Anion receptor chemistry: highlights from 1999

Solvent media as the driving force in the formation of one-dimensional silver(I) coordination polymers with 2-methylidene-1,3-bis(nicotinoyloxy)propane

Two kinds of silver(I) coordination polymers consisting of the same chemical composition, [Ag(CF3SO3)(L)] [L is 2-methylidene-1,3-bis(nicotinoyloxy)propane], were synthesized and characterized by infrared (IR) and photoluminescence (PL) spectroscopy, elemental and thermal analyses, and single-crystal X-ray diffractometry; these are catena-poly[[(trifluoromethanesulfonato-κO)silver(I)]-μ-2-methylenepropane-1,3-diyl dinicotinate-κ2 N:N′], [Ag(CF3SO3)(C16H14N2O4)] n , and its chloroform monosolvate, {[Ag(CF3SO3)(C16H14N2O4)]·CHCl3} n . The X-ray crystallographic measurements revealed that the silver(I) compounds exhibit one-dimensional sinusoidal or helical molecular structures depending on the solvent used for crystallization. Self-assembly in a methanol/chloroform mixture produces the sinusoidal molecular strand, whereas recrystallization from acetonitrile medium affords a racemic mixture of the helical strands. These compounds display a fluorescence emission arising from both the ligand-centred transition and the ligand-to-metal charge transfer (LMCT) in the solid state under ambient conditions.

Thiourea- and Amino-Substituted Benzoxadiazole Dyes with Large Stokes Shifts as Red-Emitting Probe Monomers for Imprinted Polymer Layers Targeting Carboxylate-Containing Antibiotics

Bifunctional fluorescent molecular oxoanion probes based on the benzoxadiazole (BD) chromophore are described which integrate a thiourea binding motif and a polymerizable 2-aminoethyl methacrylate unit in the 4,7-positions of the BD core. Concerted charge transfer in this electron donor-acceptor-donor architecture endows the dyes with strongly Stokes shifted (up to >250 nm) absorption and fluorescence. Binding of electron-rich carboxylate guests at the thiourea receptor leads to further analyte-induced red-shifts of the emission, shifting the fluorescence maximum of the complexes to ≥700 nm. Association constants for acetate are ranging from 1-5×105  M-1 in acetonitrile. Integration of one of the fluorescent probes through its polymerizable moiety into molecularly imprinted polymers (MIPs) grafted from the surface of submicron silica cores yielded fluorescent MIP-coated particle probes for the selective detection of antibiotics containing aliphatic carboxylate groups such as enoxacin (ENOX) at micromolar concentrations in highly polar solvents like acetonitrile.

Quinoline based thiosemicarbazones as colorimetric chemosensors for fluoride and cyanide ions and DFT studies

High toxicity and extensive accessibility of fluoride and cyanide ions in diverse environmental media encouraged attention for scheming well-organized probes for their detection. Keeping in mind we have designed and synthesized thiosemicarbazone-based chemosensors RB-1, RB-2 and RB-3 for the detection of fluoride and cyanide ions. The structural elucidation of the synthesized chemosensors is done by employing different analytical techniques including nuclear magnetic resonance and electronic absorption specrtoscopies. Admirable detection limit, binding constant and fast response time (2 s) to F- and CN- ions enlarged the applications of these chemosensors. Additional confirmation of the sensing ability of these chemosensors is derived from DFT and TDDFT calculations with M06/6-311G(d,p) method by performing FMO, UV-Vis, QTAIM and global reactivity parameters elucidation. Overall results point out that investigated chemosensors are suitable candidates for sensing the F- ions. These chemosensors were successfully applied to detect F- ions in a commercial toothpaste sample.

Fluorescent Chemosensors Based on Polyamine Ligands: A Review

Polyamine ligands are water-soluble receptors that are able to coordinate, depending on their protonation degree, either metal ions, anionic, or neutral species. Furthermore, the presence of fluorescent signaling units allows an immediate visual response/signal. For these reasons, they can find applications in a wide variety of fields, mainly those where aqueous media is necessary, such as biological studies, wastewater analysis, soil contamination, etc. This review provides an overview of the recent developments in the research of chemosensors based on polyamine ligands functionalized with fluorescent signaling units. The discussion focuses on the design, synthesis, and physicochemical properties of this type of fluorescent chemosensors in order to analyze the applications associated to the sensing of metal ions, anions, and neutral molecules of environmental and/or biological interest. To facilitate a quick access and overview of all the chemosensors covered in this review, a summary table of the chemosensor structures and analytes, with all the corresponding references, is also presented.

Anion-Recognition Studies of a Rhenium(I) 4-Mercaptopyridine Compound and Its Ligand-Coupling Products

The reaction of Re(CO)₅Cl with 4-mercaptopyridine (4-PySH) led to the formation of [Re(CO)₃(4-HPyS)₃]Cl (1), showing three hydrogen-bonding donors of 4-PySH ligands as well as a characteristic ligand-to-metal charge-transfer absorption at ca. 380 nm. In this regard, a variety of anions, i.e., CN^-, OAc^-, F^-, Cl^-, Br^-, I^-, PF₆^-, NO₃^-, ClO₄^-, and H₂PO₄^-, were examined to study anion-recognition studies through hydrogen-bonding functionalities. Upon the addition of CN^- to a methanolic solution of complex 1, a remarkable spectral change with an isosbestic point at ca. 314 nm in the absorption spectra was observed, with a binding constant (K_b) calculated to be 24770 M^-1. Moreover, the OAc^- anion also shows a similar trend, but a mild spectral change, with K_b calculated to be 2170 M^-1. Unlike those of CN^- and OAc^-, the addition of F^-, Cl^-, Br^-, and I^- anions causes a less pronounced spectral change with an isosbestic point at ca. 350 nm and K_b calculated to be 2863-750 M^-1. However, almost no spectral change can be observed for other anions (i.e., PF₆^-, NO₃^-, H₂PO₄^-, and ClO₄^-). Interestingly, the molecular loops of [Re(CO)₃Cl(Py₂S₂)]₂ (2; Py₂S₂ = 4,4'-dipyridyl disulfide) and [Re(CO)₃Cl(Py₂S)_0.35(Py₂S₂)_0.65]₂ (3; Py₂S = 4,4'-dipyridyl sulfide) can be isolated and structurally characterized by X-ray diffraction, where those crystals were grown from diethyl ether diffusion into a methanolic solution of complex 1 with [Bu₄N]CN and [Bu₄N]NO₃, respectively. It is noted that such unusual ligand-coupling reactions toward the homoligand and hybrid-ligand loops of complexes 2 and 3 can be achieved at room temperature in this study.

Anion-binding-induced and reduced fluorescence emission (ABIFE & ABRFE): A fluorescent chemo sensor for selective turn-on/off detection of cyanide and fluoride

A new hydrazine based π-hole assisted, electron deficient turn-on/off fluorescent and colorimetric sensor L with anion-binding induced/reduced fluorescent emission (ABIFE & ABRFE) has been designed and synthesized. The prepared sensor L exhibited excellent turn-on fluorescence emission in the presence of cyanide ion through ABIFE. On the other hand, the receptor L turns-off its fluorescence intensity upon binding with fluoride; however, the reduced emission intensity of this complex of L is recovered by addition of cyanide. The sensor L is almost intact with other tested anions. To the best of our knowledge, this is the first report on sensing of cyanide and fluoride by a neutral hydrazine based receptor via anion-binding-induced fluorescence emission (ABIFE) and anion-binding-reduced fluorescence emission (ABRFE) mechanisms respectively. The observed ABIFE and ABRFE phenomena of L with cyanide is further supported by UV-Vis, Emission, ¹H NMR and IR spectroscopic studies.

Potentiometric Carboxylate Sensors Based on Carbazole-Derived Acyclic and Macrocyclic Ionophores

Solid-contact ion-selective electrodes with carbazole-derived ionophores were prepared. They were characterized as acetate sensors, but can be used to determine a number of carboxylates. The potentiometric response characteristics (slope, detection limit, selectivity, and pH sensitivity) of sensors prepared with different membrane compositions (ionophore, ionophore concentration, anion exchanger concentration, and plasticizer) were evaluated. The results show that for the macrocyclic ionophores, a larger cavity provided better selectivity. The sensors exhibited modest selectivity for acetate but good selectivity for benzoate. The carbazole-derived ionophores effectively decreased the interference from lipophilic anions, such as bromide, nitrate, iodide, and thiocyanate. The selectivity, detection limit, and linear range were improved by choosing a suitable plasticizer and by reducing the ionophore and anion exchanger concentrations. The influence of the electrode body’s material upon the composition of the plasticized poly(vinyl chloride) membrane, and thus also upon the sensor characteristics, was also studied. The choice of materials for the electrode body significantly affected the characteristics of the sensors.

Flexibility and anion exchange of [(X)@Pd2L4] cages for recognition of size and charge of polyatomic anions

The self-assembly of Pd(NO3)2 with L (L = 1,2-bis(dimethyl(pyridin-3-yl)silyl)ethane) gives rise to [PdL2](NO3)2 in high yields. Anion exchange of [PdL2](NO3)2 with X- (X- = BF4-, ClO4-, and PF6-) changes the skeleton into a cage of [(X)@Pd2L4](X)3. Successive anion exchange of [(X)@Pd2L4](X)3 (X- = BF4-, ClO4-, and PF6-) with X- (X- = ReO4- and SiF62-) produces [(ReO4)@Pd2L4](ReO4)3 and [(SiF6)@Pd2L4](SiF6), respectively, irrespective of anion charge. The flexible nature and conformation of cages are significantly dependent on the nestled polyatomic anions. Thus, this system can be used as a molecular recognizer of the size and charge of ubiquitous polyatomic anions.

Hexafluorosilicate anion in the formation of a coordination cage: anion competition

The construction of a coordination cage in a system of dual anions including hexafluorosilicate was investigated. Significant catalytic effects on catechol oxidation catalysis performance ranks among the most efficient yet recorded.

Diverse anion exchange of pliable [X2@Pd3L4]4+ double cages: a molecular ruler for recognition of polyatomic anions

Reaction of Pd(BF4)2 with L (L = bis(pyridin-3-yl-propyl)pyridine-3,5-dicarboxylate) in the 1 : 2 mole ratio gives rise to a spiro-type [PdL2]·(BF4)2·2C6H6·2CH3CN, and further self-assembly of [PdL2]·(BF4)2·2C6H6·2CH3CN with Pd(NO3)2 in the 2 : 1 mole ratio in Me2SO at 90 °C produces a uniquely pliable double cage of [(NO3)2(H2O)2@Pd3L4](BF4)4·6C3H7NO. Both the encapsulated NO3- and the outside BF4- anions are exchanged by X- to form [(X)2@Pd3L4](X')4 (X- = PF6-, ClO4-, and/or NO3-; X'- = BF4-, PF6-, ClO4-, and NO3-) with all-inclusive pure or mixed anions. The pliable and characteristic properties of the double cages were confirmed by anion exchange of the nestled or outside anions in the present study. This system can be used as a ruler for recognition of ubiquitous polyatomic anions.

Dynamic optical activity induction in the N-alkyl-N'-trityl ureas and thioureas

Considered to be rigid, the urea and thiourea functionalities, often used in material chemistry and in asymmetric organocatalysis, are able to transmit information regarding 3D structure from a permanently chiral inducer part to a dynamically chiral (reporter) part of the molecule. Despite a considerable distance between the inducer and the reporter parts of the molecule, the chirality transfer phenomenon has been demonstrated for a series of secondary N-alkyl-N'-trityl ureas and thioureas. The induction of helicity in a stereodynamic trityl propeller is revealed by rising non-zero Cotton effects in the area of trityl absorption. The information regarding the 3D structure of the inducer is transferred to the reporter part of the system through a set of weak but complementary electrostatic interactions. The presence of two supramolecular motifs in the same molecule, characterized by opposite properties, significantly affected the molecular solid state structure of the thioureas and their abilities to assemble. In the crystalline phase, the model, a chiral N-tert-butyl-thiourea derivative that retains the extended Z,Z conformation of the linker, is prone to form a supramolecular network typical of secondary ureas and thioureas. In contrast, the presence of the hydrophobic trityl group suppresses the thioamide NHS[double bond, length as m-dash]C hydrogen bonds. Therefore, trityl acts as a supramolecular protecting group for thioamide functionality, hampering the formation of hydrogen bonded networks in the solid state.

Manipulation of Water for Diversified Functionalization of Tetrahydro-β-carbolines (THβCs) with Indoles

Water plays a crucial role in organic synthesis. However, diversified functionalization manipulated by water is still rare and remains unexplored. Herein, we report the first water-manipulated protocol to achieve the diversified functionalization of tetrahydro-β-carbolines (THβCs) in an open flask at room temperature that exhibit a broad functional-group tolerance. More water leads to monoarylation, while less water leads to diarylation. Further one-step transformation afforded oxidized bis(indolyl)methanes, eudistomin U, and the related derivatives in satisfactory yields.

Isophthaloyl-Based Selective Fluorescence Receptor for Zn (II) Ion in Semi-Aqueous Medium

A novel Isophthaloyl-based symmetrical (12E,21E)-N1',N3'-bis(2-hydroxybenzylidene) isophthalohydrazide, receptor (1) was synthesized and characterized using various spectroscopic technique. The reorganization ability of receptor (1) was evaluated in semi-aqueous medium and shows significant enhancement in fluorescence intensity for Zn (II) ion over various metal ions in CH₃CN:H₂O (1:1, v/v). The 1:2 binding stoichiometry between receptor (1) and Zn (II) ion was established using Job's plot and the proposed complex structure was calculated by applying Density Functional Theory (DFT) method. The binding constant (K_a) of receptor (1) with Zn (II) ion was established with the Benesi-Hildebrand plot, Scatchard and Connor's plot and the values are 1.00 × 10⁴ M^-1, 1.05× 10⁴ M^-1 and 1.05× 10⁴ M^-1 respectively. The limit of detection (LOD) and limit of quantification (LOQ) of receptor (1) and Zn (II) ion was 0.292 μM and 0.974 μM respectively. The binding mode was due to photo-induced electron transfer (PET) and the coordination of Zn (II) ion with C = N hydroxyl group of receptor (1). Electrochemical analysis of metal free receptor (1) and with Zn (II) ion also confirmed the formation of complex.

Tuning the recognition properties of urea based receptor towards cyanide in aqueous medium: Effect of fluorine substitution on strength and selectivity of the anion receptor

In this report, we have successfully tuned the selectivity and sensitivity of an anion receptor L¹ by substituting electron withdrawing natured fluorine atoms directly on to the rim of the phenyl ring. Despite the fact that, we have two electron withdrawing natured nitro substituents on the other side of receptor L¹; two fluorine substitutions made dramatic change in the sensing ability as well as the selectivity of the receptor L¹ towards anions. The acetonitrile solution contains L¹ with tetrabutyl ammonium salts of fluoride, cyanide, acetate and dihydrogen phosphate results sudden color changes from yellow to brown; almost negligible spectral/color change for azide and bifluoride, where as there is no color change observed with any other anionic guests with L¹. Solution state binding studies of L¹ are carried out by UV-Vis spectrometry titration in 100% acetonitrile and it is found to be the receptor L¹ selectively binds cyanide, phosphate and fluoride stronger than acetate; it is also found that receptor binds fluoride 100 times stronger than that of the receptor L and L¹ has almost similar efficiency in binding towards acetate ion (AcO^-). The strength of the receptor L¹ towards fluoride, cyanide, acetate and dihydrogen phosphate bindings are found to be in the order of 1.271 × 10⁵ M^-1 > 1.245 × 10⁵ M^-1 > 1.368 × 10³ M^-1, 1.23 × 10³ M^-1 respectively. When we used aqueous environment (10% of water in acetonitrile) as testing solvent system, the receptor L¹ selectively sense cyanide ion. Over all, strength of the receptor is increased towards anions with an increasing the number of fluorine atom onto the receptors. Here in we have also prepared a reference compound L² in which the receptor molecule is substituted with only one fluoride atom. The acetonitrile solution of reference receptor L² with help of naked-eye colorimetric experiment and spectrometric ammonium salts of fluoride, cyanide, acetate and bifluoride results sudden color changes from faint-yellow to brown in color. Unlike receptor L¹, receptor L² does not recognize H₂PO₄^-, but instead of H₂PO₄^-, it recognizes bifluoride as evidenced from UV-Vis spectroscopic and naked-eye colorimetric studies.

Roles of Water Molecules and Counterion on HS- Sensing Reaction Utilizing a Pyrylium Derivative: A Computational Study

In this paper, we present a comprehensive computational study on the hydrogen sulfide ion (HS^-) sensing mechanism in aqueous solution using pyrylium-thiopyrylium transformation. Explicit water molecules up to three water molecules are considered using supramolecular models. The effect of water bulk solvent is also taken into account according to the polarizable continuum model. Our results demonstrate that water molecules are directly involved in the sensing reactions by altering reaction mechanisms and dramatically lower the activation energies. The most favorable HS^- sensing mechanism involves a 10-membered ring transition structure formed by three water molecules and one hydronium. The catalytic effects of water molecule(s) due to the alleviation of ring strain and the stabilization from deprotonated hydronium significantly lower the activation energy. The activation energies in aqueous solution decrease from 40.2 kcal/mol for the hydronium-only-catalyzed reaction to 15.7, 14.8, and 7.4 kcal/mol for one-water-, two-water-, and three-water-catalyzed mechanisms, respectively. In addition, the effect of the counterion tetrafluoroborate (BF₄^-) on the reaction mechanisms was also investigated. Our results demonstrate that the counterion BF₄^- most likely behaves as a spectator and has minor influence on the reaction mechanism.

Simple and highly electron deficient Schiff-base host for anions: First turn-on colorimetric bifluoride sensor

Here in, we have designed, synthesized and isolated sensor L, as a turn-on colorimetric chemo sensor for bifluoride ion. The acetonitrile solution contains L with tetrabutyl ammonium salts of bifluoride, cyanide and fluoride results sudden color changes from yellow to dark brown where as there is no color change observed with any other anionic guests with L. Solution state binding studies of L are carried out by UV-Vis spectrometry titration and the strengths of the chemosensor L towards bifluoride, cyanide and fluoride bindings are found to be 2.67 × 10⁵ M^-1, 4.78 × 10⁵ M^-1_, 4.45 × 10⁵ M^-1 respectively. The strength and sensitivity of the absorbance based assay with L for bifluoride ion, are found to be 2.67 × 10⁵ M^-1 and 0.7 μM respectively, which is the best (highest binding constant and lowest LOD) ever reported in the literature. In order to use this sensor in practical application, we also prepared a cassette which is fabricated with sensor L and we succeeded to sense bifluoride ion.

Molecular Engineering of Free-Base Porphyrins as Ligands-The N-H⋅⋅⋅X Binding Motif in Tetrapyrroles

The core N-H units of planar porphyrins are often inaccessible to forming hydrogen-bonding complexes with acceptor molecules. This is due to the fact that the amine moieties are "shielded" by the macrocyclic system, impeding the formation of intermolecular H-bonds. However, methods exist to modulate the tetrapyrrole conformations and to reshape the vector of N-H orientation outwards, thus increasing their availability and reactivity. Strategies include the use of porpho(di)methenes and phlorins (calixphyrins), as well as saddle-distorted porphyrins. The former form cavities due to interruption of the aromatic system. The latter are highly basic systems and capable of binding anions and neutral molecules via N-H⋅⋅⋅X-type H-bonds. This Review discusses the role of porphyrin(oid) ligands in various coordination-type complexes, means to access the core for hydrogen bonding, the concept of conformational control, and emerging applications, such as organocatalysis and sensors.

Synthesis and anion recognition studies of new oligomethylene bis(nitrophenylureylbenzamide) receptors

A new series of oligomethylene bis(nitrophenylureylbenzamide) receptors were synthesized varying the relative position of the urea and amide groups (ortho4 and meta8) and the length of the oligomethylene chain (C₂ to C₈). An anion recognition study was performed with TBAX salts (X = AcO⁻, BzO⁻, F⁻, H₂PO₄⁻, and HP₂O₇³⁻) by UV-vis and ¹H NMR. The flexibility of these receptors allows a cooperative effect of both ureylbenzamide units in the receptors. Noteworthy, the ortho position favored the 1 : 1 stoichiometry in the complexes with the carboxylates. The formation of 2 : 1 receptor–anion complexes with both types of receptors 4 and 8 and with hydrogen pyrophosphate and high log K values obtained were very significant in this work. The NMR studies evidenced the formation of supramolecular complexes, even in a competitive solvent, such as DMSO.

Synthesis and supramolecular interaction of new oligomethylene bis(4-nitrophenylureylbenzamide) receptors with different anions.

Native Quercetin as a Chloride Receptor in an Organic Solvent

The binding properties of quercetin toward chloride anions were investigated by means of 1H-NMR, 13C-NMR, and electrospray ionization mass spectrometry (ESI-MS) measurements, as well as computational calculations. The results indicate that quercetin behaves primarily as a ditopic receptor with the binding site of the B ring that exhibits stronger chloride affinity compared to the A ring. However, these sites are stronger receptors than those of catechol and resorcinol because of their conjugation with the carbonyl group located on the C ring. The 1:1 and 1:2 complexation of this flavonoid with Cl− was also supported by ESI mass spectrometry.

A concise treatment of pterins: some recent synthetic and methodology aspects and their applications in molecular sensors

A concise account of pterins in chemistry and biology and their applications in molecular sensors including their optical spectroscopic properties are described. Different natural, synthetic, biological and photophysical aspects are also discussed. Synthetic access to direct functionalised pterins and a recently reported new thiophene annulation technique are described for the synthesis of Form B of molybdenum cofactor. The receptor properties of fluorescent pterin molecules including selenopyrimidines which are rarely reported for their binding of anions and neutral molecules are also of major importance in this review. For such an old and still so young, unexplored pterin system on its power to be sensitive for physical studies especially the interaction with cations, anions and neutral molecules are fascinating and research in this area is relatively new and expected to increase fast. Pterin based receptors are for the first time put into a useful review for the advantage of those who want to explore pterin and modified pterin as chromogenic and fluorogenic sensors.

Highly selective recognition of Al3+ and I- ions using a bi-functional fluorescent probe

A tripodal fluorescent probe L1 armed with Rhodamine B and 1-naphthaleneisothiocyanates was prepared in high yield. A study of the recognition properties revealed that probe L1 exhibited high sensitivity and selectivity towards Al³⁺ through a "FRET" fluorescence response and colorimetric response with low detection limits of the order of 10^-8 M. Meanwhile, probe L1 also possessed high recognition ability for I^- through fluorescence decay, which given there are comparatively few selective fluorescent probes for I^-, is significant. Furthermore, the complexation mechanisms were fully investigated by spectral titrations, ¹H NMR spectroscopic titrations and mass spectrometry. The utility of probe L1 as a biosensor in living cells (PC3 cells) towards Al³⁺ ions has also been demonstrated.

Probing the hydrolytic reactivity of 2-difluoromethyl pyrroles

α-Difluoromethyl pyrroles were found to be stable while N-protected with an electron-withdrawing group. Due to the propensity of pyrroles to access azafulvenium-like intermediates, the C-F bonds of an α-difluoromethyl substituent are labile under hydrolytic conditions. The presence of certain electron-withdrawing substituents about the pyrrolic ring can accelerate this process, as determined through a kinetic comparison of the deprotection and subsequent hydrolysis reactions of N-protected β-aryl α-difluoromethyl pyrroles.

Excited state proton transfer (ESIPT) based molecular probe to sense F− and CN− anions through a fluorescence “turn-on” response

Dual anion sensing through an efficient thiazole based phenolic Schiff base containing molecular probe by means of fluorescence “turn-on” response.

Anion-coordination-directed self-assemblies

This review introduces the interplay of anion coordination and supramolecular self-assembly, presenting recent progress in anion-induced and anion-coordination-based self-assemblies.

Miranda M, Busschaert N, Howe ENW, Clarke HJ, Haynes CJE, Kirby IL, Rodilla AM, Pérez-Tomás R, Gale PA, Félix V. Full elucidation of the transmembrane anion transport mechanism of squaramides using in silico investigations

The anion carrier mechanism promoted by squaramide-based molecules has been elucidated by molecular dynamics and chloride efflux studies.

Optical Sensing of Anions via Supramolecular Recognition with Biimidazole Complexes

Phosphorescent metal complexes with peripheral N-H donor functionalities have attracted great attention as potential molecular sensing units for anionic species lately. In this contribution we discuss the development and potential of anion recognition and sensing features of recent examples of luminescent 2,2'-biimidazole complexes of ruthenium(II), iridium(III), osmium(II) and cobalt(III). The general dependency of photophysical features in these complexes regarding the acid-base chemistry of the peripheral N-H functionalities will be outlined as a basic requirement for optical ion recognition. Systematic strategies for the tuning and specific improvement by synthetic means will be discussed regarding recent reports. With respect to their distinct photophysical features, different transition metals are considered individually to demonstrate particular trends regarding ligand modification within the respective groups. In summary, this review elucidates the current state-of-the-art and future potential of the versatile class of 2,2'-biimidazole based sensor chromophores.

p-tert-Butylthiacalix[4]arenes functionalized by N-(4'-nitrophenyl)acetamide and N,N-diethylacetamide fragments: synthesis and binding of anionic guests

New p-tert-butylthiacalix[4]arenes, which are mono-, 1,2-di- and tetrasubstituted at the lower rim containing N-(4'-nitrophenyl)acetamide and N,N-diethylacetamide groups in cone and partial cone conformations have been synthesized. Their complexation ability towards a number of tetrabutylammonium salts n-Bu₄NX (X = F^-, Cl^-, Br^-, I^-, CH₃CO₂^-, H₂PO₄^-, NO₃^-) was studied by UV spectroscopy. The effective receptor for the anions studied as well as selective receptors for F^-, CH₃CO₂^- and H₂PO₄^- ions, which based on the synthesized thiacalix[4]arenes, have been obtained. It was shown that p-tert-butylthiacalix[4]arene tetrasubstituted at the lower rim by N-(4'-nitrophenyl)acetamide moieties bonded to the anions studied with association constants within the range of 3.55 × 10³-7.94 × 10⁵ M^-1. Besides, the binding selectivity for F^-, Cl^-, CH₃CO₂^-, and H₂PO₄^- anions against other anions was in the range of 4.1-223.9. Substituting one or two fragments in the macrocycle with N,N-diethylacetamide groups significantly reduces the complexation ability of the receptor. In contrast to the 1,3-disubstituted macrocycle containing two N-(4'-nitrophenyl)acetamide moieties, the 1,2-disubstituted thiacalix[4]arene, which contains only one such fragment and a N,N-diethylacetamide moiety, selectively binds F^- anions.

Multi-ion detection and molecular switching behaviour of reversible dual fluorescent sensor

The selective chemosensing behaviour of imidazole bisthiocarbohydrazone (IBTC) towards F^- and Cu²⁺ are studied via colorimetric, UV-Visible, fluorescence spectra studies, and binding constants were calculated. The ¹H NMR titration study strongly support that the deprotonation of IBTC followed by the hydrogen bond formation via N1H1 and N2H2 protons with fluoride ion. The fluorescence inactive IBTC-Cu complex became fluorescence active in the presence of perchlorate (ClO₄^-) ion. The selective detection of perchlorate ion was also explained. The F^- sensing mechanism of IBTC has been investigated by Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) methods. The theoretical outcomes well reproduce the experimental results. And it concluded the NH protons, nearby the imine group was first captured by the added F^- ion and then deprotonation happened followed by the formation of hydrogen bond. The IBTC found good reversibility character with the alternative addition of Ca²⁺ and F^-. The multi-ion detection of IBTC was used to construct the NOR, OR and INHIBITION molecular logic gates.