Investigation of cation binding and sensing by new crown ether core substituted naphthalene diimide systems

Different modes of cation binding lead to very different optical readouts from two structurally similar sensors.

Self-assembly of platinum(ii) 6-phenyl-2,2'-bipyridine complexes with solvato- and iono-chromic phenomena

Mono- and di-nuclear organoplatinum(ii) monomers with cyclometalated 6-phenyl-2,2'-bipyridine ligands have been successfully constructed. These systems are capable of displaying intriguing solvato- and iono-chromic phenomena by elaborately manipulating non-covalent PtPt metal-metal and π-π stacking interactions for their self-assembly processes.

Optically active crown ether-based fluorescent sensor molecules: A mini-review

This mini-review focuses on fluorescent optically active crown ethers (polymeric derivatives are not included) reported in the literature (according to our knowledge), of which enantiomeric recognition ability, and in some cases, also inorganic cation complexation properties, were investigated by the sensitive and versatile fluorescence spectroscopy. These crown ether-based chemosensors contain various fluorophore signaling units such as binaphthyl, anthracene, pyrene, tryptophan, benzimidazole, terpyridine, acridine, phenazine, acridone, BODIPY, and another conjugated aromatic one.

Ethynylpyrene Linked Benzocrown Ethers as Fluorescent Sensors for Metal Ions

Substances containing ethynylpyrenes linked to either one or four benzocrown ethers were synthesized, and their absorption and fluorescence spectroscopic responses to metal ions were assessed. Addition of metal perchlorates to solutions of these substances promotes short wavelength shifts in their absorption and fluorescence maxima and increases in their fluorescence intensities. The magnitudes of the fluorescence intensity increases are dependent on the ring size and number of the crown ether and the nature of the metal cation. Association constants for complex formation were calculated using fluorescence intensity versus concentration data. Analysis using Job's plots showed that the substances containing one benzocrown ether moiety form 1:1 complexes with metal ions. Results of experiments employing repeated addition and removal of Mg(ClO₄ )₂ demonstrate that the ON-OFF fluorescence response can be repeated at least three times. Results of molecular orbital calculations show that complexation with metal ions lowers the energies of both the π and π* levels of the ethynylpyrene moiety and that in some cases the vacant orbital on the metal becomes the LUMO of the complex. An explanation of the spectroscopic changes promoted by metal ions is proposed in terms of electrostatic repulsion and structural regulation.

Mix-&-Read Determination of Mercury(II) at Trace Levels with Hybrid Mesoporous Silica Materials Incorporating Fluorescent Probes by a Simple Mix-&-Load Technique

The synthesis, characterization, and application of mesoporous materials containing boron-dipyrromethene (BODIPY) moieties that allow the sensitive and selective detection of HgII in aqueous environments by fluorescence enhancement is reported. For this purpose, BODIPY dye I containing a thia-aza crown ether receptor as the fluorescent probe for the detection of HgII in aqueous environments is encapsulated into mesoporous materials to avoid self-quenching or aggregation in water. Determination of HgII is accomplished within a few seconds with high selectivity and sensitivity, reaching a limit of detection of 12 ppt. The determination of trace amounts of HgII in natural waters and in fish extracts is demonstrated by using our sensing material. The incorporation of the material into several μ-PAD strips yields a portable, cheap, quick, and easy-to-handle tool for trace HgII analysis in water.

Fluorescent Chemosensors for Various Analytes Including Reactive Oxygen Species, Biothiol, Metal Ions, and Toxic Gases

The development of fluorescent chemosensors for various analytes has been actively pursued by chemists. Since their inception, these efforts have led to many new sensors that have found wide applications in the fields of chemistry, biology, environmental science, and physiology. The search for fluorescent chemosensors was initiated by a few pioneering groups in the late 1970s and 1980s and blossomed during the last two decades to include more than hundreds of research groups around the world. The targets for these sensors vary from metal ions, anions, reactive oxygen/nitrogen species, biothiols, and toxic gases. Our group has made contributions to this area in last 18 years. In this perspective, we briefly introduce the history of chemosensors and review studies that we have carried out.

Recent Advances in the Development of Optical Imaging Probes for γ-Glutamyltranspeptidase

γ-Glutamyltranspeptidase (GGT) is a cell-membrane-bound protease that participates in cellular glutathione and cysteine homeostasis, which are closely related to many physiological and pathological processes. The accurate measurement of GGT activity is useful for the early diagnosis of diseases. In the past few years, many efforts have been made to build optical imaging probes for the detection of GGT activity both in vitro and in vivo. In this Minireview, recent advances in the development of various optical imaging probes for GGT, including activatable fluorescence probes, ratiometric fluorescence probes, and activatable bioluminescence probes, are summarized. This review starts from the instruction of the GGT enzyme and its biological functions, followed by a discussion of activatable fluorescence probes that show off-on fluorescence in response to GGT. GGT-activatable two-photon fluorescence imaging probes with improved imaging depth and spatial resolution are also discussed. Ratiometric fluorescence probes capable of accurately reporting on GGT levels through a self-calibration mechanism are discussed, followed by describing GGT-activatable bioluminescence probes that can offer a high signal-to-background ratio to detect GGT in living mice. Finally, current challenges and further perspectives for the development of molecular imaging probes for GGT are addressed.

Mix-&-Read Determination of Mercury(II) at Trace Levels with Hybrid Mesoporous Silica Materials Incorporating Fluorescent Probes by a Simple Mix-&-Load Technique

The synthesis, characterization, and application of mesoporous materials containing boron-dipyrromethene (BODIPY) moieties that allow the sensitive and selective detection of HgII in aqueous environments by fluorescence enhancement is reported. For this purpose, BODIPY dye I containing a thia-aza crown ether receptor as the fluorescent probe for the detection of HgII in aqueous environments is encapsulated into mesoporous materials to avoid self-quenching or aggregation in water. Determination of HgII is accomplished within a few seconds with high selectivity and sensitivity, reaching a limit of detection of 12 ppt. The determination of trace amounts of HgII in natural waters and in fish extracts is demonstrated by using our sensing material. The incorporation of the material into several μ-PAD strips yields a portable, cheap, quick, and easy-to-handle tool for trace HgII analysis in water.

A Ratiometric Fluorescent Probe for K+ in Water Based on a Phenylaza-18-Crown-6 Lariat Ether

This work presents two molecular fluorescent probes 1 and 2 for the selective determination of physiologically relevant K⁺ levels in water based on a highly K⁺ /Na⁺ selective building block, the o-(2-methoxyethoxy)phenylaza-18-crown-6 lariat ether unit. Fluorescent probe 1 showed a high K⁺ -induced fluorescence enhancement (FE) by a factor of 7.7 of the anthracenic emission and a dissociation constant (K_d ) value of 38 mm in water. Further, for 2+K⁺ , we observed a dual emission behavior at 405 and 505 nm. K⁺ increases the fluorescence intensity of 2 at 405 nm by a factor of approximately 4.6 and K⁺ decreases the fluorescence intensity at 505 nm by a factor of about 4.8. Fluorescent probe 2+K⁺ exhibited a K_d value of approximately 8 mm in Na⁺ -free solutions and in combined K⁺ /Na⁺ solution a similar K_d value of about 9 mm was found, reflecting the high K⁺ /Na⁺ selectivity of 2 in water. Therefore, 2 is a promising fluorescent tool to measure ratiometrically and selectively physiologically relevant K⁺ levels.

Rational Design of Hemicyanine Langmuir Monolayers by Cation-Induced Preorganization of Their Structure for Sensory Response Enhancement

This study takes a novel approach to the enhancement of receptor properties of thin-film sensors based on hemicyanine dyes with dithia-aza-crown-ionophoric moiety. By means of in situ UV-vis and X-ray reflectivity (XRR) measurements, it was revealed that the introduction of up to 0.25 mmol of Hg²⁺ under a preliminarily compressed monolayer, formed on pure water, does not lead to cation binding. This is due to the formation of "head-to-tail" aggregates (H-type), in which ionophoric group is blocked by the neighboring molecule. However, the presence of barium cations in the subphase under the forming Langmuir monolayer of the mentioned compound causes codirectional (head-to-head) orientation of chromoionophore fragments. This provides preorganization of a monolayer structure that facilitates the binding of complementary mercury cations, even in a compressed state: asymmetric sandwich complexes containing two dye molecules coordinate a Hg²⁺ cation between them. This complex structure was confirmed by molecular modeling based on the electron density distribution calculated from XRR measurement data. Such preorganization of supramolecular ensembles induced by cations, which do not participate in the complex formation with macroheterocyclic receptors, may have applications in fields where strict control of molecular orientation at the interface is required, such as nanoelectronics, sensorics, catalysis, etc.

Fluorescence chemosensor containing 4-methyl-7-coumarinyloxy, acetylhydrazono and N-phenylaza-15-crown-5 moieties for K+ and Ba2+ ions

A new aza-15-crown-5 derivative 1 bearing coumarin and hydrazone moieties was synthesized and characterized. The fluorescent sensing behavior and selectivity of 1 toward different metal ions in ethanol were investigated. There are 4-fold and 2-fold fluorescence enhancements of 1 at λem=406 nm upon addition of five equivalents of K+ and Ba2+, respectively. The fluorescence titration revealed the stoichiometry of 1:1 for 1-K+1-Ba2+ complexes and the binding constants (lgKs) of 4.11 for 1-K+ and 3.61 for 1-Ba2+. Compound 1 can be used as a fluorescent chemosensor for K+ and Ba2+ through discriminable photoresponse signals. The calculated detection limits for K+ and Ba2+ are 2.28 μm and 5.21 μm, respectively.

Positively Charged Hyperbranched Polymers with Tunable Fluorescence and Cell Imaging Application

Fluorescence-tunable materials are becoming increasingly attractive because of their potential applications in optics, electronics, and biomedical technology. Herein, a multicolor molecular pixel system is realized using a simple copolymerization method. Bleeding of two complementary colors from blue and yellow fluorescence segments reproduced serious multicolor fluorescence materials. Interestingly, the emission colors of the polymers can be fine-tuned in the solid state, solution phase, and in hydrogel state. More importantly, the positive fluorescent polymers exhibited cell-membrane permeable ability and were found to accumulate on the cell nucleus, exhibiting remarkable selectivity to give bright fluorescence. The DNA/RNA selectivity experiments in vitro and in vivo verified that [tris(4-(pyridin-4-yl)phenyl)amine]-[1,8-dibromooctane] has prominent selectivity to DNA over RNA inside cells.

Cation-Modulated Rotary Speed in a Light-Driven Crown Ether Functionalized Molecular Motor

The design and synthesis of an overcrowded-alkene based molecular motor featuring a crown ether integrated in its stator structure has been accomplished. The photostationary state ratios and rotational speed of this motor can be modulated by cation coordination to the crown ether moiety, which can be reversed upon the addition of a competing chelating agent, thus achieving a dynamic control over the rotational behavior of the motor.

Control of the Near Infrared Photoluminescence of Locally Functionalized Single-Walled Carbon Nanotubes via Doping by Azacrown-Ether Modification

Doped semiconducting single-walled carbon nanotubes (SWNTs) through local chemical functionalization (lf-SWNTs) show fascinating photoluminescence (PL) that appears with a longer wavelength and enhanced quantum yield compared to the original PL of non-modified SWNTs. In this study, we introduce an azacrown ether moiety at the doped sites of lf-SWNTs (CR-lf-SWNTs), and observe selective PL wavelength shifts depending on different interaction modes of silver ion inclusion and protonation of the amino group in the ring. Interestingly, their different values of the wavelength shifts show a clear correlation with calculated electron density of the nitrogen atom in the azacrown moiety in case of the inclusion form and the protonated form. This newly-observed responsiveness based on molecular interactions is expected to create doped sites that can versatilely control the PL functions based on molecular systems.

Chelating Rotaxane Ligands as Fluorescent Sensors for Metal Ions

Although metal-ion-binding interlocked molecules have been under intense investigation for over three decades, their application as scaffolds for the development of sensors for metal ions remains underexplored. In this work, we demonstrate the potential of simple rotaxanes as metal-ion-responsive ligand scaffolds through the development of a proof-of-concept selective sensor for Zn2+ .

Substituent Effect in the First Excited Singlet State of Monosubstituted Benzenes

sEDA, pEDA, and cSAR descriptors of the substituent effect were determined for >30 monosubstituted benzenes in the first excited singlet S₁ state at the LC-ωB97XD/aug-cc-pVTZ level. It was found that in the S₁ state, the σ- and π-valence electrons are a bit less and a bit more affected, respectively, than in the S₀ state, but basically, the effect in both states remains the same. In the S₀ and S₁ states, the d(C-X) distances to the substituent's first atom and the ring perimeter correlate with the sEDA and pEDA in the appropriate states, respectively. The energies and the gap of the frontier orbitals in the two states are linearly correlated and for the HOMO(S₁), LUMO(S₁), and HOMO(S₁)-LUMO(S₁) gap correlate also with the pEDA(S₁) and cSAR(S₁) descriptors. In all studied correlations, three similar groups of substituents can be distinguished, for which correlations (i) are very good, (ii) deviate slightly, and (iii) deviate significantly. Comparison of the shape of the HOMO(S₀) and HOMO(S₁) orbitals shows that for case (i) HOMO orbitals exhibit almost perfect antisymmetry against the benzene plane, for case (ii) the antisymmetry of HOMO in one of the states is either perturbed or changed, and for case (iii) one HOMO state has σ-character.

A Highly Selective Fluorescent Probe for Zn2+ Based on a Rhodamine-6G dye Derivative Modified by a Furan Unit

A fluorescent probe for Zn2+ based on rhodamine-6G has been synthesised. It showed excellent fluorescent specific selectivity and high sensitivity for Zn2+ compared with other metal ions, such as Fe3+, Cr3+, Hg2+, Ag+, Ca2+, Cu2+, Pb2+, Cd2+, Ni2+, Co2+ and Mg2+, in CH3CN–phosphate buffer saline solution. The distinct colour change and the rapid emergence of fluorescence emission provided ‘naked-eye’ detection of Zn2+. The detection limit of the fluorescent probe towards Zn2+ was 1.78 μM. In addition, the fluorescence lifetime and fluorescence quantum yield were measured.

Formation of macrocyclic ring systems by carbonylation of trifunctional P/B/B frustrated Lewis pairs

The trifunctional P/B/B frustrated Lewis pairs 11a-c featuring bulky aryl groups at phosphorus [Dmesp (a), Tipp (b), Mes* (c)] react with H2 by heterolytic hydrogen splitting followed by cleavage of HB(C6F5)2 to give the zwitterionic six-membered heterocyclic PH phosphonium/borate products 14a-c. Compounds 11a,b react with carbon monoxide by means of a Lewis acid induced CO insertion/rearrangement sequence that eventually results in the formation of the macrocyclic dimers 17a,b. The respective carbonylation reaction of the Mes*P/B/B FLP gives the macrocyclic trimer 18c. The new products were characterized spectroscopically and by X-ray diffraction and the reaction mechanism was analyzed by DFT calculations.

Entropy-Driven Reversible Agglomeration of Crown Ether Capped Gold Nanoparticles

It is shown that plasmonic gold nanoparticles functionalised with a thiolated 18-crown-6 ligand shell agglomerate spontaneously from aqueous dispersion at elevated temperatures. This process takes place over a narrow temperature range, is accompanied by a colour change from red to purple-blue and is fully reversible. Moreover, the temperature at which it occurs can be adjusted by the degree of complexation of the crown ether moiety with appropriate cations. More complexation leads to higher transition temperatures. The process has been studied by UV/Vis spectroscopy, electron microscopy, dynamic light scattering and zeta potential measurements. A thermodynamic rationale is provided to suggest an entropy-driven endothermic agglomeration process based on attractive hydrophobic interactions of the complexed crowns that are competing against electrostatic repulsion of the charged ligand shells.

Preparation of Cyano-Substituted Tetraphenylethylene Derivatives and Their Applications in Solution-Processable OLEDs

Creation of organic luminescent materials with high solid-state efficiency is of vital importance for their applications in optoelectronic fields. Here, a series of AIE luminogens (AIE gens), (Z)-2,3-bis(4-(9,9-bis(6-(9H-carbazol-9-yl)hexyl)-9H-fluoren-2-yl)phenyl)-3-phenylacrylonitrile (SFC), and 2,3-bis(4-(9,9-bis(6-(9H-carbazol-9-yl)hexyl)-9H-fluoren-2-yl)phenyl)fumaronitrile (DFC), utilizing 2,3,3-triphenylacrylonitrile and 2,3-diphenylfumaronitrile as respective centers, are designed and synthesized by Suzuki coupling reactions with high yields. The cis- and trans-isomers of DFC are also successfully obtained. All of them are thermally stable and show good solubility in common organic solvents. They all emit weakly in solution, but become strong emitters when fabricated into solid films. It is found introduction of one additional cyano group in DFC induced a big red-shift in solid-state emission, owing to its high electron-withdrawing ability. The cis- and trans-DFC show similar photophysical and Cyclic voltammogram (CV) behaviors. Non-doped solution-processed organic light-emitting diodes (OLEDs) using the three compounds as light-emitting layers are fabricated. SFC gives the best device performance with a maximum luminance of 5201 cd m⁻², a maximum current efficiency of 3.67 cd A⁻¹ and a maximum external quantum efficiencies (EQE) of 1.37%. Red-shifted EL spectra are observed for cis- and trans-DFC-based device, and the OLED using trans-DFC as active layer exhibits better performance, which might derive from their different conformation in film state.

Azo group(s) in selected macrocyclic compounds

Azobenzene derivatives due to their photo- and electroactive properties are an important group of compounds finding applications in diverse fields. Due to the possibility of controlling the trans-cis isomerization, azo-bearing structures are ideal building blocks for development of e.g. nanomaterials, smart polymers, molecular containers, photoswitches, and sensors. Important role play also macrocyclic compounds well known for their interesting binding properties. In this article selected macrocyclic compounds bearing azo group(s) are comprehensively described. Here, the relationship between compounds' structure and their properties (as e.g. ability to guest complexation, supramolecular structure formation, switching and motion) is reviewed.

A uniquely fabricated Cu(ii)-metallacycle as a reusable highly sensitive dual-channel and practically functional metalloreceptor for Fe3+ and Ca2+ ions: an inorganic site of cation detection

Dimeric Cu(ii)-complex developed from disulfane ligand, serves as dual-channel metalloreceptor for Fe³⁺/Ca²⁺ and detection of Fe³⁺ in real water samples.

A supramolecular red to near-infrared fluorescent probe for the detection of drugs in urine

A host–guest complex based on a newly designed and synthesized cationic perylene dye and cucurbit[8]uril exhibits red-NIR emission, high affinity and stability, and large Stokes shift. It can serve as a red-NIR fluorescent displacement probe for the detection of drugs in urine.

A three-dimensional (time, wavelength and intensity) functioning fluorescent probe for the selective recognition/discrimination of Cu2+, Hg2+, Fe3+ and F− ions

A new probe for the selective recognition/discrimination of Cu²⁺, Hg²⁺, Fe³⁺ and F⁻ ions by measuring their response time, wavelength and fluorescence intensity.

Prediction and understanding of AIE effect by quantum mechanics-aided machine-learning algorithm

An efficient machine learning scheme using a SVM classifier for predicting the aggregation-induced emission effect of triphenylamine-based luminophores was proposed.

A thiocoumarin-based colorimetric and ratiometric fluorescent probe for Hg2+ in aqueous solution and its application in live-cell imaging

A new intramolecular charge transfer (ICT) based colorimetric and ratiometric fluorescent chemodosimeter for the detection of Hg²⁺ has been rationally designed and developed.

A novel ESIPT-based fluorescent chemodosimeter for Hg2+ detection and its application in live-cell imaging

A novel ESIPT-based fluorescent chemodosimeter for the detection of Hg²⁺ has been rationally designed and developed.

Synthesis, X-ray crystallography, thermogravimetric analysis and spectroscopic characterization of isostructural one-dimensional coordination polymers as sorbents for some anions

A new series of coordination polymers capable of adsorbing anions have been synthesized by employing a dipyridine substituted diazacrown macrocycle as linker.

Synthesis, crystal structures, one/two-photon optical properties and bioimaging application of two organic molecules with D–A and D–π–A models containing 6-phenyl-2,2′-bipyridine

The structures, one/two-photon optical properties and bioimaging application of two organic molecules with D–A and D–π–A models containing 6-phenyl-2,2′-bipyridine were studied.

CdII/ZnIIdiscrimination using 2,5-diphenyl[1,3,4]oxadiazole based fluorescent chemosensors

Two ditopic PPD based ligands are able to discriminate Cd^IIover Zn^IIin aqueous solution based on the difference in their ionic radii, acting as OFF–ON fluorescent probes.

Tri-pillar[5]arene-based multi-stimuli-responsive supramolecular polymers for fluorescence detection and separation of Hg2+

A novel tri-pillar[5]arene based supramolecular polymer (JP5G) shows multiple stimuli-response properties and could detect and remove Hg²⁺ from aqueous solution.

A fast response fluorescence probe specific for hypochlorous acid detection and its applications in bioimaging

The features ofDNPH-NA, including its high sensitivity, selectivity, and reliability at physiological pH, together with a rapid response, enable its successful application in the detection of endogenous HOClin vitroandin vivo.

Solvent directed selective and sensitive fluorescence detection of target ions using a coumarin–pyridine probe

The solvatochromic properties of a coumarin–pyridine probe were utilized as a cheap and effective way for designing fluorescent probes for Mg²⁺ and PPi with high selectivity and nanomolar level sensitivity.