Pyrene Fluorophore Research Articles

Fluorescence and visual sensing of nitroaromatic explosives using electron rich discrete fluorophores

Several π-electron rich fluorescent aromatic compounds containing trimethylsilylethynyl functionality have been synthesized by employing Sonogashira coupling reaction and they were characterized fully by NMR (1H, 13C)/IR spectroscopy. Incorporation of bulky trimethylsilylethynyl groups on the peripheral of the fluorophores prevents self-quenching of the initial intensity through π–π interaction and thereby maintains the spectroscopic stability in solution. These compounds showed fluorescence behavior in chloroform solution and were used as selective fluorescence sensors for the detection of electron deficient nitroaromatics. All these fluorophores showed the largest quenching response with high selectivity for nitroaromatics among the various electron deficient aromatic compounds tested. Quantitative analysis of the fluorescence titration profile of 9,10-bis(trimethylsilylethynyl)anthracene with picric acid provided evidence that this particular fluorophore detects picric acid even at ppb level. A sharp visual detection of 2,4,6-trinitrotoluene was observed upon subjecting 1,3,6,8-tetrakis(trimethylsilylethynyl)pyrene fluorophore to increasing quantities of 2,4,6-trinitrotoluene in chloroform. Furthermore, thin film of the fluorophores was made by spin coating of a solution of 1.0 × 10−3 M in chloroform or dichloromethane on a quartz plate and was used for the detection of vapors of nitroaromatics at room temperature. The vapor-phase sensing experiments suggested that the sensing process is reproducible and quite selective for nitroaromatic compounds. Selective fluorescence quenching response including a sharp visual color change for nitroaromatics makes these fluorophores as promising fluorescence sensory materials for nitroaromatic compounds (NAC) with a detection limit of even ppb level as judged with picric acid.

1,3-Alternate Calix[4]arene Bifuntional Fluorescent Receptor Containing Urea and Crown Ether Moieties

Scheme 1. Synthetic routes to fluorescent chemosensor 1 Calix[4]arenes are important building blocks in supramolecular chemistry. The calixarene framework provides a unique possibility to organize several binding sites in an array complementary to a potential guest. A variety of calixarene-based receptors for cations, anions and neutral molecules have been synthesized in the past decade. Though anion recognition appears to be a relatively new area of research, both positively charged and neutral receptors for anionic species have been prepared in the last few years. As fluorogenic units, pyrenes are one of the most useful because of their relatively efficient excimer formation and emission. Since the intensity ratio of the excimer to the monomer emission (IE/IM) is sensitive to conformational changes of the pyrene-appended receptors, changes in IE/IM upon metal ion complexation can be an informative parameter in various sensing systems. The simultaneous binding of cationic and anionic guest species by ditopic receptors is a rapidly developing new field for ion pair recognition of environment and biological importance. By taking advantage of calixarene framework, a few neutral bifunctional receptors were developed and showed the simultaneous complexation properties of hydrophilic anions and cations in organic media. Those receptors are, however, only focused on the cone conformers of calix[4]arene. It has been known that 1,3-alternate conformation of calix[4]arene could provide the two excellent binding sites for guest molecules when the proper functionalization could be achieved. We have previously reported 'bifunctional calix[4]arene receptors' containing two urea groups and crown ether moieties at the calix[4]arene fixed in the 1,3-alternate conformation. It was shown the simultaneous binding properties of cation and anion guests with enhanced binding affinity of halide anions in the presence of potassium cation. Here we report a new bifunctional receptor 1 based on 1,3alternate conformer of calix[4]arene, which contains urea linking pyrene fluorophores instead of phenylurea and crown ether moieties at the opposite side of lower rim of calix[4]arene fixed in the 1,3-alternate conformation. Also, we studied binding affinity of various anions in the present of potassium ion.

Pyrene Excimer-Based Calix[4]arene FRET Chemosensor for Mercury(II)

A novel calix[4]arene derivative locked in the 1,3-alternate conformation (2) bearing two pyrene and rhodamine fluorophores was synthesized as a selective sensor for the Hg(2+) ion. The sensoring is based on FRET from pyrene excimer emissions to ring-opened rhodamine absorption upon complexation of the Hg(2+) ion. Addition of Hg(2+) to a mixed solution of 2 gave significantly enhanced fluorescence at ∼576 nm via FRET with excitation at 343 nm. We also found that the pyrene excimer emissions formed by the intramolecular π-π interactions are more effective in obtaining strong FRET bands than those by intermolecular π-π interactions.

Probing the Molecular Interactions at the Conducting Polyaniline Nanomaterial Surface via a Pyrene Fluorophore

We report a unique fluorophore cumulant dopant approach for tracing the molecular interaction at the polyaniline nanomaterial surface. Emulsion polymerization of aniline + pyrene sulfonic acid (PSA) produced well-defined fluorescent polyaniline nanofibres of 250 nm diameters with lengths up to 1−3 μM. Post-polymerization doping of a polyaniline emerldine base with PSA produced fluorescent agglomerated nanospheres of 500−700 nm in diameter. Dynamic light scattering (DLS) analysis of the aniline + PSA complex confirmed the existence of ∼25 nm micellar aggregates in the emulsion which templates for the polyaniline nanofibers during the chemical oxidation process. The compositions of the dopant and polymer in the nanomaterials were determined by absorbance spectroscopy. The plots of incorporation of PSA in the nanomaterials versus feed revealed that the dopants incorporated a five times higher amount in the emulsion route compared to that of post-doping process. Wide angle X-ray diffraction (WXRD) analysis sh...

Multicomponent polymeric micelles based on polyaspartamide as tunable fluorescent pH-window biosensors

PHEA-PEG 5000-C 16 is a polyaspartamide polymer with appended hydrophilic PEG 5000 functions and hydrophobic n-C 16 units forming biocompatible micelles with a CAC as low as 1.8 × 10 −7 M. The protonation and acidity constants of the polymer's amino and carboxylic groups have been determined by potentiometric titrations at five different concentrations higher than CAC, finding concentration-independent values. Viscosity and polarity of the micellar core have been investigated by means of fluorescent probes, finding local values comparable to those of pure toluene and to the core of sodium dodecyl sulphate micelles, independently on the protonation degree of the polymer. The fluorophore pyrene, the lipophilic N,N′-dimethyl-N″-dodecylamine and 2-dodecylpyridine self-assemble in the hydrophobic core of PHEA-PEG 5000-C 16 micelles originating a micellar device that behaves as a rare “off-on-off” fluorescence sensor for pH windows, with no interference by the amino and carboxylic functions of the polymer. The “on” state of the sensor includes the physiological 6–8 pH interval, and can be finely shifted in both directions of the pH axis by comicellization of charged cosurfactants. Dialysis experiments demonstrate that the micellar device exibits an efficient retention ability of all molecular components, including cosurfactants, thus candidating for in vivo use.

Pyrene Fluorescence Analysis Offers New Insights into the Conformation of the Lipoprotein-Binding Domain of Human Apolipoprotein E

The C-terminal domain (CT) of apolipoprotein E (apoE), a critical protein involved in cholesterol transport in the plasma and brain, plays an important role in high-affinity lipoprotein binding. Although high-resolution structural information is available for the N-terminal domain of apoE, the structural organization of the CT (residues 201-299) is largely unknown. In this study, we employ site-specific fluorescence labeling with pyrene maleimide to gain insight into the structure and conformation of apoE CT in its naturally self-associated state in buffer at physiologically relevant concentrations (5-50 microg/mL). Pyrene is a highly sensitive fluorophore that reports on spatial proximity between desired sites by displaying unique spectral features. Pyrene was covalently attached to single cysteine-containing recombinant human apoE CT at position 223 or 255 to probe the first predicted helical segment and at position 277 to monitor the terminal predicted helical segment. Regardless of the location of the probe, all three pyrene-labeled apoE CT variants display an intense and dramatic fluorescence excimer band at 460 nm, a signature feature of pyrene, which indicates that two pyrene moieties are within 10 A of each other. In addition, an intense peak at 387 nm (indicative of a highly hydrophobic environment) was noted in all cases. Fluorescence emission quenching by potassium iodide indicates that the accessibility to the probes was restricted at these locations. The possibility that the hydrophobicity of the pyrene moiety was the driving force for helix-helix interaction was excluded because pyrene located at position 209, which is predicted to be located in a nonhelical segment, did not display the above intense unique features. Lastly, denaturation studies suggest that the terminal helix unfolds prior to the first predicted helix in apoE CT. Our studies indicate that there are extensive intermolecular helix-helix contacts throughout the entire CT in the lipid-free state with two apoE CT molecules oriented parallel to each other to form a dimer, which dimerizes further to yield a tetramer. Such an organization allows helix-helix interactions to be replaced by helix-lipid interactions upon encountering a lipoprotein surface, with the terminal helix likely initiating the binding interaction. This study presents the possibility of employing pyrene fluorophores as powerful new alternatives to obtain conformational information of proteins at physiologically relevant concentrations.

Novel interstrand communication systems within DNA duplexes based on 1-, 2- and 4-(phenylethynyl)pyrenes attached to 2′-amino-LNA: high-affinity hybridization and fluorescence sensing

Functionalisation of 2'-amino-LNA oligonucleotides with 1-, 2- and 4-(phenylethynyl)pyrene fluorophores via a carbonyl linker (PEPyc) resulted in efficient interstrand communication systems in nucleic acid duplexes, providing effective tools for stabilization of nanostructures and fluorescence monitoring of DNA self-assembly.

Boronic acid based photoinduced electron transfer (PET) fluorescence sensors for saccharides

A simple three step synthesis was developed to provide six novel modular sensors, consisting of three para sensors, and three meta sensors with naphthalene, anthracene and pyrene fluorophores. The interaction of the six sensors with the saccharides: D-glucose, D-fructose, D-galactose, and D-mannose, were evaluated. All sensors displayed increasing fluorescence intensity upon the addition of these saccharides, with all of the sensors showing enhanced selectivity for D-glucose over D-galactose, D-fructose and D-mannose. High affinity (Kobs) was also observed for the meta sensors with respect to the para sensors. The naphthalene and anthracene meta sensors showed particularly high affinity (Kobs) for D-galactose. Circular dichroism spectroscopy was used to probe the structures of the complexes formed. Cyclic complexes were formed between all six sensors and D-glucose. Whilst naphthalene and anthracene meta sensors which displayed high affinity for D-galactose also formed cyclic complexes with that saccharide.

Tuning the Intramolecular Charge Transfer of Alkynylpyrenes: Effect on Photophysical Properties and Its Application in Design of OFF−ON Fluorescent Thiol Probes

Green and yellow-emitting 1,6- and 1,8-bis(phenylethynyl) pyrenes (dyes 7, 8, 9, and 10) with different intramolecular charge transfer (ICT) feature were synthesized and the effect of ICT on the photophysical properties of these derivatives were studied by UV-vis absorption spectra, fluorescence emission spectra, and DFT/TDDFT calculations. For the dyes with electron-pushing group (e.g., -dimethylamino, dye 8 and dye 10), structureless and solvent polarity-sensitive fluorescence emission spectra were observed. Conversely, dye with electron-withdrawing group (e.g., -CN, dye 7) shows structured and solvent polarity-independent emission spectra. OFF-ON fluorescent thiol probes 11 and 12 with 2,4-dinitrobenzenesulfonyl protected ethynylpyrene fluorophore were designed based on DFT/TDDFT calculations, which predicts dark state (S(1)) for these thiol probes (e.g., oscillator strength f = 0.0086 for S(1)<--S(0) transition of the probe 11). This dark state is induced by the ICT effect with ethynylated pyrene fluorophore as electron donor and 2,4-dinitrobenzenesulfonyl unit as electron acceptor. Cleavage of the 2,4-dinitrobenzenesulfonyl unit by thiol releases the free fluorophore, for which the lowest-lying excited state S(1) is no longer a dark state, but an emissive state (f = 0.9776 for S(1)<--S(0) transition). These theoretical predictions on the photophysical properties of the molecular probes were fully proved by experimental results. Our results demonstrated that the fluorescence OFF-ON switching of this kind of thiol probe is due to the termination of the ICT effect (which quenches the emission, by a dark S(1) state) by cleavage of the 2,4-dinitrobenzenesulfonyl unit (as acceptor of ICT effect) with thiols, not the re-establishment of the D-pi-A feature of the fluorophore. These investigation on the pyrene derived green-emitting fluorophores and the DFT/TDDFT calculation aided probe design suggest that future application of these results may prove useful toward the rational design of fluorophores or fluorescent probes with predetermined photophysical properties.

Synthesis of novel bispyrene diamines and their application as ratiometric fluorescent probes for detection of DNA

Fluorescent DNA probes with 1,6-hexanediyl as the linker between two pyrenes, phenylpyrenes or phenylethynyl pyrene fluorophores were synthesized ( Py-1, Py-2 and Py-3) and their interactions with DNA were studied by UV–vis absorption spectra, fluorescence spectra and viscosity measurements. The probes show red-shifted emission compared with pyrene (up to 20 nm). We found the interaction of these probes with DNA can be either intercalation or groove binding. Ratiometric fluorometry (ratio of the monomer and excimer emission intensity versus concentration of DNA) was achieved with these probes for DNA quantification (with limit of detection, LOD, up to 0.1 μg/mL). We also found that the undesired oxygen sensitivity of the emission intensity of pyrene fluorophore can be greatly suppressed by extending the π-conjugation framework of pyrene (the I Ar/ I air value is decreased from 8.10 for pyrene to less than 2.20 for the DNA probes described herein).

Highly selective fluorescent chemosensor for Na+ based on pyrene-modified calix[4]arene derivative

A novel calix[4]arene derivative with pyrene fluorophores at the upper rim and tetraester ionophores at the lower rim was synthesized in six steps, and its structure was proved by NMR and ESI-MS spectroscopies. Furthermore, the chemosensing behavior of the host compound for alkali and alkaline earth metal ions was investigated by fluorescence spectroscopy. The obtained results show that the calixarene host can selectively bind sodium ion with the complexation stability constant of 2190 mol−1·L. The complexation with sodium ion can pronouncedly induce the excimer emission to decrease and the monomer emission to increase, whereas the addition of the other alkali and alkaline earth metal ions does not cause appreciable changes in the fluorescence spectrum of the host compound. The present calix[4]arene derivative displays potential application as fluorescent chemosensor for sodium ion.

Membrane Fluidity and Surface Changes During Initiation of 1,2 Dimethylhydrazine-Induced Colon Carcinogenesis: Protection by Zinc

The present study evaluated the modulatory effects of zinc on colonic membrane fluidity and surface abnormalities following 1,2 dimethylhydrazine (DMH)-induced colon carcinogenesis. Rats were segregated into four groups: normal control, DMH treated, zinc treated, DMH + zinc treated. Colon carcinogenesis was initiated through weekly subcutaneous injections of DMH (30 mg/kg body weight) for 8 weeks. Zinc (in the form of zinc sulphate) was supplemented to rats at a dose level of 227 mg/L in drinking water, ad libitum, for the entire duration of the study. Brush border membranes (BBM) were isolated from the colon of rats and the fluidity parameters were assessed by steady-state fluorescence polarization technique using the membrane extrinsic fluorophore 1,6-diphenyl-1,3,5-hexatriene (DPH). The translational diffusion was measured by using the excimer formation of pyrene incorporated in the membrane. The results demonstrated a significant increase in the polarization and anisotropy, accompanied by an increase in order parameter in the membrane preparations from the colon of DMH-injected rats. Further, studies with pyrene fluorophore indicated a marked decrease in membrane microviscosity following DMH treatment. However, the alterations in membrane fluorescence polarization and the fluidity parameters were completely restored following zinc treatment. Drastic alterations in colon surface were noticed after 8 weeks of DMH treatment. However, zinc treatment to DMH-treated rats greatly restored normalcy in the colonic surface. The study concludes that zinc has a strong membrane stabilizing effect and thus has a positive beneficial effect against chemically induced colonic preneoplastic progression in rats.

Photoinduced electron transfer and surface plasmon resonance in materials consisting of pyrene fluorophore and Au nanorods immobilized on MCM-48 surface

Mesoporous silica of the MCM-48 type as a support for fluorophore molecules was functionalized with 3-aminopropyl and 3-thiolopropyl groups. Then, molecules consisting of a fluorophore pyrene group and receptor fragments with donor N and O atoms were covalently attached by grafting of carboxyl groups to amino groups on a mesoporous silica surface. Additionally, Au nanorods were attached to thiol groups on the same surface. The vicinity of Au nanorods in a material with pyrene derivatives covalently grafted on the functionalized MCM-48 silica enhanced fluorescence of the composite material due to the surface plasmon resonance effect. The fluorescence emission of the prepared recognition material is quenched specifically owing to the photoinduced electron transfer effect after coordination reactions with Cu(II) ions. Moreover, the material exhibits selectivity for Cu(II) cations in aqueous solutions in presence of such metal ions as: alkali, alkaline earth, transition and heavy metals. During UV irradiation the studied material undergoes slowly photochemical degradation as a potential recognition element.

Multiparametric Fluorescence Detection of Early Stages in the Amyloid Protein Aggregation of Pyrene-labeled α-Synuclein

The aggregation of α-synuclein, a presynaptic protein, has an important role in the etiology of Parkinson’s disease. Oligomers or protofibrils adopting the cross-β-sheet structure characteristic of fibrillating amyloid proteins are presumed to be the primary cytotoxic species. Current techniques for monitoring the kinetics of α-synuclein aggregation based on fluorescent dyes such as Thioflavin-T and Congo red detect only the terminal fibrillar species, are discontinuous and notoriously irreproducible. We have devised a new fluorescence aggregation assay that is continuous and provides a large set of fluorescence parameters sensitive to the presence of oligomeric intermediates as well as fibrils. The approach involves tagging functionally neutral Ala-to-Cys variants of α-synuclein with the long-lifetime fluorophore pyrene. Upon induction of aggregation at 37 °C, the entire family of steady-state descriptors of pyrene emission (monomer intensity, solvent polarity ratio (I I /I III ), and anisotropy; and excimer intensity) change dramatically, particularly during the early stages in which oligomeric intermediates form and evolve. The pyrene probe senses a progressive decrease in polarity, an increase in molecular mass and close intermolecular association in a manner dependent on position in the sequence and the presence of point mutations. The time-resolved decays (0–160 ns) of intensity and anisotropy exhibited complex, characteristic features. The new assay constitutes a convenient platform for the high-throughput screening of agents useful in the diagnosis and therapy of Parkinson’s disease as well as in basic investigations.

Convenient synthesis of macrocycles with catechol-type moiety and their neutral boron complexes with pyrene fluorophore for anion sensing

A series of medium ring-sized macrocycles 4a–4e bearing catechol-type moiety were synthesized readily by direct cyclization of di(acid chloride) 1 with diamine derivatives without high-dilution conditions followed by tandem Claisen rearrangement. Complexation of macrocycles 4 with 1-pyrene-boronic acid yielded their corresponding neutral macrocyclic boron complexes 5 with pyrene unit as fluorophore in high yields. Anion sensing properties of these neutral boron complexes were also investigated.

DNA Duplex-Based Fluorescence Probes/Sensors Using Monomer-Excimer Switching

In this review, we report DNA duplex-based fluorescence probes/sensors using pyrene monomer-excimer switching. The review mainly comprises two topics: 1) excimer-monomer switching molecular beacons (EMS-MB) and 2) monomer-excimer switching sensors based on the structural motif of antibodies. The EMS-MBs have two pyrene fluorophores connected both at 3' and 5' ends of a single-stranded oligonucleotide. Emission switching occurs from excimer to monomer accompanying isoemissive points when the probes hybridized with target DNAs. The isoemissive points indicate the presence of only two fluorescent species, nonhybridized and hybridized probes in the mixtures, and thereby unambiguous detection of the targets is available. The probes can detect target 19-mer DNAs and can discriminate the targets from their single-nucleotide mismatches at 1 nM concentration. Furthermore, the EMS-MBs have been recently applied to kinetic study for RNase H activity by Tan et al. The structures and emission-switching properties of the EMS-MBs encourage us to develop a new class of fluorescent sensors based on the structural motif of antibodies. The sensors consist of three functional regions, benzo-15-crown-5 ether (or per-O-methylated beta-cyclodextrin), DNA, and pyrene as guest-binding, dimerizing, and sensing sites, respectively. The crown- and CD-modified sensors can detect potassium cation and porphyrin derivatives, respectively, by monomer-excimer emission switching.

Changes of the Membrane Lipid Organization Characterized by Means of a New Cholesterol-Pyrene Probe

We synthesized 3 β-hydroxy-pregn-5-ene-21-(1-methylpyrenyl)-20-methylidene (Py-met-chol), consisting of cholesterol steroid rings connected to a pyrene group via a linker without polar atoms. This compound has interesting spectroscopic properties when probing membranes: 1), The pyrene has hypochromic properties resulting from probe self-association processes in membranes. Using liposomes of various lipid compositions, we determined the association constants of the probe ( K): K DOPC ≫ K POPC ≫ K DMPC > K DMPC/15 mol % Chol > K DMPC/30 mol % Chol . This indicates a better probe solvation in saturated than in unsaturated lipids, and this effect is enhanced as the cholesterol concentration increases. 2), The pyrene fluorophore is characterized by monomer ( I 1– I 5) and excimer ( I E) emission bands. In model membranes, I 1/ I 3 and I E/ I 3 ratios revealed a correlation between the polarity of the lipid core of the membrane and the amount of cholesterol. 3), Using this probe, we monitored the first steps of the signaling pathway of the mouse δ-opioid receptor, a G-protein-coupled receptor. The thickness of the membrane around this receptor is known to change after agonist binding. Fluorescence spectra of living Chinese hamster ovary cells overexpressing mouse δ-opioid receptor specifically revealed the agonist binding. These results indicate that Py-met-chol may be useful for screening ligands of this family of receptors.

A New Pyrene-Based Fluorescent Probe for the Determination of Critical Micelle Concentrations

A new pyrene-based fluorescent probe for the determination of critical micelle concentrations (CMC) is described. The title compound 1 is obtained in five steps, starting from pyrene. Fluorescence spectroscopic properties of 1 are studied in homogeneous organic solvents and aqueous micellar solutions. In a wide range of organic solvents, probe 1 exhibits a characteristic monomer emission of the pyrene fluorophore, with three distinct peak maxima at 382, 404, and 425 nm. The spectra change dramatically in aqueous solution, where no monomer emission of the pyrene fluorophore is detected. Instead, only strong excimer fluorescence with a broad, red-shifted emission band at lambda(max) = 465 nm is observed. In micellar aqueous solution, a superposition of the monomer and excimer emission is found. The appearance of the monomer emission in micellar solution can be explained on the basis of solubilization of 1 by the surfactant micelles. The ratio of the monomer to excimer fluorescence intensities of 1 is highly sensitive to changes in surfactant concentration. This renders 1 a versatile and sensitive probe molecule for studying the micellization of ionic and nonionic surfactants. For a representative selection of common surfactants, the critical micelle concentrations in aqueous solution are determined, showing excellent agreement with established literature data.

Self-Duplex Formation of an APy-Substituted Oligodeoxyadenylate and Its Unique Fluorescence

Unexpected homoadenine self-duplexes are formed when pyrene units are bound covalently to the deoxyadenosine bases at specific distances (1,4 relationships). This discovery illustrates how small-molecule pyrene intercalators can be used to drive unknown nucleic acid assembly with a concomitant change in fluorescence. When a pair of pyrene fluorophore units is located within an oligodeoxyadenylate chain, the system can display three different colors (reddish-orange, green, or blue) depending on the relative location of the fluorophores. A unique fluorescence signal, a reddish band peaking at 580 nm, appears when the oligomers possess more than two spacers between the pyrene fluorophores(1,4 relationships). Several spectroscopic experiments, for example, recording variable-concentration spectra, CD, UV, melting temperature, and gel electropherogram, indicate that this new reddish band came from an intermolecular homoadenine self-duplex. Time-resolved fluorescence measurements using both TCSPC and upconversion methods indicate that this unique fluorescence has a long lifetime.

Cyclams Bearing Diametrically Disubstituted Pyrenes as Cu2+- and Hg2+-Selective Fluoroionophores

New cyclam derivatives having diametrically disubstituted pyrene fluorophores were prepared and their fluoroionophoric properties toward transition metal ions were investigated. The compounds exhibited significant selectivity toward Hg2+ and Cu2+ ions in switching-off type responses in aqueous methanol or acetonitrile solution. Dipyrene-diamide derivative 3, having extra binding sites of the amide function, exhibited more pronounced chemosensing behavior toward Hg2+ and Cu2+ ions than its parent, dipyrene derivative 2. Detection limits for the analysis of Hg2+ and Cu2+ ions of dipyrene-diamide derivative 3 were 1.45x10(-6) and 1.30x10(-6) M, respectively. The diametrically disubstituted dipyrene-cyclam 2 may be utilized as a new starting platform for the design of other supramolecular fluorescent signaling systems having switching or chemosensing behaviors toward transition metal ions.