A detailed insight into anion sensing based on intramolecular charge transfer (ICT) mechanism: A comprehensive review of the years 2016 to 2021

A Ratiometric Fast-Response Fluorescent Probe Based on Dicyanoisophorone for Monitoring HClO in Paper Test Strips and Living Mice

A new dicyanoisophorone-based ratiometric fluorescent probe NOSA was synthesized and characterized. It showed a fast fluorescence response to HClO with the emission color change from dark green to bright red. NMR, IR, and HRMS suggested that the detection of NOSA to HClO may originate from the hydroxyl deprotection reaction by HClO on the molecule NOSA, which caused a red-shift of fluorescence. The probe NOSA displayed high selectivity and excellent anti-interference performance with a limit of detection at 3.835 × 10-7 M. The convenient paper test strips were successfully obtained and applied to the detection of HClO based on fluorescence color change with the varied NaClO concentration. Moreover, spiked recovery experiments in real water samples indicated that the probe NSOA could quantitatively detect HClO, and the fluorescence bio-imagings in vivo were carried out, and HClO detection in biosystems using NOSA was realized.

Developing NIR xanthene-chalcone fluorophores with large Stokes shifts for fluorescence imaging

A series of novel near-infrared (NIR) xanthene-chalcone fluorophores were constructed through a modular synthesis with the electron-donating xanthene moiety and the electron-withdrawing chalcone moiety. These fluorophores are convenient for fluorescence imaging in living cells, benefiting from their NIR emissions (650-710 nm), large Stokes shifts (>100 nm), moderate quantum yields and low cytotoxicity. The substituted hydroxyl group of the xanthene-chalcone fluorophore HCA-E facilitates the development of multifunctional fluorescent probes. As an example, a highly sensitive and selective probe N-HCA-E for glutathione (GSH) detection was developed based on the fluorophore HCA-E. A 4-nitrobenzenesulfonyl (4-Ns) group was introduced to cage the hydroxyl group of HCA-E, which was used as a selective recognition site for the thiol of GSH and an effective fluorescence quencher. Probe N-HCA-E revealed NIR "turn-on" fluorescence (709 nm) for endogenous and exogenous GSH detection in lysosomes with a large Stokes shift (129 nm) and high anti-interference ability.

Development of D-π-A organic dyes for discriminating HSA from BSA and study on dye-HSA interaction

HSA (human serum albumin), a most abundant protein in blood serum, plays a key role in maintaining human health. Abnormal HSA level is correlated with many diseases, and thus has been used as an essential biomarker for therapeutic monitoring and biomedical diagnosis. Development of small-molecule fluorescent probes allowing the selective and sensitive recognition of HSA in in vitro and in vivo is of fundamental importance in basic biological research as well as medical diagnosis. Herein, we reported a series of new synthesized fluorescent dyes containing D-π-A constitution, which exhibited different optical properties in solution and solid state. Among them, dye M-H-SO3 with a hydrophilic sulfonate group at electron-acceptor part displayed selectivity for discrimination of HSA from BSA and other enzymes. Upon binding of dye M-H-SO3 with HSA, a significant fluorescence enhancement with a turn-on ratio about 96-fold was triggered. The detection limit was estimated to be ∼ 40 nM. Studies on the interaction mechanism revealed that dye M-H-SO3 could bind to site III of HSA with a 1:1 binding stoichiometry. Furthermore, dye M-H-SO3 has been applied to determine HSA in real urine samples with good recoveries, which provided a useful method for HSA analysis in biological fluids.

Voltammetric Sensing of Chloride Based on a Redox-Active Complex: A Terpyridine-Co(II)-Dipyrromethene Functionalized Anion Receptor Deposited on a Gold Electrode

A redox-active complex containing Co(II) connected to a terpyridine (TPY) and dipyrromethene functionalized anion receptor (DPM-AR) was created on a gold electrode surface. This host-guest supramolecular system based on a redox-active layer was used for voltammetric detection of chloride anions in aqueous solutions. The sensing mechanism was based on the changes in the redox activity of the complex observed upon binding of the anion to the receptor. The electron transfer coefficient (α) and electron transfer rate constant (k0) for the modified gold electrodes were calculated based on Cyclic Voltammetry (CV) experiments results. On the other hand, the sensing abilities were examined using Square Wave Voltammetry (SWV). More importantly, the anion receptor was selective to chloride, resulting in the highest change in Co(II) current intensity and allowing to distinguish chloride, sulfate and bromide. The proposed system displayed the highest sensitivity to Cl- with a limit of detection of 0.50 fM. The order of selectivity was: Cl- > SO42- > Br-, which was confirmed by the binding constants (K) and reaction coupling efficiencies (RCE).

Excited-state dynamics of 4-hydroxyisoindoline-1,3-dione and its derivative as fluorescent probes

Fluorescent probes have become promising tools for monitoring the concentration of peroxynitrite, which is linked to many diseases. However, despite focusing on developing numerous peroxynitrite based fluorescent probes, limited emphasis is placed on their sensing mechanism. Here, we investigated the sensing mechanism of a peroxynitrite fluorescent probe, named BHID-Bpin, with a focus on the relevant excited state dynamics. The photoexcited BHID-Bpin relaxes to its ground state via an efficient nonradiative process (∼300 ps) due to the presence of a minimum energy conical intersection between its first excited state and ground state. However, upon reacting with peroxynitrite, the Bpin moiety is cleaved from BHID-Bpin and BHID is formed. The formed BHID exhibits strong dual band fluorescence which is caused by an ultrafast excited-state intramolecular proton transfer process (∼1 ps).

Recent Advancements in Fluorometric and Colorimetric Detection of Cd2+ Using Organic Chemosensors: A Review (2019-2024)

In recent decades, heavy metal ions have emerged as a significant global environmental concern, posing threats to the delicate balance of ecosystems worldwide. Their introduction into ecosystems occurs through various activities and poses a serious risk to human health. Among heavy metal ions, Cd2+ is recognized as a highly toxic pollutant. Its widespread use contributes to its accumulation in the environment. Chronic exposure to Cd2+ ions present serious risks to both the environment and human health. Therefore, the detection of these metal ions are very important. Organic fluorometric and colorimetric detection have emerged as promising tools for this purpose, offering advantages such as high sensitivity, selectivity, and sometimes reversibility. This review offers a comprehensive overview of the recent advancements in the fluorometric and colorimetric detection of Cd2+ using organic chemosensors from 2019 to 2024. We delve into key aspects of these studies, including the design strategies employed to design novel chemosensors and the underlying sensing mechanisms. Furthermore, we explore the diverse applications of these organic chemosensors, ranging from environmental monitoring to biomedical diagnostics. By analyzing the latest research findings, this review aims to offer insights into the current state-of-the-art in the field of Cd2+ detection using organic chemosensors. Additionally, it highlights the potential opportunities and challenges that lie ahead, paving the way for future advancements in this important area of research.

Multifunctional Biomolecules Bridging a Buried Interface for Efficient Perovskite Solar Cells

The inevitably positively and negatively charged defects on the SnO2/perovskite buried interface often lead to nonradiative recombination of carriers and unfavorable alignment of energy levels in perovskite solar cells (PSCs). Interface engineering is a reliable strategy to manage charged defects. Herein, the nicotinamide adenine dinucleotide (NAD) molecules with multiple active groups of ─P=O, ─P-O, and ─NH2 are introduced to bridge the SnO2/perovskite buried interface for achieving simultaneous elimination of positively and negatively charged defects. We demonstrate that the ─P=O and ─P-O groups in NAD not only fix the uncoordinated Pb2+ but also fill the oxygen vacancies (VO) on the SnO2 layer to eliminate positively charged defects. Meanwhile, ─NH2 groups form hydrogen bonds with PbI2 to reduce the number of negatively charged defects. In addition, the NAD biomolecules as a bridge induce high perovskite crystallization and accelerated electronic transfer along with favorable energy band alignment between SnO2 and perovskite. Finally, the PSCs with the ITO/SnO2/NAD/Cs0.15FA0.75MA0.1PbI3/Spiro-OMeTAD/Ag structure deliver an improvement in the power conversion efficiency from 20.49 to 23.18% with an excellent open-circuit voltage (Voc) of 1.175 V. This work demonstrates that interface engineering through multifunctional molecular bridges with various functional groups is an effective approach to improve the performance of PSCs by eliminating charged defects and simultaneously regulating energy level alignment.

Recent Advancements and Future Prospects in NBD-Based Fluorescent Chemosensors: Design Strategy, Sensing Mechanism, and Biological Applications

In recent years, the field of Supramolecular Chemistry has witnessed tremendous progress owing to the development of versatile optical sensors for the detection of harmful biological analytes. Nitrobenzoxadiazole (NBD) is one such scaffold that has been exploited as fluorescent probes for selective recognition of harmful analytes and their optical imaging in various cell lines including HeLa, PC3, A549, SMMC-7721, MDA-MB-231, HepG2, MFC-7, etc. The NBD-derived molecular probes are majorly synthesized from the chloro derivative of NBD via nucleophilic aromatic substitution. This general NBD moiety ligation method to nucleophiles has been leveraged to develop various derivatives for sensing analytes. NBD-derived probes are extensively used as optical sensors because of remarkable properties like excellent stability, large Stoke's shift, high efficiency and stability, visible excitation, easy use, low cost, and high quantum yield. This article reviewed NBD-based probes for the years 2017-2023 according to the sensing of analyte(s), including cations, anions, thiols, and small molecules like hydrogen sulfide. The sensing mechanism, designing of the probe, plausible binding mechanism, and biological application of chemosensors are summarized. The real-time application of optical sensors has been discussed by various methods, such as paper strips, molecular logic gates, smartphone detection, development of test kits, etc. This article will update the researchers with the in vivo and in vitro biological applicability of NBD-based molecular probes and challenges the research fraternity to design, propose, and develop better chemosensors in the future possessing commercial utility.

Recent advances in the fluorimetric and colorimetric detection of cobalt ions

Cobalt is an essential metal to maintain several functions in the human body and is present in functional materials for numerous applications. Thus, to monitor these functions, it is necessary to develop suitable probes for the detection of cobalt. Presently, researchers are focused on designing different chemosensors for the qualitative and quantitative detection of the metal ions. Among the numerous methods devised for the identification of cobalt ions, colorimetric and fluorimetric techniques are considered the best choice due to their user-friendly nature, sensitivity, accuracy, linearity and robustness. In these techniques, the interaction of the analyte with the chemosensor leads to structural changes in the molecule, causing the emission and excitation intensities (bathochromic, hyperchromic, hypochromic, and hypsochromic) to change with a change in the concentration of the analyte. In this review, the recent advancements in the fluorimetric and colorimetric detection of cobalt ions are systematically summarized, and it is concluded that the development of chemosensors having distinctive colour changes when interacting with cobalt ions has been targeted for on-site detection. The chemosensors are grouped in various categories and their comparison and the discussion of computational studies will enable readers to have a quick overview and help in designing effective and efficient probes for the detection of cobalt in the field of chemo-sensing.

Recent advances in FRET probes for mitochondrial imaging and sensing

Mitochondria, as essential organelles in cells, play a crucial role in cellular growth and apoptosis. Monitoring mitochondria is of great importance, as mitochondrial dysfunction is often considered a hallmark event of cell apoptosis. Traditional fluorescence probes used for mitochondrial imaging and sensing are mostly intensity-based and are susceptible to factors such as concentration, the probe environment, and fluorescence intensity. Probes based on fluorescence resonance energy transfer (FRET) can effectively overcome external interference and achieve high-contrast imaging of mitochondria as well as quantitative monitoring of mitochondrial microenvironments. This review focuses on recent advances in the application of FRET-based probes for mitochondrial structure imaging and microenvironment sensing.

Design strategies and biological applications of β-galactosidase fluorescent sensor in ovarian cancer research and beyond

Beta-galactosidase (β-galactosidase), a lysosomal hydrolytic enzyme, plays a critical role in the catalytic hydrolysis of glycosidic bonds, leading to the conversion of lactose into galactose. This hydrolytic enzyme is used as a biomarker in various applications, including enzyme-linked immunosorbent assays (ELISAs), gene expression studies, tuberculosis classification, and in situ hybridization. β-Galactosidase abnormalities are linked to various diseases, such as ganglioside deposition, primary ovarian cancer, and cell senescence. Thus, effective detection of β-galactosidase activity may aid disease diagnoses and treatment. Activatable optical probes with high sensitivity, specificity, and spatiotemporal resolution imaging capabilities have become powerful tools for visualization and real time tracking in vivo in the past decade. This manuscript reviews the sensing mechanism, molecular design strategies, and advances of fluorescence probes in the biological application of β-galactosidase, particularly in the field of ovarian cancer research. Current challenges in tracking β-galactosidase and future directions are also discussed.

Study on the modulating effect of halogen atom substitution on the detection range of water content detection probes in organic solvents

Fluorescence probes based on the variations of aggregation state (Aggregation-Induced Emission (AIE) and Aggregation-Caused Quenching (ACQ)) have received widespread attention due to their simplicity, efficiency and intuitiveness. However, typical probes are highly sensitive to changes in polarity and slight variations in the external environment can cause a complete change in the aggregation state. With the aim of expanding the detection range of the molecular probe, this work adopts a different design strategy from adjusting the molecular backbone but regulates the fluorescence behavior of the Schiff base molecular backbone by introducing different halogen atoms. Systematic studies show that when chlorine serves as substitutional atoms (3,5-Cl Salen), the probe can achieve full-range detection of water content (0-100 vol%) in ethanol and DMF. To our knowledge, the 3,5-Cl Salen represents the best water content probe in organic molecules. Experimental and theoretical studies have shown that the adjustment of halogen atoms can linearly change the charge distribution on the benzene ring and precisely control the strength of intermolecular interactions. At the same time, we developed a fluorescent filter paper based on 3,5-Cl Salen and used smartphones for rapid, sensitive and precise on-site measurement of water content in organic solvents.

Fast and Selective Luminescent Sensing by Langmuir-Schaeffer Films Based on Controlled Assembly of Perylene Bisimide Modified with A Cyclometalated AuIII Complex

Condensed films of functional luminophores dominated by the magnitude and dimensionality of the intermolecular interactions play important roles in sensing performance. However, controlling the molecular assembly and regulating photophysical properties remain challenging. In this study, a new luminophore, ortho-PBI-Au, was synthesized by anchoring a cyclometalated alkynyl-gold(III) unit at the ortho-position of perylene bisimide. An unprecedented T-type packing model driven by weak Au-π interaction and Au-H bonds was observed, laying foundation for striking properties of the luminophore. Controlled assembly of ortho-PBI-Au at the air-water interface, realized using the classical Langmuir-Schaeffer technique, afforded the obtained luminescent films with different packing structures. With an optimized film, sensitive, selective, and rapid detection of a hazardous new psychoactive substance, phenylethylamine (PEA), was achieved. The detection limit, response time, and recovery time were <4 ppb, <1 s, and <5 s, respectively, surpassing the performance of the PEA sensors known thus far. The relationship between the characters of films and the sensing performance was systematically examined by grey relational analysis (GRA). The present study suggests that designing novel molecular aggregation with definite adlayer structure is a crucial strategy to enhance the sensing performance, which could be favorable for the film-based fluorescent sensors.

Halide Complexes of 5,6-Dicyano-2,1,3-Benzoselenadiazole with 1 : 4 Stoichiometry: Cooperativity between Chalcogen and Hydrogen Bonding

The [M4 -Hal]- (M=the title compound; Hal=Cl, Br, and I) complexes were isolated in the form of salts of [Et4 N]+ cation and characterized by XRD, NMR, UV-Vis, DFT, QTAIM, EDD, and EDA. Their stoichiometry is caused by a cooperative interplay of σ-hole-driven chalcogen (ChB) and hydrogen (HB) bondings. In the crystal, [M4 -Hal]- are connected by the π-hole-driven ChB; overall, each [Hal]- is six-coordinated. In the ChB, the electrostatic interaction dominates over orbital and dispersion interactions. In UV-Vis spectra of the M+[Hal]- solutions, ChB-typical and [Hal]- -dependent charge-transfer bands are present; they reflect orbital interactions and allow identification of the individual [Hal]- . However, the structural situation in the solutions is not entirely clear. Particularly, the UV-Vis spectra of the solutions are different from the solid-state spectra of the [Et4 N]+ [M4 -Hal]- ; very tentatively, species in the solutions are assigned [M-Hal]- . It is supposed that the formation of the [M4 -Hal]- proceeds during the crystallization of the [Et4 N]+ [M4 -Hal]- . Overall, M can be considered as a chromogenic receptor and prototype sensor of [Hal]- . The findings are also useful for crystal engineering and supramolecular chemistry.

Charge Transfer Process of a Solvated Hydrogen-Bonded Organic Network

We show the first example of an organic linker (OL) terminated by carboxylic groups that can form a hydrogen-bonded network/polymer (HBN) in solution under controlled conditions in which the photogenerated charges can hop from a monomer OL to the hydrogen-bonded backbone of OLs, as probed by transient absorption (fs-TA). While fs-TA reveals a slow twisting process in the monomer form of the OL, the formation of a hydrogen-bonded network in solution suppresses such process and favors instead a charge transfer (CT) state along the low-lying hydrogen-bonded backbone. Theoretical calculations show that such solvated HBN in a specific polar solvent is stabilized due to the huge change of the dipole moment from monomer compared to the network, leading to a charge delocalization character due to the symmetry breaking. Our findings will open new avenues for implementing solvated hydrogen-bonded molecules in applications such as sensing and photocatalysis.

Precise tumor delineation in clinical tissues using a novel acidic tumor microenvironment activatable near-infrared fluorescent contrast agent

Tumor selective near-infrared (NIR) fluorescent contrast agents has the potential to greatly enhance the efficiency and precision of tumor surgery by enabling real-time tumor margin identification for tumor resection guided by imaging. However, the development of these agents is still challenging. In this study, based on the acidic tumor microenvironment (TME), we designed and synthesized a novel pH-sensitive NIR fluorescent contrast agent OBD from β-carboline. The fluorescence quantum yield of OBD exhibited a notable increase at pH 3.6, approximately 12-fold higher compared to its value at pH 7.4. After cellular uptake, OBD lighted up the cancer cells with high specificity and accumulated in the mitochondria. Spraying OBD emitted selective fluorescence in xenograft tumor tissues with tumor-to-normal tissue ratios (TNR) as high as 11.18, implying successful image-guided surgery. Furthermore, OBD was also shown to track metastasis in spray mode. After simple topical spray, OBD rapidly and precisely visualized the tumor margins of clinical colon and liver tissues with TNR over 4.2. Therefore, the small-molecule fluorescent contrast agent OBD has promising clinical applications in tumor identification during surgery.

Facile synthesis and anion binding studies of fluorescein/benzo-12-crown-4 ether based bis-dipyrromethane (DPM) receptors

Two novel fluorescein as well as benzo-12-crown-4 ether functionalized dipyrromethane receptors (DPM3 and DPM4) have successfully been synthesized. The anion (used as their TBA salts) binding studies of thus prepared DPM3 and DPM4 receptors were evaluated by the UV-visible spectrophotometric titrations. Binding affinities as well as the stoichiometry were determined through the UV-visible titrations data with the involvement of the BindFit (v0.5) package available online at https://supramolecular.org. Moreover, binding events were validated by means of the comparison of the partial 1H-NMR spectrum of the simple host molecule with that of the host-guest complex, and the 1 : 1 stoichiometry were further confirmed by the Job's method of continuous variation. From the results, we observed the binding constant (Ka) values of DPM3/DPM4 with various tested anions in the range of 516.07 M-1 to 63789.81 M-1, depending upon the nature/shape/size of the anions. Moreover, the anion-π interactions were confirmed by the partial 1H-NMR spectral data, and further supported by the literature reported systems. The authors hope that such types of valued receptors will be benefitted in future for the recognizing/binding of a variety of biologically important anions.

Improvement in Radiative Efficiency Via Intramolecular Charge Transfer in ortho-Carboranyl Luminophores Modified with Functionalized Biphenyls

In this study, we found that the electronic effects of the functional groups on aromatic units attached to o-carboranyl species can enhance the efficiency of intramolecular charge transfer (ICT)-based radiative decay processes. Six o-carboranyl-based luminophores having attached functionalized biphenyl groups with CF₃, F, H, CH₃, C(CH₃)₃, and OCH₃ substituents were prepared and fully characterized by multinuclear magnetic resonance spectroscopy. In addition, their molecular structures were determined by single-crystal X-ray diffractometry, which revealed that the distortion of the biphenyl rings and the geometries around the o-carborane cages were similar. All compounds exhibited ICT-based emissions in the rigid state (solution at 77 K and film). Intriguingly, the quantum efficiencies (Φ_em) of five compounds (that of the group with CF₃ could not be measured because of its extremely weak emissions) in the film state increased gradually as the electron-donating power of the terminal functional group modifying the biphenyl moiety increased. Furthermore, the nonradiative decay constants (k_nr) for the group with OCH₃ were estimated to be one-tenth of those for the group with F, whereas the radiative decay constants (k_r) for the five compounds were similar. The dipole moments (μ) calculated for the optimized first excited state (S₁) structures gradually increased, from that of the group with CF₃ to that of the group with OCH₃, implying that the inhomogeneity of the molecular charge distribution was enhanced by electron donation. The electron-rich environment formed as a result of electron donation led to efficient charge transfer to the excited state. Both experimental and theoretical findings revealed that the electronic environment of the aromatic moiety in o-carboranyl luminophores can be controlled to accelerate or interrupt the ICT process in the radiative decay of excited states.

Recent Progress in the Rational Design of Biothiol-Responsive Fluorescent Probes

Biothiols such as cysteine, homocysteine, and glutathione play significant roles in important biological activities, and their abnormal concentrations have been found to be closely associated with certain diseases, making their detection a critical task. To this end, fluorescent probes have become increasingly popular due to their numerous advantages, including easy handling, desirable spatiotemporal resolution, high sensitivity, fast response, and favorable biocompatibility. As a result, intensive research has been conducted to create fluorescent probes for the detection and imaging of biothiols. This brief review summarizes recent advances in the field of biothiol-responsive fluorescent probes, with an emphasis on rational probe design, including the reaction mechanism, discriminating detection, reversible detection, and specific detection. Furthermore, the challenges and prospects of fluorescence probes for biothiols are also outlined.

Utilization of photo-luminescent technique toward viscosity detection in the liquid food system with triphenylamine-michaelitic acid molecular sensor

A noninvasive and effective viscosity inspection method is expected to ease the burden of continued increased health problems caused by liquid food safety. In this study, we proposed the viscosity of the liquid food micro-environment as a marker and further developed a versatile optical sensor, DPTMDD, for monitoring liquid food micro-environmental viscosity alterations. This sensor was strategically constructed by the triphenylamine-thiophene derivate and michaelitic acid, rotatable conjugate structure was utilized as the recognition site. The molecular sensor was synthesized in a one-step facile way, and DPTMDD displayed a longer emission wavelength (592 nm), low detection limit (1.419 cP), and larger Stokes shift (193.7 nm in glycerol and 177.8 nm in water) with narrower energy band, endowing the sensor with the capacity of achieving high signal-to-noise ratio imaging. Meanwhile, DPTMDD exhibits high adaptability, selectivity, sensitivity, and good photo-stability in various liquid foods, bright fluorescent signal (37.5-fold) of DPTMDD is specifically activated in the high viscosity media. Thickening efficiencies can be identified as well. More importantly, the viscosity fluctuations during the metamorphic stages of liquid foods are also screened through in situ monitoring. We expected that this unique strategy will reinvigorate the continued perfection of liquid food safety investigation systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05699-y.

An environmentally insensitive fluorescent probe for G4 DNA detection: Design, synthesis, and mechanism studies

G4 DNA structure highly localized to functionally important sites within the human genome, has been identified as a biomarker for regulation of multiple biological processes. Identification G4-responsive fluorescence probes has broad application prospects for addressing G4 biological functions, as well as developing of new families of anticancer drugs. However, some currently designed G4 DNA probes may suffer from serious solvent-dependent effect, and cause unspecific fluorescence that masks the specific signal from G4 DNA. Herein, with a bulky imidazole-cored molecular rotor fusing in D-A building block of carbazole-pyridinium, we constructed a new probe ACPS. This new probe with desirable environmentally insensitive property exhibited a "fluorescence-off" state in various polarity solvents. In the presence of G4 DNA, the intra-molecular rotations would be restricted, triggering intense fluorescence enhancement. Especially, probe ACPS bound to G4 DNA structures with superior selectivity, exhibiting much weaker fluorescence response in the presence of non-G4 DNA structures. This probe was also able to realize fluorescence visualization in cell imaging. Collectively, the probe design strategy eliminates the background fluorescence caused by uncontrollable environmental polarity change, thereby achieving high-fidelity sensing G4 DNA structures in complicated systems.

Molecular Pincers Using a Combination of N-H and C-H Donors for Anion Binding

A naphthalene imide (1) and a naphthalene (2) bearing two pyrrole units have been synthesized, respectively, as anion receptors. It was revealed by ¹H NMR spectral studies carried out in CD₃CN that receptors 1 and 2 bind various anions via hydrogen bonds using both C-H and N-H donors. Compared with receptor 2, receptor 1 shows higher affinity for the test anions because of the enhanced acidity of its pyrrole NH and naphthalene CH hydrogens by the electron-withdrawing imide substituent. Molecular mechanics computations demonstrate that the receptors contact the halide anions via only one of the two respective available N-H and C-H donors whereas they use all four donors for binding of the oxyanions such as dihydrogen phosphate and hydrogen pyrophosphate. Receptor 1, a push-pull conjugated system, displays a strong fluorescence centered at 625 nm, while receptor 2 exhibits an emission with a maximum peak at 408 nm. In contrast, upon exposure of receptors 1 and 2 to the anions in question, their fluorescence was noticeably quenched particularly with relatively basic anions including F^-, H₂PO₄^-, HP₂O₇^3-, and HCO₃^-.

The arylvinylpyrimidine scaffold: a tunable platform for luminescent and optical materials

The incorporation of electron-withdrawing pyrimidine rings within π-extended systems allows access to a wide variety of fluorescent push-pull molecules that display emission properties highly sensitive to external stimuli. A suitable design of these compounds leads to interesting materials for a variety of optoelectronic applications. In this context, a vast number of arylvinylpyrimidine-based chromophores have been extensively studied during the last two decades. Along with the main synthetic pathways, this review summarizes the photophysical features of these active compounds having great potential and their most important applications as sensors and luminescence materials.

Selective Recognition and Reversible “Turn-Off” Fluorescence Sensing of Acetate (CH3COO−) Anion at Ppb Level Using a Simple Quinizarin Fluorescent Dye

A simple and cost-effective optical sensing system based on quinizarin fluorescent dye (QZ) for the selective and reversible sensing of CH3COO− anions is reported. The anion binding affinity of QZ towards different anions was monitored using electronic absorption and fluorescence emission titration studies in DMSO. The UV-visible absorption spectrum of QZ showed a decrease in the intensity of the characteristic absorption peaks at λ = 280, 323, and 475 nm, while a new peak appeared at λ = 586 nm after the addition of CH3COO− anions. Similarly, the initial strong emission intensity of QZ was attenuated following titration with CH3COO− anions. Notably, similar titration using other anions, such as F−, Cl−, I−, NO3−, NO2−, and H2PO4-, caused no observable changes in both absorption and emission spectra. The selective sensing of CH3COO− anions was also reflected by a sharp visual color change from bright green to faint green under room light. Further, the binding was found to be reversible, and this makes QZ a potential optical and colorimetric sensor for selective, reversible, and ppb-level detection of CH3COO− anions in a DMSO medium.

Imidazolium-Modified Bispyrene-Based Fluorescent Aggregates for Discrimination of Multiple Anions in Aqueous Solution

A great number of anions exist in biological systems and natural environment, and are highly relevant to human health and environment quality. It is necessary to develop simple and effective sensors to differentiate and identify those similar or different anions. Here, an imidazolium-modified bispyrene-based fluorescent amphiphilic probe DPyDIM was synthesized and its aggregates were applied to detect and discriminate various anions. The fluorescent aggregates exhibit ratiometric responses to different types of anions. Moreover, the ratiometric responses to different types of anions are featured with multiple-wavelength cross-reactivity. The collection of fluorescence variation at four typical wavelengths can generate distinct recognition patterns to specific anions. The heat map and principal component analysis results verify that this single fluorescent sensor system can effectively and sensitively identify 16 kinds of anions that belong to phosphorus-containing, sulfur-containing anions, and anionic surfactants. The cross-reactive sensing of the amphiphilic fluorescent aggregates was attributed to the different influences on the aggregation behaviors of the probes by different anions. The present work provides a promising strategy for effective detection and discrimination of multiple anions by employing dynamic fluorescent aggregates as a sensing platform.

A benzothiazole-based dual reaction site fluorescent probe for the selective detection of hydrazine in water and live cells

As hydrazine is an environmental pollutant and highly toxic to living organisms, selective and rapid detection is highly needed for the benefit of living organisms as well as the environment. Here, we first introduced a novel benzothiazole conjugated methyldicyanovinyl coumarin probe BTC, with dual recognition sites for hydrazine detection. The incorporation of the methyldicyanovinyl group into the benzocoumarin fluorophore increased the electrophilicity of the lactone ring of the probe BTC facilitating the nucleophilic attack of hydrazine and rapid (within 1 min, low detection limit = 1.7 nM) turn-on sky blue fluorescence with 700-fold fluorescence intensity enhancement was observed via hydrazine-induced lactone ring-opening followed by selective cleavage of the dicyanovinyl group. According to the literature, dicyanovinyl group assisted lactone ring opening has revealed the possibility of hydrazine recognition with a large Stokes shift (140 nm) and a high fluorescence quantum yield (0.67). Here, the DFT study and practical applications of the probe BTC in different water samples have been presented. The probe BTC was also successfully applied for the detection of hydrazine in the vapor phase using paper strips and in live MDA-MB 231 cells.

Polymeric agents for activatable fluorescence, self-luminescence and photoacoustic imaging

Numerous polymeric agents have been widely applied in biology and medicine by virtue of the facile chemical modification, feasible nano-engineering approaches and fine-tuned pharmacokinetics. To endow polymeric imaging agents with ability to monitor and measure subtle molecular or cellular alterations at diseased sites, activatable polymeric probes that can elicit signal changes in response to biomolecular interactions or the analytes of interest have to be developed. Herein, this review aims to provide a systemic interpretation and summarization of the design methodology and imaging utility of recently emerged activatable polymeric probes. An introduction of activatable probes allowing for precise imaging and classification of polymeric imaging agents is reported first. Then, we give a detailed discussion of the contemporary design approaches toward activatable polymeric probes in diverse imaging modes for the detection of various stimuli and their imaging applications. Finally, current challenges and future advances are discussed and highlighted.

A New Ratiometric Design Strategy Based on Modulation of π-Conjugation Unit for Developing Fluorescent Probe and Imaging of Cellular Peroxynitrite

Ratiometric fluorescent probes could effectively offset the changes of the autofluorescence and compartmental localization. FRET, ICT, etc. are the common strategies to design probes for biosensing, but these strategies have some deficiencies. Here, we proposed a new design strategy based on π-conjugation modulation, giving two different emission bands in the absence and presence of the target. The new fluorescence probe named Rhod-DCM-B was rationally designed and synthesized, which displayed a fluorescence emission peak at 670 nm because the electron cloud focuses on the conjugated DCM unit. With the addition of ONOO^-, the fluorescence emission at 570 nm increased, accompanied by the decrease of fluorescence emission at 670 nm, showing a ratiometric signal change attributed to the opened spirane structure making the electron cloud concentrated on the xanthene core. The mechanism is well confirmed by MS and DFT calculations. Rhod-DCM-B exhibited outstanding sensitivity and excellent selectivity toward ONOO^-. Moreover, Rhod-DCM-B was effectively employed to determine endogenous and exogenous ONOO^- in living cells. As a marker for inflammation and drug-induced liver injury (DILI) process, ONOO^- in vivo was successfully monitored by Rhod-DCM-B and presented a dramatic ratiometric response.

Chemical Design of Activatable Photoacoustic Probes for Precise Biomedical Applications

Photoacoustic (PA) imaging technology, a three-dimensional hybrid imaging modality that integrates the advantage of optical and acoustic imaging, has great application prospects in molecular imaging due to its high imaging depth and resolution. To endow PA imaging with the ability for real-time molecular visualization and precise biomedical diagnosis, numerous activatable molecular PA probes which can specifically alter their PA intensities upon reacting with the targets or biological events of interest have been developed. This review highlights the recent developments of activatable PA probes for precise biomedical applications including molecular detection of the biotargets and imaging of the biological events. First, the generation mechanism of PA signals will be given, followed by a brief introduction to contrast agents used for PA probe design. Then we will particularly summarize the general design principles for the alteration of PA signals and activatable strategies for developing precise PA probes. Furthermore, we will give a detailed discussion of activatable PA probes in molecular detection and biomedical imaging applications in living systems. At last, the current challenges and outlooks of future PA probes will be discussed. We hope that this review will stimulate new ideas to explore the potentials of activatable PA probes for precise biomedical applications in the future.

Analyte Interactions with Oxoporphyrinogen Derivatives: Computational Aspects

Abstract:

The binding of anions by highly-coloured chromophore compounds is of interest from the point-of-view of the development of optical sensors for analyte species. In this review, we have summarised our work on the interactions between oxoporphyrinogen type host compounds and different analyte species using computational methods. The origin of our interest in sensing using oxoporphyrinogens stems from an initial finding involving anion-host interactions involving a conjugated oxoporphyrinogen molecule. This review starts from that point, introducing some additional exemplary anion binding data, which is then elaborated to include descriptions of our synthesis work towards multitopic and ion pair interactions. In all the projects, we have consulted computational data on host structure and host-guest complexes in order to obtain information about the interactions occurring during complexation. Density functional theory and molecular dynamics simulations have been extensively used for these purposes. Oxoporphyrinogens are highly colored synthetically flexible compounds whose interactions with anions, ion pairs, and other species have been modelled using computational methods.

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