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The sensing ability of benzoporphyrins 1-5 and porphyrin-2-ylpyridines 6-10 towards different metal ions Na+, K+, Ca2+, Mg2+, Pb2+, Cu2+, Ni2+, Zn2+, Cd2+, Hg2+, and Cr3+ was explored in solution by absorption and fluorescence spectroscopy. Strong changes in the ground and excited state were detected only in the case of the soft metal ions Zn2+, Cd2+, Hg2+, and Cu2+. A one metal per ligand molar ratio was obtained in all cases for compounds1-5. In addition, a remarkable increase of the emission intensity for 1-5 was observed in the presence of Hg2+. In this series the highest association constant was obtained for compound1 (logK(ass)=(8.71 +/- 4.81)x10(-3)), which was able to quantify 32ppb of Hg2+. For compounds6-10 containing an additional pyridine unit, a metal-to-ligand stoichiometry of 1:2 was determined. The gas-phase detection abilities of compounds1-10 using MALDI-TOF-MS spectrometry confirmed that their sensorial ability and theoretical calculations are in accordance with the stoichiometry observed. Our preliminary studies show that some of the compounds supported in polymethylmethacrylate (PMMA) films can be used as promising metal-ion solid chemosensors; it was found that compound 1 in PMMA is able to distinguish between Zn2+ and Hg2+ in the solid phase.

This work presents a systematic evaluation of 2-amino, 5-amino and 2,5-diamino substituted benzimidazo[1,2-a]quinoline-6-carbonitriles as novel pH probes with a potential application in pH sensing materials or as H+ fluoroionophores in bulk optode membranes. The study was carried out by varying the length, type and position of amino substituents in ten fluorescent dyes with the same benzimidazo[1,2-a]quinoline-6-carbonitrile core. The photophysical and acid-base properties of the dyes were investigated by the UV/Vis absorption and fluorescence spectroscopies, and interpreted by the electronic structure DFT calculations. pH sensing mechanisms and structure-property relations affecting the fluorescence response were discussed through a detailed analysis of the piperidine substituted derivatives 1–4. Push–pull donor–acceptor interactions stimulate strong fluorescence in the visible spectral range (up to Φ = 0.65 for 7) and induce significant changes in the photophysical properties associated with the acid-base equilibria (up to a 50-fold increase in the fluorescence intensity). pKa values in aqueous and mixed solutions (v/v H2O:EtOH 99:1, 50:50), appear suitable for monitoring acidic pH in solution. The most promising candidates were immobilised in thin polymer matrices by the spin coating technique to form fluorescent sensing materials – optodes, and examined as novel pH-sensitive fluoroionophores. In the liquid membrane environment, dyes exhibited significant increase of the apparent pKas by almost 4 units. Bright and blue emissive thin films showed pH response and dynamic range around pKa = 5, making them suitable for a wide range of optical sensing applications.

We developed an asymmetric fluorescent sensor 1 for Cu2+, based on 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY), by introducing 4-carboxyphenyl and bis(pyridin-2-ylmethyl)amine groups at the 5- and 3-positions, respectively, of the BODIPY core. We then investigated the photophysical and cation-sensing properties of the sensor. BODIPY 1 showed large absorption and fluorescence spectral shifts on binding to Cu2+. The fluorescence peak at 580 nm red-shifted to 620 nm. The binding stoichiometry of BODIPY 1 and Cu2+ was 1:3. The ratio of the fluorescence intensity at 620 nm to that at 580 nm (F620/F580) increased with increasing concentration of Cu2+ (3–10 equiv); this enabled ratiometric determination of Cu2+. Although BODIPY 1 showed good selectivity for Cu2+, there was an interfering effect of Fe3+. BODIPY 1 could be used for the naked-eye detection of Cu2+ in a water-containing sample.

A series of boron dipyrromethene (BODIPY) dyes containing two aldehyde functional groups at the 3 and 5 positions have been synthesized in low-to-decent yields in two steps. In the first step, the meso-aryl dipyrromethanes were treated with POCl(3) in N,N-dimethylformamide to afford 1,9-diformylated dipyrromethanes. In the second step, the diformylated dipyrromethanes were first in situ oxidized with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and then reacted with BF(3)center dot OEt(2) to afford 3,5-diformylboron dipyrromethenes. The X-ray structural analysis indicated that the aldehyde groups are involved in intramolecular hydrogen bonding with fluoride atoms, which may be responsible for the stability of the diformylated BODIPY compounds. The presence of two formyl groups significantly alters the electronic properties, which is clearly evident in downfield shifts in the (1)H and (19)F NMR spectra, bathochromic shifts in the absorption and fluorescence spectra, better quantum yields, and increased lifetimes compared to 3,5-unsubstituted BODIPYs. Furthermore, 3,5-diformylboron dipyrromethenes are highly electron-deficient and undergo facile reductions compared to unsubstituted BODIPYs. These compounds exhibit pH-dependent on/off fluorescence and thus act as fluorescent pH sensors.

Di-derivatives of 1,1'-methylene-bis(2-naphthol) (L(1)) possessing ester (L(2)), carboxylic acid (L(3)) or picolyl (L(4)) as end groups of the pendants have been synthesized and characterized. Titration of these derivatives for their recognition towards M(2+) (where M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn) were performed by following the fluorescence emission intensities in methanol solution. The picolyl derivative (L(4)) has been found to be well suited for Cu(2+) recognition (

Amide linked lower rim 1,3-dibenzimidazole derivative of calix[4]arene, L has been shown to be sensitive and selective to Hg(2+) in aqueous acetonitrile solution based on fluorescence spectroscopy, and the stoichiometry of the complexed species has been found to be 1:1. The selectivity of L toward Hg(2+) has been shown among 11 M(2+) ions, viz., Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), Ca(2+), and Mg(2+) studied, including those of the mercury group and none of these ions impede the recognition of Hg(2+) by L. Role of the solvent on the recognition of Hg(2+) has been demonstrated. The role of calix[4]arene platform and the benzimidazole moieties in the recognition of Hg(2+) by L has been delineated upon performing such studies with five different molecules of relevance as reference molecular systems. The binding cores formed by the receptor L and the reference compounds have been established based on the single crystal XRD structures, and the preferential metal ion binding cores have been discussed. The binding of Hg(2+) with L has been further established based on (1)H and (13)C NMR, ESI MS, absorption, and fluorescence lifetime measurements. Some of these techniques have been used to establish the stoichiometry of the species formed. The complex species formed between L and Hg(2+) have been isolated and characterized and found to be 1:1 species even in the isolated complex. Whereas transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) provided the nanostructural behavior of L, the TEM and SEM demonstrated that the mercury complex has different characteristics when compared to L. The TEM, SEM, and powder XRD studies revealed that whereas L is crystalline, that of the mercury complex is not, perhaps a reason for not being able to obtain single crystals of the complex. Binding characteristics of Hg(2+) toward L have been established based on the DFT computational calculations.

International audience; Two N-pyrenylacetamide-substituted sugar-aza-crown ethers have been synthesized as new fluorescent chemosensors. The designed ligands 1 and 2 exhibit fluorescence characteristics of a pyrene monomer and a dynamic excimer emission when compared to N-pyrenylacetamide as a model compound. Both ligands displayed a Cu2+-sensitive fluorescence quenching with a 1:1 stoichiometry and high stability constants (log K = 6.7 for 1 and 7.8 for 2). The quenching effect was rationalized on the basis of photoinduced electron transfer from the excited pyrene to the complexed Cu2+ cation, while the changes in excimer-to-monomer ratio were explained by a conformational analysis through DFT calculations. The predicted structure suggests that the Cu2+ cation is coordinated with the two carbonyl groups and the sugar-aza-crown ethers which rigidified the complex structure and placed the two pyrene moieties far apart.

A new malonate possessing two pyrene moieties was synthesized as a fluoroionophore, and its structure and fluorescence spectroscopic properties were investigated. When excited at 344 nm in acetonitrile/chloroform (9:1, v/v), the synthesized bispyrenyl malonate has the fluorescence of intramolecular excimer (λem = 467 nm) emissions and not a pyrene monomer emission (λem = 394 nm). A large absolute fluorescence quantum yield was obtained in the solid state (ΦPL = 0.65) rather than in solution (ΦPL = 0.13). X-ray crystallography analysis clarified the molecular structure and alignment of the bispyrenyl malonate in the crystal phase, elucidating its fluorescence spectroscopic properties. Such analysis also suggests there are intramolecular C–H···π interactions and intermolecular π···π interactions between the pyrenyl rings. Interestingly, the synthesized bispyrenyl malonate exhibits excellent fluorescence sensing for the Cu2+ ion. Remarkable fluorescence intensity enhancement was only observed with the addition of the Cu2+ ion.

Fluorescence spectroscopy has great potential for on-site and real-time monitoring of pollutants in aquatic environments; however, its application to environmental aquatic samples has been extremely limited. In this study, a novel fluoroionophore based on a BODIPY-terpyridine conjugate was developed and applied to determine Zn concentrations in urban runoff. The fluoroionophore selectively bound to Zn(2+) in water, which led to an instant red-shift of the fluorescence peak of the fluoroionophore from 539 nm to 567 nm that could be seen by the naked eye. Zn concentrations could be quantified using the ratio of fluorescence intensities, and the detection limit was 9 μg/L, which is sufficiently low for environmental aquatic samples. To demonstrate applicability of the method to environmental samples, we measured Zn concentrations in urban runoff samples with a complex matrix (∼60 mg/L dissolved organic carbon and ∼20 mS/cm electrical conductivity). The total and dissolved fractions of Zn in the samples could be determined by fluorescence spectroscopy and its relative error was estimated to be less than 30% by inductively coupled plasma-atomic emission spectroscopy analysis. The proposed method is rapid and easy-to-use with simple pretreatment for Zn determination in environmental aquatic samples with complex matrices.

Keywords: fluorescence ; metallacrown complexes ; ruthenium ; self-assembly ; sensors ; Supramolecular Triangular Hosts ; Organometallic Receptors ; Selective Extraction ; Crown-Ethers ; Complexes ; Li+ ; Sensor ; Recognition ; Fluoroionophore ; Ionophore Reference EPFL-ARTICLE-148459doi:10.1002/chem.200903119View record in Web of Science Record created on 2010-04-23, modified on 2017-05-12

A new 1,3-di-capped calix[4]arene conjugate of salicylidene (L) has been synthesized, characterized and the structure has been established by single crystal XRD. L shows selectivity towards Hg(2+) in ethanol by turn-on fluorescence among the biologically important metal ions studied. The species of recognition has been modeled by DFT computational calculations to result in conformational changes in the arms that support the turn-on fluorescence behaviour.

Fluorescent dihydroxypyridine ligands were prepared by attaching pyrene-, dansyl-, and methoxycoumarin-fluorophores via dimethyleneamine linkers. The reaction of these ligands with [(p-cymene)RuCl(2)](2) or [(C(6)H(5)CH(2)NMe(2)H)RuCl(2)](2)Cl(2) resulted in the formation of 12-metallacrown-3 complexes, which possess strong affinity for lithium ions. By a judicious choice of the fluorophore and the arene pi-ligand, a macrocycle was obtained that could be used in aqueous solution to selectively and quantitatively detect lithium ions by fluorescence spectroscopy.