Fluoride Ion Sensor Research Articles

Boron Complexes of Oxasmaragdyrin, a Core-Modified Expanded Porphyrin

We report the synthesis of first examples of BF(2) and B(OR)(2) complexes of oxasmaragdyrin, the expanded core-modified porphyrin, in decent yields under very simple reaction conditions at room temperature. The boron complexation of oxasmaragdyrin alters the electronic properties of the macrocycle significantly as evident by various spectroscopic techniques. Our preliminary studies indicated that the B(OH)(2)-smaragdyrin complex can act as a selective neutral fluoride ion sensor.

Norharmane: Old yet highly selective dual channel ratiometric fluoride and hydrogen sulfate ion sensor

Norharmane provides a simple unexplored class of anion receptor, that allows for the ratiometric selective detection of F(-) and HSO(4)(-) ions. The presence of a strong base can easily form hydrogen bonds with the acidic hydrogen bond donor moiety and the relatively strong acid can easily protonate the basic hydrogen bond acceptor moiety, which can modulate the optical response and can detect the anions efficiently with high selectivity. In view of that, it is promising to conceive the use of these systems in various sensing applications as well as in other situations, such as anion transport and purification, where the availability of cheap and easy-to-make anion receptors, would be advantageous.

A specific chemodosimeter for fluoride ion based on a pyrene derivative with trimethylsilylethynyl groups

Pyrene derivative 1 containing four trimethylsilylethynyl substituents was synthesized and investigated as a chromogenic and fluorescent chemodosimeter sensor for fluoride ions. 1 showed a high sensitivity and specific selectivity over a rapid response time toward fluoride anions compared to other anions, such as Cl(-), Br(-), ClO(4)(-), H(2)PO(4)(-) and HPO(4)(2-). TD-DFT calculations showed that the delocalization of the σ-electrons of the silicon destabilized the HOMO energy level of 1, thus red shifting both its absorption and emission spectrum. The addition of F(-) removed the trimethylsilyl substituents and resulted in a blue shift of both the absorption and fluorescent spectra of 1, which could be monitored by the color change with the naked-eye. Moreover, an easy to prepare test paper, which was obtained by immersing a filter paper into a THF solution of 1, could be utilized to detect and estimate the concentration of fluoride anions in water.

A Rapid Aqueous Fluoride Ion Sensor with Dual Output Modes

The color purple: A siloxy-functionalized benzamide (see picture) is a highly efficient fluoride ion sensor in water. The sensor, which is activated when the OSi bond is cleaved by fluoride ions, provides two independent modes for signal recognition. In colorimetric mode, the fluoride ion concentration is transformed into a fluorescence signal that can be observed directly with the naked eye.

A class of fascinating optoelectronic materials: Triarylboron compounds

Triarylboron compounds are significant optoelectronic materials due to their excellent emissive and electron-transport properties, and could be applied in organic light-emitting diodes as emissive and/or electron-transport layers. Triarylboron compounds have vacant pπ orbital and have received increasing interest as fluoride ion and cyanide ion sensors utilizing specific Lewis acid-base interaction. This review summarizes their structural characteristics, optical properties and applications in chemosensors for anions and optoelectronic devices developed in recent years and discusses the problems and prospects.

A new fluoride ion colorimetric sensor based on dipyrrolemethanes

Colorimetric fluoride ion sensors were developed using dipyrrolemethanes 1– 4 synthesized from the reaction of aldehydes and pyrrole. The sensors showed a color change upon addition of fluoride ion with a substantial bathochromic shift. No significant color change was observed upon addition of any other anions. The significant changes of absorption bands and color show that chemosensor is selective toward fluoride ion over other anions such as Br −, Cl −, NO 3 −, HSO 4 −, SO 4 2−, AcO − and H 2PO 4 −. The binding constants of sensors with fluoride ion were obtained in the order of ∼10 2 which is enough to detect the fluoride ion.

Simple and efficient colourimetric F- sensors and a test paper for fluorine

A series of colourimetric fluoride ion sensors bearing azo-phenolic hydroxyl and Schiff base groups were synthesised. In CH3CN solutions, these sensors showed colourimetric single selectivity for F-. An easy-to-prepare test paper based on the sensor was developed, which could colourimetrically conveniently detect fluoride ion.

Simple colorimetric fluoride sensors based on nitrophenyl derivatives

Easy to prepare fluoride ion sensors bearing OH and NH groups as binding sites and nitrophenyl group as a chromophore [2-[(4-nitrophenylimino)methyl]-4-methylphenol (1), 2-[(4-nitrophenylamino)methyl]-4-methylphenol (2), 2-[(2,4-dinitrophenylimino)methyl]-4-methylphenol (3) and 2-[(2,4-dinitrophenylamino)methyl]-4-methylphenol (4)] were synthesised and characterised. The visible colour changes, the UV–vis and 1H NMR spectral changes towards anions were studied. The sensing ability of the receptor depends on the presence of electron-withdrawing group attached to the receptors and extended conjugation in the receptor framework and the order of the sensing ability is found to be 3>1>4>2 based on binding constant.

Highly Emissive Diborylphenylene‐Containing Bis(phenylethynyl)benzenes: Structure–Photophysical Property Correlations and Fluoride Ion Sensing

A series of 2,5-bis(dimesitylboryl)-1,4-bis(arylethynyl)benzenes 1-6 that contain various p-substituents on the terminal benzene rings, including NPh(2) (1), OMe (2), Me (3), H (4), CF(3) (5), and CN (6) groups, were synthesized, and the effects of the p-substituents on the absorption and fluorescence properties were investigated both in solution and in the solid state. Linear relationships were obtained not only between the Hammett sigma(p)(+) constants of the p-substituents and the absorption and fluorescence maxima, quantum yields, and excited-state dynamics parameters in solution, but also between the sigma(p)(+) constants and the fluorescence quantum yields in the solid state. An important finding extracted from these results is that the suppressed fluorescence quenching in the solid state is a common feature for the present laterally boryl-substituted pi-conjugated skeletons. Hence, the diborylphenylene can serve as a useful core unit to develop highly emissive organic solids. In fact, most of the derivatives showed more intense emission in the solid state than in solution. In addition to these studies, the titration experiment of 1 by the addition of nBu(4)NF was conducted, which showed the stepwise bindings of two fluoride ions with high association constants as well as a drastic change in the fluorescence spectra, while constantly maintaining high quantum yields (0.61-0.76), irrespective of the binding modes. This result also demonstrated the potential utility of the present molecules as an efficient fluorescent fluoride ion sensor.

Impact of Donor−Acceptor Geometry and Metal Chelation on Photophysical Properties and Applications of Triarylboranes

Three-coordinate organoboron compounds have recently found a wide range of applications in materials chemistry as nonlinear optical materials, chemical sensors, and emitters for organic light-emitting diodes (OLEDs). These compounds are excellent electron acceptors due to the empty p(pi) orbital on the boron center. When accompanied by electron donors such as amines, these molecules possess large electronic dipoles, which promote donor-acceptor charge-transfer upon excitation with light. Because of this, donor-acceptor triarylboranes are often highly luminescent both in the solid state and in solution. In this Account, we describe our research to develop donor-acceptor triarylboranes as efficient blue emitters for OLEDs. Through the use of hole-transporting donor groups such as 1-napthylphenylamines, we have prepared multifunctional triarylboranes that can act as the emissive, electron transport, or hole transport layers in OLEDs. We have also examined donor-acceptor compounds based on 2,2'-dipyridylamine or 7-azaindolyl donors, several of which have fluorescent quantum efficiencies approaching 100%. We are also investigating the chemistry of metal-containing triarylboranes. Our studies show that the electron-deficient boryl group can greatly facilitate metal-to-ligand charge-transfer transitions and phosphorescence. In addition, electronegative linker groups such as 2,2'-bipyridine can act in synergy with metal chelation to greatly improve the electron-accepting ability and Lewis acidity of triarylboranes. Donor-acceptor triarylboranes developed in our laboratory can also serve as a series of "switch-on" sensors for fluoride ions. When the donor and acceptor are linked by rigid naphthyl or nonrigid silane linkers, donor-acceptor conjugation is disrupted and charge transfer occurs primarily through space. The binding of fluoride ions to the boron center disrupts this charge transfer, activating alternative pi --> pi* transitions in the molecule and changing the emission color of the sample. More recently, we have used these nonconjugated linkers to prepare organometallic donor-acceptor triarylboranes in which fluorescence and phosphorescence can simultaneously be observed from two different chromophores in the same molecule at ambient temperature. These dual emissive molecules remain sensitive to fluoride ions, and give synergistic singlet-triplet emission responses when titrated with F(-). Fluoride ions can also act as valuable chemical probes, providing insight into the electronic structure of this new class of optoelectronic materials. We have demonstrated that donor-acceptor triarylboranes are promising materials in anion sensing and electroluminescent device applications. Nonetheless, despite our work and that of other research groups, there is still much to be learned about organometallic and multiply emissive triarylboron systems.

A novel, simple, colorimetric receptor based on 2′,4′-dinitrophenylhydrazone for acetate ion in organic medium

A novel 1,3-di(2′,4′-dinitrophenylhydrazone)-5-nitrobenzene receptor has been synthesized by simple steps with good yields. The anion recognition properties were studied by ultraviolet-visible (UV-Vis) spectroscopy. The results showed that the receptor had a higher affinity to F−, CH3COO− and H2PO 4 − , but no evident binding with Cl−, Br−, and I−. Upon addition of the three former anions to the receptors in dimethyl sulphoxide (DMSO) at 298.2 ± 0.1 K, the solution exhibited an obvious color change from yellow to mauve that could be observed by the naked eye, thus the receptor could act as a fluoride ion sensor even in the presence of other halide ions. The UV-Vis data indicates that a 1:1 stoichiometry complex formed through hydrogen-bonding interactions between receptor and anions. The hydrogen bond between phenylhydrazone –NH and acetate or fluoride anion was determined on the basis of 1H nuclear magnetic resonance (NMR) experiments.

A highly sensitive colorimetric and ratiometric sensor for fluoride ion

A new benzoimidazole-naphthalimide derivative 4 was synthesized and its photophysical properties were studied. This compound showed highly selectively and sensitive colorimetric and ratiometric sensing ability for fluoride anion.

Colorimetric Fluoride‐Anion Sensor Based on Intramolecular Hydrogen Bonding and Enol–Keto Tautomerization of a Phenothiazine Derivative

AbstractA colorimetric sensor for fluoride ions based on a new sensing mechanism is reported. The colorimetric sensor contains an isomerizable enol–keto moiety as the recognition site and phenothiazine as chromogenic center. A color change visible to the naked eye is observed upon addition of fluoride ions to the solution of sensor 1 in aprotic solvents such as CHCl3 and MeCN. The sensor shows no colorimetric response for other halide ions. Enol‐keto tautomerization is proposed to be responsible for the anion sensing of 1, based on UV/VIS absorption, 1H‐NMR, and single‐crystal structure analysis.

A ditopic colorimetric sensor for fluoride ion based on thiourea mercury complex

A novel ditopic chromogenic receptor, N-5-(8-hydroxy)quinoline- N′-4′-nitro-phenyl thiourea ( 1), was synthesized. The metal complex 1-Hg 2+ showed sensitive and highly selective responses to F − over other anions such as CH 3CO 2 −, H 2PO 4 −, HSO 4 − and Cl −. 1-Hg 2+–F − complex formed, which promoted the intramolecular charge transfer and led to a dramatic spectral change. The color of 1-Hg 2+ solution changed from colorless to red upon addition of F −. Thus, a colorimetric assay of F − was developed in acetonitrile by naked-eye detection. F − behaved linearly in the 8.0 × 10 −6 to 2.0 × 10 −5 mol L −1 concentration range with LOD as 1.4 × 10 −6 mol L −1.

Optically Highly Selective Sensing of Fluoride Ion by N3 Dye

The N3 dye, cis-Ru(H2dcbpy)2(NCS)2 (H2dcbpy=4,4′-dicarboxy-2,2′-bipyridyl), was demonstrated to be a highly selective luminescent and ratiocolorimetric sensors towards fluoride ion over chloride and bromide ions, by means of UV-Vis absorption and emission spectrophotometric titration method in dimethyl sulfoxide(DMSO) solution. A large "turn on" emission enhancement factor of 40, observed by the interaction of the N3 with fluoride ion was rather rare among the ruthenium complex-based fluoride ion sensors reported to date.

Colorimetric Fluoride Ion Sensing by Polyborylated Ferrocenes: Structural Influences on Thermodynamics and Kinetics

The thermodynamic factors underlying the use of ferroceneboronic esters as electrochemical or colorimetric fluoride ion sensors have been investigated through the synthesis of a range of systematically related derivatives differing in the number/nature of the boronic ester substituents and in the nature of ancillary ligands. Thus, if the shift in electrochemical potential associated with the conversion of one (or more) boronic ester group(s) to anionic boronate(s) on fluoride binding is sufficient to allow oxidation of the resulting host/guest complex by dioxygen, colorimetric sensing is possible. In practice, while monofunctional systems of the type CpFe[eta(5)-C(5)H(4)B(OR)(2)] offer selectivity in fluoride binding, electrochemical shifts in chloroform solution are insufficient to allow for a colorimetric response. Two chemical modification strategies have been shown to be successful in realizing a colorimetric sensor: (i) the use of the more strongly electron-donating Cp(*) ancillary ligand (which shifts the oxidation potential of both the free receptor and the resulting fluoride adduct cathodically by ca. -400 mV) and (ii) receptors featuring two or more binding sites and consequently a larger fluoride-induced electrochemical shift. Thus, in the case of [eta(5)-C(5)H(4)B(OR)(2)](2)Fe [(OR)(2) = OC(H)PhC(H)PhO, 2(s)], the binding of 2 equiv of fluoride gives an electrochemical shift (in chloroform) of -960 mV (cf. -530 mV for the corresponding monofunctional analogue, 1(s)). Related tris- and tetrakis-functionalized systems are also shown to be oxidized as the bis(fluoride) adducts, presumably because of fast oxidation kinetics, relative to the rate of the (electrostatically unfavorable) binding of a third equivalent of fluoride. Furthermore, the rate of sensor response (as measured by UV/vis spectroscopy) is found to be strongly enhanced by the presence of pendant (uncomplexed) three-coordinate boronic ester functions (e.g., a rate enhancement of 1-2 orders of magnitude for 3(s)/4(s) with respect to 2(s)) and/or delocalized aromatic substituents.

Phenol- and Catechol-Based Ruthenium(II) Polypyridyl Complexes as Colorimetric Sensors for Fluoride Ions

We report two ruthenium(II) polypyridyl complexes with pendant phenol/catechol functionality that act as colorimetric sensors for fluoride ions. Experiments have revealed that hydrogen bond formation occurs with a slight excess of fluoride ion. However, in higher [F-], deprotonation of the O-H functionality resulted. Time-dependent (TD-DFT) calculations at the B3LYP/LANL2DZ level have shown that new bands appear at longer wavelengths upon complexation with fluoride ions. These are of mixed character, MLCT (dpi(Ru)-->pi*(L1/bpy)), and intra- and interligand [pi(L1)-->pi*(bpy) and pi(L1)-->pi*(L1)] transitions. These complexes also act as sensors for fluoride ions in solvent-water mixtures.

Photophysical and Density Functional Studies of the Interaction of a Flavone Derivative with the Halides

The synthesis, photophysical behavior, and anion-sensing ability of a fluorescent molecular system, N-(3-methoxy-4-oxo-2-phenyl-4H-chromen-7-yl)-benzamide (1H), designed and developed with a view to sensing fluoride ions, are reported. NMR and density functional studies on the system have been carried out to determine the nature of the interaction between 1H and X- (X = halogen atom) responsible for fluoride-induced dramatic changes in the absorption and emission properties of 1H. The color change of 1H, which can be observed by the naked eye, is found specific to fluoride ion; it is unaffected by the presence of a large excess of Cl-, Br-, and I-, thus rendering 1H as a selective fluoride ion sensor in micromolar concentration in the visible region. The changes in the fluorescence behavior of 1H, specifically, the formation of an additional long-wavelength emission band in the presence of fluoride ion, allow ratiometric fluorescence signaling of the fluoride ion as well. The results suggest that abstraction of the acidic proton of 1H by the F- leading to the formation of 1- is responsible for the spectral changes that allow signaling of the F-. Density functional calculations of the optimized geometrical parameters and charge densities of the 1H...halide complexes confirm the proton abstraction mechanism of the signaling of F-. Calculations of the transition energies of the 1H, 1-, and 1H...F- (hydrogen-bonded complex) show that only 1- is responsible for the long-wavelength absorption and emission band observed in the presence of F-.

An Axial Subphthalocyanine as Ratiometric Fluoride Ion Sensor

Abstract A subphthalocyanine derivative (SubPc 1) with a naphthalimide fluorophore at the axial position was designed and synthesized for fluoride ion selective and sensitive sensing. The obvious changes in UV–vis and fluorescence spectra could be observed by naked eyes.

Dual chemosensing properties of new anthraquinone-based receptors toward fluoride ions

Novel colorimetric receptors 1-[(2-hydroxy-5-bromo-benzylidene)-amino]-anthraquinone, 1-[(2-hydroxy-5-methyl-benzylidene)-amino]-anthraquinone, and 1-[(2-hydroxy-5-nitro-benzylidene)-amino]-anthraquinone have been synthesized as fluoride ion sensors. A color change was observed visually (naked-eye) upon addition of fluoride ions in organic solvents to solutions of the receptors.