumarin based fluorescence ‘turn-on' chemosensor (HL) for the selective detection of Zn²⁺ and HSO^4¬ has been developed. Emission intensity of HL is enhanced by 27 and 17 fold in presence of Zn²⁺ and HSO^4¬ respectively. Theoretical study interprets the electronic structure and sensing mechanism of HL.

Bis(carbazolyl)ureas as selective receptors for the recognition of hydrogenpyrophosphate in aqueous media

Recognition properties of the novel bis(carbazole) tris-ureidic-based receptors 1 and 2 toward different anions have been studied by (1)H NMR and absorption and emission spectroscopy, as well as by DFT calculations. Receptor 1, in which the two urea-functionalized arms are decorated with p-nitrophenyl rings, behaves as a highly selective chromogenic molecular probe for hydrogenpyrophosphate anion in a competitive medium (acetonitrile/water, 70/30). Receptor 2, bearing two urea arms decorated with photoactive pyrenyl rings, acts as a highly selective fluorescent molecular probe for hydrogenpyrophosphate anion in either acetonitrile or an aqueous mixture (acetonitrile/water, 85/15). Receptor 2 exhibits a dual monomer-excimer emission spectrum and undergoes a remarked ratiometry in acetonitrile in the presence of hydrogenpyrophosphate: the excimer band disappears, whereas the monomer band is slightly increased. However, in the aqueous mixture, a strong increase of the excimer emission band was observed, while the monomer emission bands remained almost unaffected. The resulting binding modes and spectroscopic features are explained by suitable structures of model complexes for both receptors. In such complexes, a peripheral cooperative effect was found, alleviating the excess of negative charge in the guest toward the outer surface of the host, as well as the required enlargement on its internal cavity.

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the years 2010-2011

This review focuses on examples reported in the years 2010-2011 dealing with the design of chromogenic and fluorogenic chemosensors or reagents for anions.