Catechol derivatives as fluorescent chemosensors for wide-range pH detection

The synthesis and characterization of a new family of catechol derivatives designed to behave as fluorescent chemosensors for wide-range pH detection has been described. These compounds were prepared by covalently coupling a catechol unit with other aromatic rings, thus obtaining pi-delocalized systems with both pH-responsive groups and fluorescent behavior. In the case of a pyridine-catechol derivative, this leads to up to three different protonation states with distinct optical properties in organic media, as corroborated by density functional theory calculations. By applying dual-wavelength detection techniques, this compound shows complementary "off-on-off" and "on-off-on" emission profiles upon pH variation, a behavior that can be exploited to perform acidity detection over a broad pH range.     

Chiral cyclohexane based fluorescent chemosensors for enantiomeric discrimination of aspartate

Some new chiral cyclohexyl based fluorescent anion receptors have been synthesized and their absolute configuration has been determined by using circular dichroism (CD). Complexation experiments have been carried out with several dicarboxylates, and stoichiometries and complexation constants for the corresponding complexes have been determined. The chiral discrimination ability of these ligands for chiral dicarboxylates has been studied and the best results have been obtained with TMA aspartate.     

静电纺荧光纳米纤维膜在痕量爆炸物检测中的应用

爆炸物检测作为打击爆炸恐怖主义的重要措施之一,正日益彰显出广阔的应用前景.其中,静电纺荧光纳米纤维膜在爆炸物检测领域已展现出其独特的优点,可满足爆炸物检测所需的检测速度快、检测灵敏度高等要求.本文总结了近年来静电纺荧光纳米纤维膜在爆炸物检测中的代表性成果,简要介绍了爆炸物荧光传感机理、静电纺丝技术原理、静电纺荧光纳米纤维膜的制备方法及其爆炸物检测性能的影响因素;系统、重点梳理了有机小分子体系、共轭聚合物体系、聚集诱导发光体系及其他荧光材料体系的静电纺荧光纳米纤维膜在爆炸物检测中的应用,并针对该领域尚未解决的问题和未来可能的发展方向进行了展望,可为实际爆炸物检测中静电纺荧光纳米纤维膜的设计提供指导.     

Self-assembled fluorescent chemosensors

Self-assembling and self-organizing methodologies are powerful tools for the "bottom-up" approach for the realization of complex structure with functional properties. Recently, this concept has been extended to the design of fluorescent chemosensors providing new exciting potentialities for the development of innovative sensing systems. This Concept Article deals mainly with this new approach and discusses its evolution, applications, and limitations.     

Flavonol based ruthenium acetylides as fluorescent chemosensors for lead ions

Flavonol based alkynyl ruthenium complexes devoted to the detection of metal traces in solution are described. The sensitivity of both absorption and emission properties of the 3-hydroxyflavone unit as a receptor for the metal cations, and of an alkynyl ruthenium moiety as an extended π-conjugated system, provides an efficient molecular sensor for rapid, sensitive and selective detection of lead(II) cations.     

Tetraphenylethene based zinc complexes as fluorescent chemosensors for pyrophosphate sensing

We described a serious of zinc complexes that exhibit characteristic fluorescence responses toward pyrophosphate(PPi) and adenosine triphosphate(ATP) in aqueous media. These novel probes exploited tetraphenylethene(TPE) as fluorophore and macrocycle-polyamine(including 1,4,7,10-tetraazacyclododecane and 1,4,7-triazacyclononane) Zn(II) complexes as binding group. These ‘‘OFF–ON' type probes exhibited promising selectivity and sensitivity to PPi and ATP via a restriction of intramolecular rotation(RIR) mechanism. The detection limit for PPi was found within nmol/L range.     

Recent progress in fluorescent and colorimetric chemosensors for detection of amino acids

Due to the biological importance of amino acids, the development of optical probes for these molecules has been an active research area in recent years. This tutorial review focuses on recent contributions since the year 2000 concerning the fluorescent or colorimetric sensors for amino acids, and is organized according to their structural classification and reaction types. For reaction based chemosensors, the works are classified according to the mechanisms between sensors and amino acids, including imine formation, Michael addition, thiazinane or thiazolidine formation, cleavage of a sulfonate ester, cleavage of disulfide, metal complexes-displace coordination and others.     

New fluorescent chemosensors for silver ion

New fluorescent chemosensors, 1,8-bis(pyrazolylmethyl)anthracene and 9,10-bis(pyrazolylmethyl)anthracene, were synthesized. The 1,8-isomer showed selective fluorescent quenching effects with Ag(I) and Cu(II). On the other hand, the 9,10-isomer displayed a selective fluorescent quenching effect only with Ag(I). From the association constants obtained from fluorescent titrations and by extraction, we conclude that rigid immobilization of the ligands, 1,8-isomer, plays a more important role in the binding with Ag(I) than the additional pi-cation interaction offered by the 9,10-isomer.     

New fluorescent and colorimetric chemosensors based on the rhodamine and boronic acid groups for the detection of Hg

Novel rhodamine B (RB) derivatives bearing mono and bis-boronic acid groups were investigated as Hg²⁺ selective fluorescent and colorimetric sensors. These derivatives are first examples of reversible fluorescent chemosensors for Hg²⁺ which utilized boronic acid groups as binding sites. Two new RB-boronic acid derivatives displayed selective ‘Off-On’-type fluorescent enhancements and distinct color changes with Hg²⁺. Selective fluorescent enhancement of two rhodamine derivatives was attributed to ring opening from the spirolactam (nonfluorescent) to ring-opened amide (fluorescent).     

Thiazole-tethered biaryls as fluorescent chemosensors for the selective detection of Fe3+ ions

3-Amino-5-(thiazol-2-yl)-[1,1′-biaryl]-2,4-dicarbonitriles have been synthesized employing a facile one-pot pseudo four-component domino strategy. All these thiazole-tethered biaryls exhibited blue fluorescence under UV lamp. Based on the high relative quantum yield, three compounds namely, 4a , 4d , and 4i , were chosen to explore the metal interference studies. Against several metal ions, these three thiazole-tethered biphenyl probes were found to be effective fluorescent chemosensors for the selective and sensitive detection of Fe³⁺ ions with a lower detection limit of 0.18, 0.12, and 0.16 μM, respectively.     

Highly selective fluorescent chemosensors for cadmium in water

The design, synthesis and photophysical evaluation of two new chemosensors 1 and 2 is described for the selective detection of Cd(II) in water at pH 7.4. Both are based on the use of aromatic iminodiacetate receptors that connected to an anthracene fluorophore by covalent methyl spacers. These are highly water-soluble sensors where the fluorescence is ‘switched off’ between pH 3-11, due to photoinduced electron transfer (PET) quenching of the anthracene excited state by the receptor. Upon protonation of the receptor, the emission was however, ‘switched on’. From these changes pK_as of 1.8 and 2.5 were determined for 1 and 2 respectively. Both showed good selectivity for Cd(II) over competitive ions such as group II and Zn(II), Cu(II), Co(II). For 1, having a single receptor, only a weak monomer anthracene emission was observed for the free sensor at pH 7.4 (HEPES buffer, 135 mM NaCl). Upon Zn(II) titration, a broad red shifted emission occurred, centred at 468 nm. In the presence of Cd(II), a similar red shifted emission was also observed, however, this time centred at 506 nm. In contrast to these results, the fluorescence of 2 in the presence of Zn(II) gave rise to typical monomeric anthracene emission, due to suppression of PET, that is, the anthracene emission was ‘switched on’. Nevertheless, in the presence of Cd(II) a broad emission centred at 500 nm was observed, similar to that seen for 1. These ion induced long wavelength emission bands were assigned to the formation of charge-transfer complexes (exciplexes) between the anthracene moieties and the ion-receptor complexes. Importantly, for both 1 and 2, a selective detection of Cd(II) was possible, even in the presence of Zn(II).     

A fluorescent Cd(II) based 2-D coordination polymer for highly selective detection of nitroaromatics and Hg2+

A 2-D Cd(II) coordination polymer (CP), {[Cd₂(L)₂(4,4′-bipy)₂(H₂O)?7H₂O]_n (1), has been synthesized using 5-aminoisophthalic acid (H₂L) as ligand and 4,4′-bipyridine as co-ligand. A single-crystal X-ray diffraction study shows that 1 is an infinite 2-D layer. CP 1 behaves as a highly selective and sensitive fluorescence chemosensor for detection of Hg²⁺ and 2,4,6-trinitrotoluene (TNT). Furthermore, possible emission quenching in 1 in the presence of nitroaromatics has been addressed with the aid of theoretical calculations. The calculations indicated that there are both electron and energy transfer processes, in addition to electrostatic interaction between 1 and nitroaromatics which contributes to the selective fluorescence quenching.     

Rhodamine urea derivatives as fluorescent chemosensors for Hg

New rhodamine derivatives bearing urea group have been synthesized for the detection of metal ions. Especially, the dimeric system 2 displayed a selective fluorescent enhancement and colorimetric change upon the addition of Hg²⁺, in which the spirolactam (nonfluorescent) to ring opened amide (fluorescent) process was utilized. The association constant of 2 with Hg²⁺ was calculated as 3.2 × 10⁵ M⁻¹.     

New fluorescent chemosensors for metal ions in solution

After a brief introduction on the main transduction mechanisms for metal ion detection by fluorescence, this paper reviews ligand molecules containing fluorophores synthesized and employed in metal ions sensing in solution in the last few years. With the aim of making more readable the paper we have organized it by dividing the subject first for type of fluorophore, then type of metal ion. Because of many acronyms a glossary has been inserted.     

A dansyl-based fluorescent film: Preparation and sensitive detection of nitroaromatics in aqueous phase

A novel fluorescent film sensor for the detection of nitroaromatics in aqueous phase has been developed via chemical immobilization of dansyl chromophores on an epoxy-terminated self-assembled monolayer on glass slide surfaces. Chemical attachment of the chromophore on the substrate surface endows the present film a satisfying stability and avoids the leaching of the chromophores. Increase in the length of the spacer connecting the sensing element and the substrate results in a dramatic improvement in the performance of the film compared to those with similar structures. Fluorescence quenching experiments demonstrates that in aqueous medium, the emission of the film is more sensitive to nitrobenzene (NB) than to other nitroaromatics, including 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, p-chloronitrobenzene, m-dinitrobenzene, p-dinitrobenzene, and o-chloronitrobenzene, etc. This exceptional result has been rationalized by considering the possible hindrance effect induced by the compact conformation of the long flexible spacer. It is also demonstrated that the NB quenching is static in nature, and the response of the film to NB is fast and reversible.     

Comparison of molecular imprinted particles prepared using precipitation polymerization in water and chloroform for fluorescent detection of nitroaromatics

A comparative study was conducted to study the effects that two different polymerization solvents would have on the properties of imprinted polymer microparticles prepared using precipitation polymerization. Microparticles prepared in chloroform, which previous results indicated was the optimal solvent for molecular imprinting of nitroaromatic explosive compounds, were compared to water, which was hypothesized to decrease water swelling of the polymer and allow enhanced rebinding of aqueous template. The microparticles were characterized and were integrated into a fluorescence sensing mechanism for detection of nitroaromatic explosive compounds. The performance of the sensing mechanisms was compared to illustrate which polymerization solvent produced optimal imprinted polymer microparticles for detection of nitroaromatic molecules. Results indicated that the structures of microparticles synthesized in chloroform versus water varied greatly. Sensor performance studies showed that the microparticles prepared in chloroform had greater imprinting efficiency and higher template rebinding than those prepared in water. For detection of 2,4,6-trinitrotoluene, the chloroform-based fluorescent microparticles achieved a lower limit of detection of 0.1 μM, as compared to 100 μM for the water-based fluorescent microparticles. Detection limits for 2,4-dinitrotoluene, as well as time response studies, also demonstrated that the chloroform-based particles are more effective for detection of nitroaromatic compounds than water-based particles. These results illustrate that the enhanced chemical properties of using the experimentally determined optimal polymerization solvent overcome deformation of imprinted binding sites by water swelling and benefits of using the polymerization solvent for rebinding of the template.     

Phenylene(vinylene) based fluorescent polymer for selective and sensitive detection of nitro‐explosive picric acid

We report the synthesis of phenylene(vinylene) based blue light emitting polymer by atom transfer radical polymerization with very good yield. Their photophysical properties were studied systematically with increasing polarities of solvent and sensing of nitro aromatics in solution and in vapor phase. The sensory properties of the polymer were studied toward various nitroaromatic compounds like nitrobenzene (NB), nitrotoluene (NT), dinitrobenzene (DNB), dinitrotoluene (DNT), nitro benzoic acid (NBA), 3‐nitro benzaldehyde (3‐NBA), trinitrotoluene (TNT), 4‐nitrophenol (NP), and picric acid (PA) in solution state. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3800–3807     

Novel highly selective fluorescent chemosensors for Zn(II)

Two novel fluorescent Zn²⁺ chemosensors were synthesized in four steps from inexpensive starting materials. They exhibited very strong fluorescence responses to Zn²⁺ and had remarkably high selectivity to Zn²⁺ than other metal ions including Mg²⁺, Ca²⁺, Ni²⁺, Cu²⁺, and Cd²⁺. These two new molecules could be used as low-priced yet high-quality Zn²⁺ chemosensors.     

Fluorescent signaling based on control of excited state dynamics. Biarylacetylene fluorescent chemosensors

We have previously reported that metal ion binding could restrict the excited state rotation of a biaryl chromophore, suppressing intersystem crossing and leading to increased emission. We have now applied the restriction of excited state dynamics to suppression of the other fundamental nonradiative decay pathway, internal conversion, in biarylacetylenes. This indicates that both nonradiative decay pathways are subject to conformational control, and that this signaling pathway should be generally accessible in simple flexible fluorophores.     

Fluorescein-based fluorescent and colorimetric chemosensors for copper in aqueous media

Two new fluorescein-based chemosensors for Cu²⁺ were designed with highly selective “off-on” behavior, one of them working in both absorption and emission, the other only in absorption. Binding to Cu²⁺ binding is reversible, as indicated by the bleaching of the color when the metal is extracted. The compounds form the basis for rapid, selective and sensitive Cu²⁺ chemosensors in aqueous media.