Pillararene-based fluorescent sensors for the tracking of organic compounds

Pillararenes form versatile receptors and an alteration of the fluorescence behavior upon complexation ensures the reporter function of these chemosensors.     

Synthesis and evaluation of a novel pyrenyl-appended triazole-based thiacalix[4]arene as a fluorescent sensor for Ag ion

New fluorescent chemosensors 1,3-alternate-1 and 2 with pyrenyl-appended triazole-based on thiacalix[4]arene were synthesized. The fluorescence spectra changes suggested that chemosensors 1 and 2 are highly selective for Ag⁺ over other metal ions by enhancing the monomer emission of pyrene in neutral solution. However, other heavy metal ions, such as Cu²⁺, and Hg²⁺ quench both the monomer and excimer emission of pyrene acutely. The ¹H NMR results indicated that Ag⁺ can be selectively recognized by the triazole moieties on the receptors 1 and 2 together with the ionophoricity cavity formed by the two inverted benzene rings and sulfur atoms of the thiacalix[4]arene.     

Rhodamine-based chemosensing monolayers on glass as a facile fluorescent “turn-on” sensing film for selective detection of Pb

Rhodamine-based chemosensors 1 and 2 were synthesized and self-assembled onto glass surfaces for the selective fluorescent sensing of Pb²⁺. The immobilized chemosensors showed fluorescent responses that were turned-on with Pb²⁺ in CH₃CN, selectively over various metal ions. The Pb²⁺-selective fluorescent switch of the immobilized chemosensors was also reversible, allowing for repeated use for Pb²⁺ detection.     

Synthesis and optical characterization of novel azacrown ethers containing an acridinone or an N-methylacridinone unit as potential fluorescent chemosensors

Four new achiral and four new chiral monoazacrown ethers containing an acridinone or an N-methylacridinone fluorescent signalling unit were prepared by reacting chloromethyl-substituted acridinone derivatives with achiral monoazacrown ethers with different cavity sizes and enantiopure monoaza-18-crown-6 ethers having two methyl and two isobutyl groups on their chiral centres, respectively. The operation of these chemosensors is based on the photoinduced electron transfer (PET) process, thus they show fluorescence enhancement in the presence of cationic guests. Their fluorescent behaviour as well as their complexation properties towards selected metal ions and the enantiomers of α-(1-naphthyl)ethylammonium perchlorate and potassium mandelate were examined.     

Fluorescent PET chemosensors for lithium

The synthesis of the chiral diaza-9-crown-3 derivatives 1 (S,S) and 2 (R,R) is described. These sensors were designed as luminescent chemosensors for lithium where the fluorescence emission from the naphthalene moieties was ‘switched on’ upon Li⁺ recognition by the crown ether moiety in organic solvents, showing excellent selectivity over other group I and group II cations. Even though the recognition of Li⁺ was not achieved in water (pH 7.4) or aqueous alcohol solution, the fluorescence (which was switched on at pH 7.4) was substantially modulated by spherical anions, where the fluorescence emission was quenched in the presence of Br⁻ and I⁻ but less by Cl⁻ and not by acetate. This indicates that the emission was quenched by heavy-atom affect. The recognition of Li⁺ was also investigated by ¹H NMR in CD₃CN and by observing the changes in the circular dicromism spectra. For the former, the resonances for the crown ether moiety and α-methyl protons adjacent to the ring were sifted upfield and broadened, whereas for 1 the intensity of the CD signal for the π-π transition was substantially modulated upon Li⁺ recognition.     

Novel chemosensor for alkaline earth metal ion based on 9-anthryl aromatic amide using a naphthalene as a TICT control site and intramolecular energy transfer donor

Novel fluorescent chemosensors 1 and 2 with two different fluorophores (naphthalene and anthracene) at the both ends of polyether was synthesized. These compounds based on 9-anthryl aromatic amide adopted a naphthalene as a TICT controller and an intramolecular energy transfer source. Compound 1 shows high fluorescence efficiency upon complexation with metal ion, and the fluorescence efficiency of 2 is regulated by metal ionic size.     

Through bond energy transfer (TBET)-based fluorescent chemosensors

Excitation energy transfer is one of the crucial issues in photophysical and photochemical process of any muti-chromophoric molecular systems, such as energy harvester and fluorescent chemosensor. Through bond energy transfer (TBET)-based fluorescent chemosensors are composed of three main parts: energy donor, energy acceptor, and rigid linker. Comparing with the often used Förster resonance energy transfer (FRET) mechanism, TBET does not require spectral overlap, thus it may enable more possible combination of energy donors and acceptors to be employed and afford higher sensitivity toward targets through ratiometric fluorescence. In this review, we highlight the recent progress in the design and biological applications of the organic TBET-based fluorescent chemosensors during 2014–2019, which will provide profound guidance for designing powerful chemosensors as well as exploring further biological applications.     

基于喹啉和三唑环的开链冠醚对金属离子的选择传感

本文通过Click化学反应合成了一种含喹啉基和三唑基的开链冠醚, 考察和比较了主体化合物对镉等金属离子的荧光传感和选择性键合行为, 并通过荧光和核磁等手段研究了溶剂对其荧光传感的影响.     

识别过渡金属离子的1,8-萘二甲酰亚胺多胺衍生物荧光传感器的研究

A series of fluorescent chemosensors 1-3 were synthesized to detect transition metal ions. At the room temperature, fluorescence intensities of these chemosensors in acetonitrile without transition metal ions were found to be very weak, due to the process of the e±cient intramolecular photoinduced electron transfer (PET). However, after addition of the transition metal ions, the chemosensor 1-3 exhibits obvious fluorescence enhancement. Moreover, the intensity of the fluorescence emission of chemosensors increases significantly in the presence of Zn2+ and Cd2+. The fluorescent chemosensors with different polyamine as receptors show diverse a±nity abilities to the transition metal ions and signal the receptor-metal ion interaction by the intensity change of fluorescence emission.     

Squaraine-based colorimetric and fluorescent sensors for Cu-specific detection and fluorescence imaging in living cells

New squaraine-based chemosensors SQ1 and SQ2 functionalized with 2-picolyl units were first synthesized and used as highly selective and sensitive colorimetric and fluorometric dual-channel sensors for Cu²⁺-specific recognition in aqueous systems. Among a series of individual metal ions, only Cu²⁺ could result in dramatic color changes. We also evaluated their capability of biological applications and found that SQ2 could be successfully employed as a Cu²⁺-selective probe in the fluorescence imaging of living cells.     

Novel Fluorescent Chemosensors Based on Tryptophan Unit for Cu2+ and Fe3+ in Aqueous Solution

We reported four fluorescent chemosensors containing tryptophan units. The fluorescence spectrum titration experiments suggest that chemosensors 1, 2, 3 and 4 are highly selective for Cu²⁺ and Fe³⁺ over Li⁺, Na⁺, K⁺, Co²⁺, Zn²⁺, Ni²⁺, Hg²⁺ and Cr³⁺ via forming complexes with Cu²⁺ or Fe³⁺, which is confirmed by dramatical quench of fluoreseence in aqueous solution at pH 7.4, thus making all the chemosensors suitable for Cu²⁺ and Fe³⁺ fluorescent sensors.     

Analytical supramolecular chemistry: Colorimetric and fluorimetric chemosensors

Chemical sensing using indicators, or chemosensor, has rapidly developed over the past decades. Its chemistry covers a wide range of scientific fields, in which analytical and supramolecular chemistry are key ideas to create functional and smart chemosensors. The principle of such a chemosensor design consists of three major processes: (1) to separate analytes, (2) to capture a specific analyte from a complex mixture, and (3) to output a signal from a [chemosensor•analyte] complex. In this review, “Analytical Supramolecular Chemistry” as a new scientific area was proposed, enabling us to promote deep insights into the mechanistic understanding of chemosensors. This review describes the interesting and representative chemosensors involving significant photochemical and photophysical processes and recent our advances in analytical supramolecular chemistry.     

Dicarboxylated ethynylarenes as buffer-dependent chemosensors for Cd(II), Pb(II), and Zn(II)

Two dicarboxylated ethynylarenes were prepared efficiently from condensation of 1,3-bis(3-aminophenylethynyl)benzene with 2 equiv of either succinic anhydride or glutaric anhydride. These compounds behave as fluorescent chemosensors selective for Cd(II), Pb(II), and Zn(II) cations under buffered aqueous conditions, with analyte binding observed as bathochromically shifted, intensified fluorescence. It was noteworthy that the fluorescence responses varied significantly with buffer identity. A conformational restriction mechanism involving reversible interactions between the fluorophore, metal cation, and buffer itself is proposed.     

Highly sensitive detection of nitroaromatic explosives using an electrospun nanofibrous sensor based on a novel fluorescent conjugated polymer

An electrospun nanofibrous explosive sensor was first constructed based on a newly developed fluorescent conjugated polymer P containing heteroatom polycyclic units. Electrospinning by doping polymer P as a fluorescent probe in a polystyrene supporting matrix afforded a fluorescence nanofibrous film with unique porous structures, and effectively avoided the aggregation of polymer P. The novel explosive sensor exhibited stable fluorescence property, satisfactory reversibility with less than 5% loss of signal intensity after four quenching–regeneration cycles, and good reproducibility among three batches with a relative standard deviation of 2.8%. Such fabricated sensor also showed remarkable sensitivity toward a series of trace nitroaromatic explosive vapors, including picric acid (parts-per-trillion level) and 2,4,6-trinitrotoluene vapor (parts-per-billion level), as well as good selectivity with less than 10% response to typical interferents. Therefore, the present strategy extends the application of different kinds of conjugated polymers for the construction of optical chemosensors.     

Fluorescent anion chemosensors using 2-aminobenzimidazole receptors

Simple and easy-to-make fluorescent anion chemosensors using 2-aminobenzimidazole moieties as binding subunits showed selective anion-induced fluorescent changes. The receptors effectively recognized fluoride, chloride, bromide, acetate, dihydrogen phosphate ions with a 1:1 stoichiometry.     

Fe-selective naked-eye ‘off–on’ fluorescent probe: its crystal structure and imaging in living cells

Four novel rhodamine-active probes L1–L4 have been proposed and characterized as fluorescent chemosensors for Fe³⁺. An ‘off-on’ type fluorescent enhancement was observed, which was induced by the interactions between Fe³⁺ and the probe, proven to adopt a 1:1 binding stoichiometry. The recognition properties of the target compounds with metal ions have been investigated in methanol–water (1:1, v/v) solution by the fluorescence and ultraviolet spectrum. In addition, a plausible application of probes in the imaging of HepG2 (liver cells) under the condition of reoxygenation (95% air, 5% CO₂) exposed to Fe³⁺ ions was also demonstrated.     

Colorimetric detection of cyanide with N-nitrophenyl benzamide derivatives

A series of structurally simple N-nitrophenyl benzamide derivatives have been developed as chemosensors toward cyanide in aqueous environment by taking advantage of the cyanide's strong affinity toward the acyl carbonyl carbon. The high selectivity of these compounds toward CN⁻ makes it a practical system for monitoring CN⁻ concentrations in aqueous samples.     

Evidence for a Bulky Unit of a Pillar[5]arene Flipping in the Solid State

It is well known that pillar[5]arenes have two most stable conformations (pS and pR) in their crystal structures. Because of the intramolecular H‐bonding interactions, substituents, temperature, solvent and so on, the rotational behaviors of the phenolic units on pillararenes are also common. This paper showed some other kinds of conformations in the functionalized pillar[5]arenes and gave evidence for a bulky unit (1,4‐methoxycarbonylmethoxybenzene unit) flipping in the solid state. The presence of hydrogen bonding facilitated the intermolecular self‐assembly in terms of energy‐minimized packing in the crystals. Thus, the main driving force for the flipping of this bulky unit might be both the intramolecular hydrogen bonding between the phenolic units on pillararenes and quadrupolar hydrogen bonding between the host and water. This paper helps us to have a better understanding on the conformations of pillar[5]arenes.     

EPR and fluorescence study of molecular dynamics of lipids in bilayers adsorbed on porous silica gel

Lipid bilayers immobilized on highly porous silica gel monoliths (SLBs) have been proposed as templates for chemosensors. Procedures for preparation and characterization of SLBs have been developed and applied. Rotational dynamics and orientational ordering at different depths in a SLB membrane and, for comparison, in bilayer liposomes have been studied for the first time using n-PC phospholipid spin labels.     

Synthesis and optical characterization of novel enantiopure BODIPY linked azacrown ethers as potential fluorescent chemosensors

Two novel enantiopure BODIPY linked azacrown ether chemosensors were prepared by reacting 3-chloro-5-methoxyBODIPY with new enantiopure monoaza-18-crown-6 ether ligands bearing two methyl and isobutyl groups on their chiral centres, respectively. The latter compounds were synthesized starting from optically active tetraethylene glycols in six steps. The operation of chemosensors is based on the intramolecular charge transfer (ICT) process. They exhibit pronounced off-on type fluorescent responses to some metal ions and chiral primary aralkyl ammonium ions, in particular to Ca²⁺ and Pb²⁺. Even in the case of 1:1 ratio of Ca²⁺ and Pb²⁺ ions to the ionophores, the fluorescence intensities and quantum yield values increased more than 10-fold, as well as both the absorption and emission bands were blue-shifted by about 20-30 nm (hipsochromic effect) in acetonitrile. The formation of relatively stable complexes allowed the determination of log K_s values by the mole-ratio method.