Rhodamine hydrazone derivatives as Hg2+ selective fluorescent and colorimetric chemosensors and their applications to bioimaging and microfluidic system

In this paper, we report new rhodamine hydrazone derivatives bearing thiol and carboxylic acid groups as selective fluorescent and colorimetric chemosensors for Hg(2+). The ring-opening process of spirolactam enables the large fluorescent enhancement and colorimetric change upon the addition of Hg(2+). The sample containing Hg(2+) was mixed with one of the chemosensors in a microchannel where the sensor was examined using confocal laser scanning microscopy. A plot of the fluorescent intensities of both chemosensors versus the log concentration of Hg(2+) exhibited a linear response (r(2)=0.95) in the range of 1 nM-1 μM, and the detection limits were 1 nM and 4.2 nM, respectively. Both chemosensors also enable the visualization of Hg(2+) accumulated in the nematode Caenorhabditis elegans previously exposed to nanomolar concentrations of Hg(2+).     

New acridine derivatives bearing immobilized azacrown or azathiacrown ligand as fluorescent chemosensors for Hg and Cd

Two new acridine derivatives bearing azacrown or azathiacrown ligand were synthesized as fluorescent chemosensors for Hg²⁺ and Cd²⁺ in aqueous solution. Compounds 1 and 2 displayed selective CHEF (chelation enhanced fluorescence) effects with Hg²⁺ or Cd²⁺ among the metal ions examined. The practical use of these probes was demonstrated by their applications to the detection of Hg²⁺ and Cd²⁺ ions in mammalian cells.     

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.     

Anthracene derivatives bearing thiourea group as fluoride selective fluorescent and colorimetric chemosensors

New anthracene derivatives bearing thiourea group have been synthesized and characterized including X-ray crystallography. These chemosensors display selective ratiometric changes in their fluorescence spectra upon the addition of fluoride ion.     

Anthracene derivatives bearing two urea groups as fluorescent receptors for anions

For the recognition and sensing of anionic analytes, comparative studies were carried out on the anion bindings of pyrophosphate, H₂PO₄⁻, and dicarboxylates to the anthracene derivatives bearing two urea groups on the 1,8 and 9,10-positions as fluorescent chemosensors for anions. Their binding properties were compared using fluorescence and ¹H NMR, and the results were rationalized with an ab initio study.     

Anthracene derivatives bearing sulfur atoms or selenium atoms as fluorescent chemosensors for Cu and Hg: different selectivity induced from ligand immobilization onto anthracene

Two new selenium containing anthracene derivatives and two new sulfur containing anthracene derivatives were synthesized as fluorescent chemosensors for Hg²⁺ and Cu²⁺. Compound 1 displayed a highly selective chelation enhanced fluorescence quenching (CHEQ) effect only with Cu²⁺, on the other hand, compounds 3 and 4 displayed highly selective chelation enhanced fluorescence (CHEF) effects only with Hg²⁺ among the metal ions examined.     

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.     

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.     

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.     

New photochromic chemosensors for Hg and F

Two new chemosensors (1a and 1b) based on photochromic dithienylcyclopentene were designed and synthesized, and their spectral behaviors toward various metal ions and anions were investigated in detail. Compounds show excellent optical properties and distinguish Hg²⁺ and F⁻ in CH₃CN. Job’s plot reveals that the presence of Hg²⁺ induces the formation of a 1:1 complex between 1a or 1b and Hg²⁺. From the spectral responses and ¹H NMR analysis, the deprotonation of the thioamide protons is proposed to explain the sensing mechanism for 1a and 1b toward F⁻. It is found that 1a and 1b exhibit ring-opening and ring-closing photoisomerization with UV-vis light irradiation. Furthermore, their photochromic properties can be modulated by Hg²⁺ and F⁻ ions. Moreover, 1a and 1b in photostationary states become promising sensors for Hg²⁺ and F⁻ with high selectivity.     

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.     

Hg sensing in aqueous solutions: an intramolecular charge transfer emission quenching fluorescent chemosensors

Compounds 4a and 4b, comprising an anthracene moiety as the fluorophore and a pair of dithiocarbamate functionalities as ligating groups, were designed as fluorescent chemosensors for Hg(II). In aqueous solvent systems, upon excitation, in addition to the normal emission bands of locally excited (LE) state of anthracene, both compounds show a prominent pH-independent intramolecular charge transfer (ICT) emissive band, which can be modulated by Hg²⁺ binding. The systems can be exploited to develop a fluorescent sensitive probe for Hg²⁺.     

Theoretical study of thiazole derivatives as chemosensors for fluoride anion

The interactions between chemosensor, 2-(2′-hydroxyphenyl)-4-phenylthiazole (1), and different halides (F⁻, Cl⁻, and Br⁻) and NO₃⁻ anions have been theoretically investigated at the B3LYP/6-31G(d) level with the BSSE correction. It turned out that the unique selectivity of 1 for F⁻ is ascribed to its ability of deprotonating the hydroxy group of host sensor. The intermolecular proton transfer (IPT) causes the colorimetric and fluorescent signaling of 1 for F⁻. The deprotonated complex 1⁻·HF is formed for the deprotonation process of chemosensor. The study of substituent effects suggest that the electron-donating –CH₃ and –OCH₃ substituted derivatives are expected to be promising candidates for ratiometric fluorescent F⁻ chemosensors as well as chromogenic chemosensors, while electron-donating –N(CH₃)₂ substituted derivative can serve as chromogenic F⁻ chemosensors only. Furthermore, the electron-withdrawing (–NO₂ and –Br) substituted derivatives can serve as chromogenic F⁻/CH₃COO⁻ chemosensors.     

Bis(indolyl)methane derivatives as highly selective colourimetric and ratiometric fluorescent molecular chemosensors for Cu cations

New probes based on bis(indolyl)methane derivatives only sense Cu²⁺ among other heavy and transition metal (HTM) ions through two different channels: the colourless to orange or purple colour change, that is visible to the naked eye, and a remarkable enhancement of the fluorescence along with a large red-shift in emission, in a water containing medium (CH₃CN/H₂O).     

New cavitand derivatives bearing four coumarin groups as fluorescent chemosensors for Cu and recognition of dicarboxylates utilizing Cu complex

New cavitand derivatives (1, 2) bearing four coumarin groups were synthesized, and the binding properties of these cavitands towards metal ions were examined through their fluorescent changes. Cavitand 1 effectively recognized the Cu²⁺ ions among the metal ions examined. The recognition of cavitand 1-Cu²⁺ with dicarboxlyates is also described.     

8-Hydroxyquinoline benzoates as highly sensitive fluorescent chemosensors for transition metal ions

[graph: see text] 8-Hydroxyquinoline benzoates were developed as a new set of 8-HQ derivatives for highly sensitive fluorescent chemosensors for transition metal ions. A prominent fluorescence enhancement was found in the presence of transition metal ions such as Hg2+ and Cu2+, and this was suggested to result from the suppression of radiationless transitions from the npi state in the chemosensors.     

Highly sensitive and selective fluorescent chemosensors for Hg(II) in an aqueous environment based on carbamodithioate

Two highly sensitive (detection limits ∼20 nM) and selective (selectivity >30) fluorescent chemosensors were developed for detecting Hg²⁺ in a fully aqueous environment by using the rarely-studied carbamodithioate to create an Hg²⁺ binding site.     

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).     

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).     

9-diphenylaminoacridines as molecular fluorescent chemosensors for determining polar solvent and amine vapors

The results of study of the photophysical properties of three fluorophores from the 9-diphenylaminoacridine series in solutions are presented. It has been shown that the photoinduced synthesis of 9-diphenylaminoacridines in polymer films and on the surface of polymeric micro- and nanoparticles can be used for detection of polar solvent and amine vapors.