An Imidazole-Functionalized Polyfluorene Derivative as Sensitive Fluorescent Probe for Metal Ions and Cyanide

Design and optimization of encapsulated sensor materials with diverse binding sites for efficient cyanide ion detection

Developing colorimetric and fluorimetric sensors with a new design strategy incorporates the same electron donor and acceptor units by changing the binding site by expecting different mechanisms. The sensors YS and RS have the D-π-A concept, having phenothiazine as an electron donor and benzothiazole as an electron acceptor for sensing cyanide ions in various spectral techniques. Both the sensors showed an efficient color change with cyanide ion in day light and UV light, which was confirmed by UV-vis and Fluorescence spectral analysis. The mechanism of sensing cyanide ion by the sensor YS via hydrogen bond formation followed by deprotonation and RS via nucleophilic addition reaction was confirmed with a 1H NMR, FT-IR and HRMS spectral studies. The detection limit was found to be 1.36 μM and 0.78 μM by UV-vis, 0.13 nM and 0.39 nM by fluorescence technique are for sensors YS and RS, which are significantly lower than the WHO criterion of 1.9 μM for cyanide ions in water used for drinking. Furthermore, the real-world application showed that the sensors could quantitatively identify the quantity of cyanide ion present in different types of water samples. Besides, the fabricated test strips make the sensors easy to utilize for detecting CN- in the field without the need for complicated devices. Also, the developed sensor-encapsulated Polysulfone (PSF) capsule kit effectively senses cyanide ion in water.

Development of a fluorescent scaffold by utilizing quercetin template for selective detection of Hg2+: Experimental and theoretical studies along with live cell imaging

Quercetin is an important antioxidant with high bioactivity and it has been used as SARS-CoV-2 inhibitor significantly. Quercetin, one of the most abundant flavonoids in nature, has been in the spot of numerous experimental and theoretical studies in the past decade due to its great biological and medicinal importance. But there have been limited instances of employing quercetin and its derivatives as a fluorescent framework for specific detection of various cations and anions in the chemosensing field. Therefore, we have developed a novel chemosensor based on quercetin coupled benzyl ethers (QBE) for selective detection of Hg2+ with "naked-eye" colorimetric and "turn-on" fluorometric response. Initially QBE itself exhibited very weak fluorescence with low quantum yield (Φ = 0.009) due to operating photoinduced electron transfer (PET) and inhibition of excited state intramolecular proton transfer (ESIPT) as well as intramolecular charge transfer (ICT) within the molecule. But in presence of Hg2+, QBE showed a sharp increase in fluorescence intensity by 18-fold at wavelength 444 nm with high quantum yield (Φ = 0.159) for the chelation-enhanced fluorescence (CHEF) with coordination of Hg2+, which hampers PET within the molecule. The strong binding affinity of QBE towards Hg2+ has been proved by lower detection limit at 8.47 µM and high binding constant value as 2 × 104 M-1. The binding mechanism has been verified by DFT study, Cyclic voltammograms and Jobs plot analysis. For the practical application, the binding selectivity of QBE with Hg2+ has been capitalized in physiological medium to detect intracellular Hg2+ levels in living plant tissue by using green gram seeds. Thus, employing QBE as a fluorescent chemosensor for the specific identification of Hg2+ will pave the way for a novel approach to simplifying the creation of various chemosensors based on quercetin backbone for the precise detection of various biologically significant analytes.

Tailored fluorophore design: Enhancing selectivity for cyanide ion sensing in water and food samples, and innovative device development

A rigid fluorophore unit of Julolidine/coumarin fused with an indolium-conjugated system was built for the immediate and effective recognition of cyanide ions in a 90 % aq. DMSO solution. The probes are capable of displaying better sensitivity/selectivity for the cyanide ion over a wide range of other interfering ions. The probe JI showed an instant colorimetric variation, whereas the modified probe JCI showed both colorimetric and fluorimetric variation with cyanide ion. The observed detection limit values indicated excellent sensitivity of the probe to the cyanide ion. HRMS and 1H NMR studies confirmed that the mechanism of detection of CN- is via the nucleophilic attack on the electron-deficient indolium moiety of the molecule. Moreover, the probes are well proficient in selective recognition of cyanide in various real time applications (test strips, electronic sensor kit, food and water sample analysis).

Single Organic Ligands Act as a Bifunctional Sensor for Subsequent Detection of Metal and Cyanide Ions, a Statistical Approach toward Coordination and Sensitivity

The detection of key ions in environmental samples has garnered significant attention in recent years in the pursuit of a cleaner environment for living organisms. Bifunctional and multifunctional sensors, as opposed to single-species sensors, have emerged as a rapidly developing field. Many reports in the literature have documented the use of bifunctional sensors for the subsequent detection of metal and cyanide ions. These sensors, consisting of simple organic ligands, form coordination compounds with transition metal ions, resulting in clear visible or fluorescent changes that facilitate detection. In some cases, a single polymeric material can act as a ligand and coordinate with metal ions, forming a complex that serves as a sensor for cyanide ion detection in biological and environmental samples through various mechanisms. Nitrogen is the most dominant coordinating site in these bifunctional sensors, with the sensitivity of the sensors being directly proportional to the denticities of ligands for metal ions, while for cyanide ions the sensitivity was found independent of the denticity of the ligands. This review covers the progress made in the field over the past fifteen years (2007-2022), with most ligands detecting copper (II) and cyanide ions, but with the capability to detect other metals such as iron, mercury, and cobalt as well.

The crystal structure of 2-carboxyl-4-nitroimidazole monohydrate, C4H5N3O5

C4H5N3O5, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 6.3017(7) Å, b = 6.9235(7) Å, c = 8.2333(8) Å, α =100.604(3)°, β = 90.862(4)°, γ = 108.102(4)°, V = 334.60(6) Å3, Z = 2, R gt (F) = 0.0616, wR ref (F 2) = 0.1414, T = 170.0 K.

3-Hydroxyflavone derivatives: promising scaffolds for fluorescent imaging in cells

As a typical class of excited-state intramolecular proton transfer (ESIPT) molecules, 3-hydroxyflavone derivatives (3HF, also known as flavonols) have received much attention recently. Thereinto, the role of hydrophobic microenvironment is significant importance in promoting the process and effects of ESIPT, which can be regulated by the solvents, the existence of metal ions and proteins rich with α-helix structures or the advanced DNA structures. Considering that plenty of biological macromolecules offer cellular hydrophobic microenvironment, enhancing the ESIPT effects and resulting in dual emission, 3HF could be a promising scaffold for the development of fluorescent imaging in cells. Furthermore, as the widespread occurance of compounds with biological activity in plants, 3HF derivatives are much more secure to be cellular diagnosis and treatment integrated fluorescent probes. In this review, multiple regulatory strategies for the fluorescence emission of 3HF derivatives have been collectively and comprehensively analyzed, including the solvent effects, metal chelation, interaction with proteins or DNAs, which would be beneficial for ESIPT-promoting or ESIPT-blocking processes and then enhance or control the fluorescence emission of 3HF effectively. We expect that this review would provide a new perspective to develop novel 3HF-based fluorescent sensors for imaging in cells and plants.

One-Step Assembly of Fluorescence-Based Cyanide Sensors from Inexpensive, Off-The-Shelf Materials

We report a simple and versatile approach to assemble sensitive and selective fluorescence “turn-on” sensors for cyanide by combining three off-the-shelf materials; namely fluorescent dye, 1-vinyl imidazole polymer, and cupric chloride. The cyanide-sensing species is a non-fluorescent fluorophore-polymer-Cu²⁺ complex; which forms as a result of the imidazole polymer’s ability to bind both fluorophore and fluorescence quencher (Cu²⁺). Cyanide removes Cu²⁺ from these complexes; thereby “turning-on” sensor fluorescence. These sensors are water-soluble and have a detection limit of ~2.5 μM (CN⁻) in water. Our ternary complex-based sensing approach also enables facile emission tuning; we demonstrate the convenient, synthesis-free preparation of blue and green-emitting sensors using distyrylbiphenyl and fluorescein fluorophores, respectively. Furthermore; these ternary complexes are easily immobilized using agarose to create cyanide-sensing hydrogels; which are then used in a simple; novel microdiffusion apparatus to achieve interference-free cyanide analysis of aqueous media. The present study provides an inexpensive approach for portable; interference-free cyanide detection.

Polysubstituted Imidazoles as LysoTracker Molecules: Their Synthesis via Iodine/H2O and Cell-Imaging Studies

An iodine-catalyzed, environmentally benign one-pot methodology has been developed for the synthesis of diverse substituted imidazoles. This transition-metal-free, aerobic, water-mediated cyclization reaction is operationally simple and works well with different amines or aldehydes by multiple C-N bond formations with satisfactory yield. The methodology is regioselective as well as scalable. These imidazole derivatives show excellent fluorescence properties both in the solid and solution phase, which is further extended to live-cell imaging. Due to the suitable fluorescence properties of these scaffolds, lysosome-directing groups are incorporated in two of these derivatized imidazoles to track intracellular lysosomes. Successfully, those molecules show bright blue fluorescence while detecting lysosomes in human or murine cells and can be considered to be rapid lysosome-staining probes.

Fluorescent chemosensors based on conjugated polymers with N-heterocyclic moieties: two decades of progress

A brief summary of representative fluorescent chemosensors based on conjugated polymers with N-heterocyclic moieties, followed by a discussion on the limitations and challenges of current systems, as well as possible future research directions.

Substituent effect on colorimetric detection of biologically and environmentally relevant anions: Insight in real-life applications

A new set of chromogenic anion receptors R1-R4 have been synthesized with a different substituent, including electron withdrawing (nitro moiety in R1), conjugated group (naphthyl in R2), and electron donating (methyl in R3), respectively. The receptors R1-R4 exhibited very good sensitivity towards the F^- and AcO^- anions in the DMSO. In addition, R1 showed selectivity towards H₂PO₄^- ions over other tested anions. R1 especially acted as an effective sensor for sodium salts of F^-, AcO^-, AsO₂^-, and AsO₄^2- ions in an aqueous medium due to the presence of two electron-withdrawing nitro substituents, which showed hydrogen bond donor tendency and acidity of the OH proton. This result indicates that R1 is highly capable of competing with an aqueous medium to detect anions without counter Na⁺ ion interference. Interestingly, R1 displays solvatochromic property in the presence of AcO^- ions in different aprotic solvents. Additionally, the receptor R1 shows high binding affinity towards AcO^- ions in the buffer medium (DMSO: HEPES, 9:1 v/v), which displayed remarkable colour change from pale yellow to blue with a large ∆λ_{red shift} of 170 nm. The CV studies reveal the deprotonation of the -NH proton upon interaction with the AcO^- ions. The receptor R1 is subjected to practical application to sense F^- and AsO₂^- ions using the test strip. In addition, the receptor R1 proves itself as a potential applicant for the detection of F^- ions quantitatively in commercially available mouthwash.

Visual detection of fluoride ion based on ICT mechanism

A novel chemosensor (H₃NTS) has been designed for a fast and accurate detection of F^- in acetonitrile medium. The UV-Vis, ¹H, ¹³C NMR experiments and computational calculations demonstrate that H₃NTS probe offers a potential colorimetric sensor for discriminating F^- among other relevant anions. The detection limit is as low as 6 μM and a reversible colorimetric switch could be devised by sequential addition of F^-/Ca²⁺. The promising application of H₃NTS is also confirmed in real examples where the concentration of F^- is a critical parameter, e.g., commercial toothpaste, paper strip and gel form analysis of samples.

Direct synthesis of 2,4,5-trisubstituted imidazoles from primary alcohols by diruthenium(ii) catalysts under aerobic conditions

A straightforward synthetic approach to 2,4,5-trisubstituted imidazoles from readily available primary alcohols using arene diruthenium(ii) catalysts has been described.

A Comparison of ACQ, AIE and AEE-Based Polymers Loaded on Polyurethane Foams as Sensors for Explosives Detection

An aggregation-caused quenching (ACQ)-active polymer (PF), an aggregation-induced emission (AIE)-active polymer (PFTPE) and an aggregation-enhanced emission (AEE)-active polymer (PTTPE) were synthesized by tetraphenylethane (TPE), fluorene and thiophene moieties. Polyurethane (PU) foams modified by PF, PFTPE and PTTPE, namely PU-PF, PU-PFTPE and PU-PTTPE, using ultrasonication-assisted method have been prepared. A comparative study of PU-PF, PU-PFTPE and PU-PTTPE for detection explosives had been performed, and significant fluorescence quenching was observed with the introduction of PA solutions. The as-prepared PU-PF, PU-PFTPE and PU-PTTPE sensors exhibited a superior sensitivity for PA solutions with different concentrations. Remarkably, PU-PF gave a quenching efficiency of 96.2%, higher than 93.5% for PU-PFTPE and 86.7% for PU-PTTPE at a PA concentration of 180 µg·mL⁻¹ in methanol, which was attributed to the effective energy transfer from the fluorophore (PF) to the nitro explosive (PA). This suggested that some ACQ polymers, applied to detect explosives, could afford better performances than AIE or AEE polymers through modification of structures and selection of adequate carriers. At the same time, these chemical sensors can be recycled many times.

Highly sensitive "turn-on" fluorescent chemical sensor for trace analysis of Cr3+ using electro-synthesized poly(N-(9-fluorenylmethoxycarbonyl)-l-histidine)

Trivalent chromium (Cr³⁺) can cause severely environment pollution, declining quality of edible agro-products in plants and animals, and human diseases. Poly(N-(9-fluorenylmethoxycarbonyl)-l-histidine) (PFLH) synthesized by the direct electro-polymerization of its corresponding commercially available monomer in both boron trifluoride diethyl etherate and dichloromethane mixed system. The "turn-on" type fluorescent sensor based on PFLH displayed high sensitivity and selectivity for Cr³⁺ detecting. The structure of PFLH was rationally proved by ¹H NMR spectra, FT-IR spectra, quantum chemical calculations, and its optical properties were characterized. The electro-synthesized PFLH exhibited a "turn-on" fluorescent response towards Cr³⁺, which was employed as a sensing platform for the "turn-on" fluorescent analysis of Cr³⁺ in a wide linear range from 5.1nM to 25μM with a low limit of detection as low as 1.7nM. The possible mechanism of fluorescent "turn-on" sensor based on PFLH for Cr³⁺ was proposed. The sensor displayed high sensitivity, good selectivity, satisfactory practicability, suggesting that PFLH has potential fluorescent application for "turn-on" sensing Cr³⁺ in agricultural environments and edible agro-products of plants and animals.

Design and application of a fluorogenic receptor for selective sensing of cations, small neutral molecules, and anions

An unprecedented single multi-analyte fluorogenic receptor, a sodium salt of N-(methyl-2-thiophenyl)-tyrosine (NaHTyrthio), is reported for the selective sensing of cations (Cu²⁺), small neutral molecules (nitrobenzene and aniline) and anions (F⁻) by variable spectral responses.

Studies on a multifunctional chromo-fluorogenic sensor for dual channel recognition of Zn2+ and CN− ions in aqueous media: mimicking multiple molecular logic gates and memory devices

A new effectual naphthalene-based azomethine receptor has been systematically designed and synthesized as a selective colorimetric and fluorescent chemosensor for dual channel detection of cations and anions in aqueous environments.

Pentafluorophenyl dipyrrin as probe for transition metal ion detection and bioremediation in Bacillus subtilis and Bacillus cereus

Recognition of transition metal ions and bioaccumulation in B. subtilis and B. cereus were examined using pentafluorophenyl dipyrrin probe.

Imidazole/benzimidazole-modified cyclotriphosphazenes as highly selective fluorescent probes for Cu2+: synthesis, configurational isomers, and crystal structures

We present a comprehensive work and discuss the fluoroprobe properties of synthesized compounds for copper ion detection with a stereochemical approach using X-ray crystallographic analysis results.

Fluorescence behaviour of an anthracene-BODIPY system affected by spin states of a dioxolene-cobalt centre

Dioxolene cobalt complexes, [Co(L)(TPA)]PF6 () and [Co(L)(Me3TPA)]PF6 (), were synthesized using a catechol with anthracene and boron-dipyrromethene (BODIPY), H2L, and tris(pyridin-2-ylmethyl)amine (TPA) or tris[(6-methylpyridin-2-yl)methyl]amine (Me3TPA) and characterised by UV-vis absorption, IR and NMR spectroscopy. Complexes and are a low-spin cobalt(iii) catecholate form and a high-spin cobalt(ii) semiquinonate form, respectively, in CH3CN at room temperature. The effect of the spin states of the dioxolene-cobalt centre on fluorescence was investigated in CH3CN at room temperature. The fluorescence intensity of was clearly lower than that of , although both complexes showed weaker fluorescence compared with that of H2L. The difference in the intensity between and is mainly due to the enhancement of nonradiative decay processes based on the stronger metal-ligand interactions for the cobalt(iii) catecholate form of compared with the cobalt(ii) semiquinonate form of .

Coordination-induced gelation of an l-glutamic acid Schiff base derivative: the anion effect and cyanide-specific selectivity

Three metallogels, ZnG, CuG and Zn-CuG, were prepared in the presence of specific anions, with their efficacy linked to the Hofmeister series. Importantly, Zn-CuG gel could fluorescently detect CN⁻ with specific selectivity.

A cyanide-selective colorimetric “naked-eye” and fluorescent chemosensor based on a diketopyrrolopyrrole–hydrazone conjugate and its use for the design of a molecular-scale logic device

A novel diketopyrrolopyrrole (DPP)–hydrazone based receptor was designed and synthesized as a selective fluorescent and colorimetric chemosensor for cyanide in aqueous media via deprotonation between the hydrazide moiety of the probe and cyanide.

A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes

N-(2,4-dinitrobenzylidene)-4-methoxyaniline (1), 4-(N,N-dimethylamine)-N-(2,4-dinitrobenzylidene)aniline (2), 2,4-dinitro-4'-methoxystilbene (3), and 2,4-dinitro-4'-(dimethylamino)stilbene (4) were synthesized and studied in dimethyl sulfoxide in a novel strategy as anionic chromogenic chemosensors. The color of the solutions of these compounds changed only in the presence of cyanide. The kinetic studies were performed with compounds 1-3 in an excess of cyanide. Higher second-order rate constant values were obtained for the compounds containing a methoxy group in relation to the compounds with a dimethylamino substituent, since the methoxy group donates electronic density to the 2,4-dinitrophenyl electron-accepting group less easily compared with the dimethylamino group. Stilbenes generally have greater structural rigidity than imines, facilitating the action of the substituents through the mesomeric effect. The data obtained indicate that the anion acts as a nucleophile, being responsible for CN bond breaking. The CC bridge is not broken in the stilbene dyes, but cyanide performs a nucleophilic attack on the 2,4-dinitrophenyl group.

Pyrene and imidazole functionalized luminescent bimetallic Ru(ii) terpyridine complexes as efficient optical chemosensors for cyanide in aqueous, organic and solid media

Luminescent bimetallic Ru(ii)-terpyridine complexes based on the pyrenyl-bis-phenylimidazole spacer as highly efficient sensors for cyanide in aqueous, organic and solid media are reported.

A pyrenesulfonyl-imidazolium derivative as a selective cyanide ion sensor in aqueous media

Unlocking of probe 2 with CN⁻ ions leads to its minimum detection limit of 0.5 μM (13 ppb).

Cationic polythiophene for specific detection of cyanide ions in water using fluorometric technique

A new fluorometric cyanide sensor using cationic polythiophene exhibits high sensitivity, selectivity with a low detection limit (4.4 ppb) in water.

Pyrene-biimidazole based Ru(ii) and Os(ii) complexes as highly efficient probes for the visible and near-infrared detection of cyanide in aqueous media

Pyrenyl-biimidazole based Ru(ii) and Os(ii) complexes are used as highly efficient cyanide sensors in aqueous media.

The utilization of post-synthetic modification in opto-electronic polymers: an effective complementary approach but not a competitive one to the traditional direct polymerization process

By presenting some typical examples, the recent progress of opto-electronic polymers is reviewed, which were only accessible from the post-synthetic modification strategy.