A novel ratiometric and reversible fluorescence probe with a large Stokes shift for Cu2+ based on a new clamp-on unit

Xylan derived fluorescence carbon dots composite with cotton cellulose paper as 'turn-off' fluorescence platform for sensitive and selective detection Cu2+ in real samples

The pollution of heavy metals such as Cu2+ is still serious and the discharge of sewage of Cu2+ will cause damage to soil environment and human health. Herein, a biomass-based solid-state fluorescence detection platform (CPU-CDs) was developed as fluorescent sensor for detection Cu2+ via fluorescence and colorimetric dual-model methods in real time. CPU-CDs was composed of xylan-derived CDs (U-CDs) and cotton cellulose paper, which exhibiting good reusability, non-toxicity, excellent fluorescence characteristics and high biocompatibility. Further, CPU-CDs displayed high effectiveness and sensitivity for Cu2+ with the detection limit as low as 0.14 μM, which was well below U.S. EPA safety levels (20 μM). Practical application indicated that CPU-CDs could achieve precision response of Cu2+ change in real environment water samples with good recovery range of 90 %-119 %. This strategy demonstrated a promising biomass solid-state fluorescence sensor for Cu2+ detection for water treatment research, which is of great significance in dealing with water pollution caused by heavy metal ions.

Poly(3-amino-carbazole) derivatives containing 1,10-phenanthroline and 8-hydroxyquinoline ligands: Synthesis, properties and application as ion sensors

As we know, excessive metal ions can even damage human health. Herein, two novel kinds of fluorescent sensing materials Poly(3-amino-carbazole) derivatives containing 1,10-phenanthroline and 8-hydroxyquinoline were synthesized and further applied to fluorescence detection for ions. The results show that Ni²⁺, Cu²⁺, and Pd²⁺ have excellent quenching effects on the fluorescence of Poly[9-(1,10-phenanthroline-2-yl)-9H-carbazol-3-amine] (PPNC), the LOD for these ions reaches 5.2 nM, 12.7 nM, 33.5 nM respectively. In the process of ion response, there is no shift of UV absorption peak, combined with IR spectra and theoretical calculation simulation, the quenching is considered to be caused by the coordination between metal ions and the second amine (-NH-) or 1,10-phenanthroline ligand of PPNC, which leads to the charge transfer from ligands to metal ions. In addition, an acid test was done for PPNC to verify and detect the presence of secondary amine (-NH-), and the results show that PPNC has good acid sensing ability which also supports the secondary amine (-NH-) structure. Finally, the paper test was performed on PPNC, indicating that PPNC has the potential for visual application.

The Application of Microwaves, Ultrasounds, and Their Combination in the Synthesis of Nitrogen-Containing Bicyclic Heterocycles

The use of alternative energy sources, such as microwaves (MW) or ultrasounds (US), and their mutual cross-combination have been widely described in the literature in the development of new synthetic methodologies in organic and medicinal chemistry. In this review, our attention is focused on representative examples, reported in the literature in the year range 2013-2023 of selected N-containing bicyclic heterocycles, with the aim to highlight the advantages of microwave- and ultrasound-assisted organic synthesis.

Fluorescent Mechanism of a Highly Selective Probe for Copper(II) Detection: A Theoretical Study

A highly selective probe for copper(II) detection based on the dansyl group was theoretically studied by means of (time-dependent) density functional theory. The calculated results indicated that the oscillator strength of the fluorescent process for the probe molecule is considerably large, but the counterpart of its copper(II) complex is nearly zero; therefore, the predicted radiative rate k_r of the probe is several orders of magnitude larger than that of its complex; however, the predicted internal conversion rate k_ic of both the probe and its complex is of the same order of magnitude. In addition, the simulated intersystem crossing rate k_isc of the complex is much greater than that of the probe due to the effect of heavy atom from the copper atom in the complex. Based on the above information, the calculated fluorescence quantum yield of the probe is 0.16% and that of the complex becomes 10^-6%, which implies that the first excited state of the probe is bright state and that of the complex is dark state. For the complex, the hole-electron pair analysis indicates that the process of S₀ → S₁ belongs to metal-to-ligand charge transfer; its density-of-state diagram visually illustrates that the highest occupied molecular orbital (HOMO) contains the ingredient of the s orbital from the copper atom, which decreases the frontier orbital energy level and the overlap integral of HOMO and LUMO.

A Ratiometric Selective Fluorescent Probe Derived from Pyrene for Cu2+ Detection

A novel ratiometric Cu2+-selective probe was rationally constructed based on pyrene derivative. Compared to other tested metal ions, the probe presented the selective recognition for Cu2+ which could be detected by a significant turn-on fluorescent response at 393 nm and 415 nm. Under the optimized conditions, a detection limit of 0.16 μM Cu2+ in aqueous media was found. Besides this, a 1:1 metal–ligand complex was confirmed by MS spectra and Job’s plot experiment, and the binding mode was also studied by 1H NMR experiment. Meanwhile, the fluorescence imaging in living cells was performed to detect Cu2+ with satisfactory results.

A salicylaldehyde benzoyl hydrazone based near-infrared probe for copper(ii) and its bioimaging applications

Developing highly sensitive and selective methods for Cu²⁺ detection in living systems is of great significance in clinical copper-related disease diagnosis. In this work, a near infrared (NIR) fluorescent probe, CySBH, with a salicylaldehyde benzoyl hydrazone group as a selective and sensitive receptor for Cu²⁺ was designed and synthesized. The specific coordination of the salicylaldehyde benzoyl hydrazone group in CySBH with Cu²⁺ can induce a distinct quench of the fluorescence intensity, allowing for real-time tracking of Cu²⁺. We have demonstrated that CySBH could rapidly recognize Cu²⁺ with good selectivity and high sensitivity. Moreover, on the basis of low cell cytotoxicity, the probe was used to visualize Cu²⁺ in two cell lines by fluorescence imaging. Furthermore, CySBH can also be used to monitor Cu²⁺in vivo due to its NIR emission properties. These overall results illustrate that the NIR fluorescent probe CySBH provides a novel approach for the selective and sensitive monitoring of Cu²⁺ in living systems.

A near infrared fluorescent probe utilizing the salicylaldehyde benzoyl hydrazone group as the Cu²⁺ receptor was developed and used to selectively and sensitively monitor Cu²⁺ in living systems.

An α-naphtholphthalein-derived colorimetric fluorescent chemoprobe for the portable and visualized monitoring of Hg2+ by the hydrolysis mechanism

An ɑ-naphtholphthalein-derived colorimetric fluorescent chemoprobe was elaborately designed for the portable and visual monitoring of Hg2+ in environmental and biological samples.

Two-dimensional nano-layered materials as multi-responsive chemosensors constructed by carbazole- and fluorene-based polyaniline-like derivatives

The development of multi-responsive chemosensors has a bright application prospect in environmental monitoring and biological diagnosis. In this paper, we report two kinds of fluorescent polyaniline-like derivatives containing of carbazole or fluorene moieties with two-dimensional (2D) nano-layered structure and their applications in the detection of Al³⁺, Fe³⁺, Cu²⁺ and HCl in different environments. Through the analysis of the structure and properties of these two 2D materials, we find that the prepared (Poly(9,9'-(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(9H-carbazol-3-amine))) PDFCA material performs excellent sensing properties for above analytes. Relevant density functional theory (DFT) calculation further confirms the potential application of 2D nano-layered PDFCA material in sensing field. This study presents that 2D nano-layered PDFCA material is considerably competitive in the development of multi-responsive chemosensors, and it will greatly accelerate the research of 2D polymer materials.

White light employing luminescent engineered large (mega) Stokes shift molecules: a review

Large (mega) Stokes shift molecules have shown great potential in white light emission for optoelectronic applications, such as flat panel display technology, light-emitting diodes, photosensitizers, molecular probes, cellular and bioimaging, and other applications. This review aims to summarize recent developments of white light generation that incorporate a large Stokes shift component, key approaches to designing large Stokes shift molecules, perspectives on future opportunities, and remaining challenges confronting this emerging research field. After a brief introduction of feasible pathways in generating white light, exemplifications of large Stokes shift molecules as white light candidates from organic and inorganic-based materials are illustrated. Various possible ways to design such molecules have been revealed by integrating the photophysical mechanisms that are essential to produce red-shifted emission upon photoexcitation, such as excited state intramolecular proton transfer (ESIPT), intramolecular charge transfer (ICT), excited state geometrical relaxation or structural deformation, aggregation-induced emission (AIE) alongside the different formations of aggregates, interplay between monomer and excimer emission, host-guest interaction, and lastly metal to ligand charge transfer (MLCT) via harvesting triplet state. Furthermore, previously reported fluorescent materials are described and categorized based on luminescence behaviors on account of the Stokes shifts value. This review will serve as a rationalized introduction and reference for researchers who are interested in exploring large or mega Stokes shift molecules, and will motivate new strategies along with instigation of persistent efforts in this prominent subject area with great avenues.

Fluorescent sensing film decorated with ratiometric probe for visual and recyclable monitoring of Cu2

Specifically, visually, and quantitatively monitor copper ion (Cu²⁺) is critical in the area of biological and environmental detection. Herein, a ratiometric fluorescent probe with benzoxazole appended xanthenes skeleton was constructed and further employed to monitor Cu²⁺ in Hela cells, real water samples, and test strips. An easily distinguishable colorimetric (colorless to red) and fluorescence (green to red) change could be observed by naked eye under the portable UV lamp (365 nm) and the changes could be recovered by adding S^2-. Furthermore, electrospinning technique was employed to fabricate a probe composited fluorescent sensing film (PMMA) for realizing the visual and recyclable monitoring of Cu²⁺, indicating that the probe-composited fluorescent sensing film has great potential for on-site and naked-eye detection of Cu²⁺ in practical.

Two Novel Fluorescent Probes as Systematic Sensors for Multiple Metal Ions: Focus on Detection of Hg2

Many precedents prove that fluorescent probes are promising candidates for detection of metal ions in the environment and biological systems. Herein, two novel photoinduced electron transfer (PET)-based fluorescent probes, CH 3 -R6G and CN-R6G, were rationally synthesized by incorporating a triazolyl benzaldehyde moiety into the rhodamine 6G fluorophore. The optical properties of these probes were studied using an ultraviolet-visible (UV-vis) absorption spectrophotometer and a fluorescence spectrophotometer. Through the analysis of the test results, it is concluded that the selectivity and sensitivity of these two probes to Hg2+ are better than to other metal ions (Ag+, Al3+, Ba2+, Cd2+, Co3+, Cu2+, Cr3+, Fe3+, Ga2+, K+, Mg2+, Na+, Ni2+, Pb2+, and Zn2+). According to the standard curve diagram, the detection limits of CH 3 -R6G and CN-R6G were determined to be 1.34 × 10-8 and 1.56 × 10-8 M, respectively. Reaction of the probes with Hg2+ resulted in a color change of the solution from colorless to pink. The corresponding molecular geometric configuration, orbital electron distribution, and orbital energy of these two compounds were predicted by density functional theory (DFT). The two probes CH 3 -R6G and CN-R6G have been successfully used for imaging Hg2+ in live breast cancer cells, thereby indicating their great potential for the micro-detection of Hg2+ in vivo.

A dual-functional probe for sensing pH change and ratiometric detection of Cu2

A series of benzothiazole-based compounds were synthesized and characterized. Among them, probe Z showed significant dual-functional performance which was capable of sensing pH change and Cu²⁺. Probe Z displayed fluorescent turn-on under alkaline conditions due to deprotonation of the hydroxyl group along with the obviously color change from colorless to mint green. Interestingly, it further achieved in ratiometric detection of Cu²⁺ through absorbance or fluorescence signals in strong alkaline condition. The limit of detection was calculated correspondingly as 0.37 μM and 1.35 μM, respectively. Especially, the combination of the XNOR and INHIBIT logic gates could be used to confirm that one medium was in neutrality or alkalinity condition. Moreover, Z was successfully used in real water samples and test paper for fast identification of Cu²⁺, respectively.

Development of highly efficient chemosensors for Cu2+ and N2H4 detection based on 2D polyaniline derivatives by template-free chemical polymerization method

Chemosensors play an important role in environmental protection, medical diagnosis and energy conservation. Although polyaniline and its derivatives and two-dimensional (2D) materials have been applied as chemosensors in many reports, the concept of two-dimensional (2D) polyaniline derivatives has not been achieved in chemosensors. Here, two kinds of two-dimensional (2D) polyaniline derivatives are designed and synthesized by template-free chemical polymerization. It can be found that these two two-dimensional (2D) chemosensors exhibit high selectivity and sensitivity to Cu²⁺ and N₂H₄. Moreover, it is noteworthy that one of the two-dimensional materials can achieve the limit of detection (LOD) of 45 nM and 8 nM for Cu²⁺ and N₂H₄, respectively. Especially, these results imply that this two-dimensional polyaniline derivative is promising as the chemosensor in sensing field.

A nopinone based multi-functional probe for colorimetric detection of Cu2+ and ratiometric detection of Ag. Photochem Photobiol Sci 2020;19:49-55. [PMID: 31793618 DOI: 10.1039/c9pp00297a]

A dual-signal probe PPN based on the natural β-pinene derivative nopinone was synthesized for the colorimetric detection of Cu2+ and ratiometric detection of Ag+. Upon the addition of Ag+, a significant fluorescence change from blue to green was observed with a low detection limit (0.86 μM). However, upon the addition of Cu2+, a significant color change from colorless to yellow was observed with a low detection limit (0.56 μM). The novel probe PPN was applied as a probe for the colorimetric detection of Cu2+ and ratiometric detection of Ag+ with a high selectivity, good sensitivity and fast response time. The detection mechanisms of probe PPN for Cu2+/Ag+ were confirmed by 1H NMR and HRMS-ESI. Besides, probe PPN could sense Cu2+/Ag+ on test strips. Additionally, probe PPN could be applied to quantitatively detect the concentration of Ag+ in water samples and image Ag+ in living cells.

A multiple fluorescein-based turn-on fluorophore (FHCS) identified for simultaneous determination and living imaging of toxic Al3+ and Zn2+ by improved Stokes shift

A multiple turn-on fluorophore (FHCS), combining fluorescein, hydrazone, cyanuric chloride and salicylaldehyde chromone into a molecule, was identified and developed based on density functional theoretical calculation. It was expected that FHCS could express exclusive fluorescent signals and improved Stokes shifts when chelating Al³⁺ or Zn²⁺. After it was synthesized and characterized in detail, it was noted that FHCS could turn-on fluorescently discriminate trace Al³⁺ and Zn²⁺ under the optimized conditions, i.e., from no-fluorescence to strong blue fluorescence for Al³⁺ and to green fluorescence for Zn²⁺ with low detection limits of 5.37 × 10^-8 M and 7.90 × 10^-8 M respectively. Owing to its low toxicity, FHCS was successfully applied for quantitative determination of Al³⁺ and Zn²⁺ in natural aqueous samples and toxicity evaluation of Al³⁺ and Zn²⁺ in living cells and bio-tissues with excellent linear relationships. The action mechanisms for FHCS with Al³⁺ and Zn²⁺ were confirmed to form stable 5-member-co-6-member condensed rings between Al³⁺/Zn²⁺ and N/O atoms in FHCS by both theoretic and experimental methods, which resulted in turn-on fluorescence with different dipolar moments and improved Stokes shifts.