Solvent-dependent chromogenic sensing for Cu2+ and fluorogenic sensing for Zn2+ and Al3+: a multifunctional chemosensor with dual-mode

2-hydroxy-1- Naphthaldehyde Based Colorimetric Probe for the Simultaneous Detection of Bivalent Copper and Nickel with High Sensitivity and Selectivity

A neoteric colorimetric probe based on 2-hydroxy-1-naphthaldehyde (PMB3) was designed and synthesized for the real-time as well as on-site naked-eye detection of Cu2+/Ni2+ ions. Various physicochemical methods were employed to characterize the probe, and its colorimetric response to different metal ions was meticulously investigated. The probe, PMB3, exhibited a sensitive colorimetric response to Cu2+/Ni2+ ions among other competing metal ions, culminating in a prominent colour change from colourless to yellow. The stoichiometry of the ligand metal complexes was ascertained to be in a 1:1 ratio using Job's plot analysis, which was further corroborated by ESI-MS data. With detection limits of 4.56 µM for Cu2+ and 2.68 µM for Ni2+, the method was effectively extended to real sample analysis, ensuring propitious results that closely aligned with the actual values.

a Versatile Schiff Base Chemosensor for the Determination of Trace Co2+, Ni2+, Cu2+, and Zn2+ in the Water and Its Bioimaging Applications

In this work, a simple and versatile Schiff base chemosensor (L) was developed for the detection of four adjacent row 4 metal ions (Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) through colorimetric or fluorescent analyses. L could recognize the target ions in solutions containing a wide range of other cations and anions. The recognition mechanisms were verified with a Job's plot, HR-MS assays, and ¹H NMR titration experiments. Then, L was employed to develop colorimetric test strips and TLC plates for Co²⁺. Meanwhile, L was capable of quantitatively measuring the amount of target ions in tap water and river water samples. Notably, L was used for imaging Zn²⁺ in HepG2 cells, zebrafish, and tumor-bearing mice, which demonstrated its potential biological applications. Therefore, L can probably serve as a versatile tool for the detection of the target metal ions in environmental and biological applications.

A reversible and efficient probe for dual mode recognition of Al3+ and Cu2+ with logic gate behaviour: Crystal structure, theoretical and in-vivo bio-imaging investigations

This work presents the synthesis, characterization, crystal structure and spectroscopic investigations of isophthalohydrazide based probe. Among various tested metal ions, the probe selectively detects Al³⁺ and Cu²⁺ in aqueous ethanol via fluorometric and colorimetric methods, respectively. It displays a fluorescence "turn-on" response with Al³⁺ and visual colour change from colourless to yellow with Cu²⁺. Sensing mechanism is explored with UV-Vis, fluorescence spectroscopy and ¹H NMR titration, and confirmed with computational results. Suppression of CN isomerization and photo-induced electron transfer (PET) along with chelation enhanced fluorescence emission (CHEF) result in "turn-on" fluorescence with Al³⁺ while ligand to metal charge transfer (LMCT) accounts for visual colour change with Cu²⁺. Job's plot and HRMS confirm 1:2 (L:M) stoichiometry. The probe also exhibits efficient reversibility and reproducibility with EDTA which are successfully mimicked with combinatorial logic gate and truth table. Additionally, solid state applications and bio-imaging investigation on gut tissue of Drosophila 3rd instar larvae are performed.

Solvent-Regulated Fluorimetric Differentiation of Al3+ and Zn2+ Using an AIE-Active Single Sensor

The absence of d-orbital electrons or presence of full-filled d-orbital electrons in metal ions is a well-known Achilles' heel problem for the detection of these metal ions by a simple UV-visible study. For this reason, detection of metal ions such as Al³⁺ with no d-orbital electrons or Zn²⁺ with filled d-orbital electrons is a challenging task. Herein, we report a 2-naphthol-based fluorescent probe [1-((E)-((E)-(5-bromo-2-hydroxybenzylidene)hydrazono)methyl)naphthalen-2-ol] (H₂L) that has been used to sense and discriminate Al³⁺ and Zn²⁺ via solvent regulation. The probe exhibits excellent selectivity and swift sensitivity toward Al³⁺ in MeOH-water (9:1, v/v) and toward Zn²⁺ in dimethyl sulfoxide (DMSO)-water (9:1, v/v) among various metal ions. The respective detection limit is found to be 9.78 and 3.65 μM. The sensing mechanism is attributed to multiple processes, viz., the inhibition of photo-induced electron transfer (PET) along with the introduction of chelation-enhanced emission (CHEF) and excited-state intramolecular proton transfer (ESIPT) inhibition, which are experimentally well verified by UV-vis absorption spectroscopy, emission spectroscopy, and NMR spectroscopy. The probe shows aggregation-induced emissive (AIE) response in ≥70% aqueous media as well as in the solid state. The experimental results are well corroborated by time-resolved photoluminescence (TRPL) and density functional theory (DFT) calculations. An advanced-level OR-AND-NOT logic gate has been constructed from a different chemical combinational input and emission output. The reversible recognition of both Al³⁺ in MeOH-water (9:1, v/v) and Zn²⁺ in DMSO-water (9:1, v/v) is also ascertained in the presence of Na₂EDTA, enabling the construction of a molecular memory device. The probe H₂L also detects intracellular Al³⁺/Zn²⁺ ions in Hela cells. Altogether, our fundamental findings will pave the way for designing and synthesis of unique chemosensors that could be used for cell imaging studies as well as constructing molecular logic gates.

Utilizing Ag-Au core-satellite structures for colorimetric and surface-enhanced Raman scattering dual-sensing of Cu (II)

This study develops a dual-channel colorimetric and surface-enhanced Raman scattering (SERS) strategy for detection of Cu²⁺ utilizing Ag-Au core-satellite nanostructures. 4-mercaptobenzoic acid (MBA) modified Ag nanoparticles (AgNPs@MBA) and 4-mercaptopyridine (Mpy) capped AuNPs (GNPs@Mpy) are first designed via metal-sulfur bonds, respectively. Benefiting from the Cu²⁺-triggered NPs self-aggregation, the dispersion of AgNPs-GNPs (AgNPs@MBA + GNPs@Mpy) is turned into AgNPs-Cu²⁺-GNPs core-satellite structures. Because of the presence of pyridyl nitrogen and carboxy group which have specific coordination ability towards Cu²⁺, induces a certain aggregation of NPs. As well it can be obviously discerned by the visual assay and easily captured by SERS analysis. The UV-Vis method exhibits good linearity in the ranging from 0.1 μM-200 μM for Cu²⁺, while SERS method displays good linear response from 1 pM to 100 μM. The detection limit of Cu²⁺ is 0.032 μM by colorimetry and 0.6 pM by SERS method, which is significantly lower than the acceptable limit of Cu²⁺ in drinking water (20 μM) set by the US EPA. Furthermore, colorimetric and SERS assay based on AgNPs-Cu²⁺-GNPs core-satellite structures is used to determine Cu²⁺ in various waters and soils, and the detection results are consistent with the traditional atomic analysis methods. This work offers a new method for detecting Cu²⁺ in environmental samples, and the plasmonic nanostructure provides new entry point for development of multiplexed sensing platform for in-field application.

A novel imidazole derived colorimetric and fluorometric chemosensor for bifunctional detection of copper (II) and sulphide ions in environmental water samples

Herein, a novel "ON-OFF" colorimetric and fluorometric chemosensor; 1N-allyl-2-(2, 5-dimethoxyphenyl)-4, 5-diphenyl-1H-imidazole (ADPPI), was constructed for sequential determination of Cu²⁺ and S^2- ions in aqueous media. The interaction between chemosensor ADPPI and different metal cations was investigated using UV-VIS and fluorimetric spectroscopy. ADPPI showed a favorable and good interaction with Cu²⁺ ions producing blue colored solution peaked at 610 nm with blue fluorescence at λ_em. = 447 nm. The produced complex between Cu²⁺ ions and ADPPI can be used as a cascade probe for detection of S^2- ions. The detection limits (LODs) were 1.01 nM and 1.25 μM for Cu²⁺ and S^2- ions, respectively (the lowest between the family of colorimetric and fluorometric chemosensors). To further increase the applicability of the proposed method, Cu²⁺ and S^2- ions concentrations were measured in environmental water samples.

A selective purine-based fluorescent chemosensor for the “naked-eye” detection of zinc ions (Zn2+): applications in live cell imaging and test strips

In this work, a novel purine based probe PTAHN was successfully designed and synthesized. PTAHN displayed high selectivity towards Zn²⁺via turn-on fluorescence. What's more, PTAHN can be proficiently employed for imaging Zn²⁺ in living cells.

Coumarin based yellow emissive AIEE active probe: A colorimetric sensor for Cu2+ and fluorescent sensor for picric acid

A hydrazine derived ESIPT active Schiff base, 1-(8-methanylylidene-7-hydroxy-4-methyl-2H-chromen-2-one)-2-(2, 4-dihydroxybenzylidene) hydrazine, L was synthesized and characterized by elemental analysis and by various spectroscopic techniques. L exhibited a colourimetric response towards Cu²⁺ ion by changing from colorless to yellow with relatively a little or no interference of other common metal ions. The probe also showed good response for the detection of Cu²⁺ in real water samples. The H-aggregated L displayed AIEE property in acetonitrile/water mixture. The restriction of molecular motions endued the luminogen with a yellow fluorescence through ESIPT emission at 562 nm having relatively large Stock's shift of 205 nm. The scanning electron microscopic study was carried out to investigate the morphology of the nanoaggregate. The aggregated luminogen displayed it yellow emission in the pH range of 4-7 without affecting the intensity. The applicability of the probe for the detection of picric acid was also checked.

A novel fluorescent-colorimetric probe for Al3+ and Zn2+ ion detection with different response and applications in F- detection and cell imaging

A novel Schiff base fluorescence probe (HL) was synthesized by the condensation of salicylaldehyde and an 8-aminoquinoline derivative. This probe acts as a "turn-on" dual selectivity fluorescence probe for Zn²⁺ and Al³⁺ ions, providing different colors and detection limits (DL) of 11.5 and 23.5 nM, respectively. Moreover, when Zn²⁺ and Al³⁺ co-exist, HL exhibits a preference for Al³⁺ by displacing Zn²⁺ from the HL-Zn²⁺ complex, realizing a dual-channel signal output for Al³⁺. The HL-Al³⁺ system could further discern F^- by a "turn-off" fluorescence response with a DL of 86.0 nM. Furthermore, the probe HL was capable of monitoring intracellular Al³⁺, Zn²⁺ and F^- in living PC12 cells in vitro through fluorescence imaging, which proved its value in potential in vivo applications.

Crystal structure and DFT study of 8-hy-droxy-1,2,3,5,6,7-hexa-hydro-pyrido[3,2,1-ij]quinoline-9-carbaldehyde

In the title compound, C13H15NO2, the fused non-aromatic rings of the julolidine moiety adopt envelope conformations. The hy-droxy group forms an intra-molecular hydrogen bond to the aldehyde O atom, generating an S(6) ring motif. Weak inter-molecular C-H⋯O hydrogen bonds help to stabilize the crystal structure. Density functional theory (DFT) optimized structures at the B3LYP/6-311 G(d,p) level are compared with the experimentally determined mol-ecular structure in the solid state.

A highly selective chromogenic sensor for Mn2+, turn-off fluorometric for Hg2+ ion, and turn-on fluorogenic sensor for F- ion with the practical application

A colorimetric and fluorometric probe (E)-2-((8-hydroxy-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-9-yl)methylene)hydrazinecarbothioamide based on thiosemicarbazide and julolidine moieties has been synthesised in pure crystalline form and characterized by ¹H NMR, UV-vis, elemental analysis and single crystal XRD. The probe functioned as multitarget ion sensor, detect biologically important metal ions Hg²⁺ and Mn²⁺ in dual channel mode. Meanwhile, in mixed solvent media DMF/H₂O [8:2], probe displayed selectivity for Hg²⁺ over other cations by the emission spectrum. Interestingly probe has been explored to recognize F^- anion in DMF through ESIPT mechanism. The 1:1 binding stoichiometry of probe with Hg²⁺ and Mn²⁺ is confirmed by Job's plot through emission titration and UV-vis titration respectively. Probe is selective and sensitive to Hg²⁺ and Mn²⁺ with detection limit as low as 15μM and 0.2μM respectively. The sensing mechanism for selective ions was also scrutinized using ¹H NMR experiments and computational studies.

Crystal structure of (E)-9-({[4-(di-ethyl-amino)-phen-yl]imino}-meth-yl)-2,3,6,7-tetra-hydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol

The title compound, C23H29N3O, was synthesized from the condensation reaction of 8-hy-droxy-julolidine-9-carbaldehyde and N,N-diethyl-p-phenyl-enedi-amine. The hy-droxy group forms a intra-molecular hydrogen bond to the imine N atom and generates an S(6) ring motif. The conformation about the C=N bond is E, and the aromatic ring of the julolidine moiety is inclined to the benzene ring by 3.74 (14)°. One of the fused non-aromatic rings of the julolidine moiety adopts an envelope conformation and the other has a screw-boat conformation. In the crystal, mol-ecules are linked by C-H⋯π inter-actions involving the aromatic julolidine ring, forming slabs parallel to the bc plane. The tricyclic fragment of the julolidine ring and the azomethine C=N bond are disordered over two sets of sites with a refined occupancy ratio of 0.773 (3):0.227 (3).

Crystal structure of 9,9'-{(1E,1'E)-[1,4-phenyl-enebis(aza-nylyl-idene)]bis-(methanylyl-idene)}bis-(2,3,6,7-tetra-hydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol)

The whole mol­ecule of the title compound is generated by inversion symmetry; the central benzene ring being situated about a crystallographic inversion center. The aromatic ring of the julolidine moiety is inclined to the central benzene ring by 33.70 (12)°, and the conformation about the C=N bonds is E. There are two intra­molecular O—H⋯N hydrogen bonds in the mol­ecule, generating S(6) ring motifs.

The whole mol­ecule of the title compound, C₃₂H₃₄N₂O₂, is generated by inversion symmetry; the central benzene ring being situated about the crystallographic inversion center. The aromatic ring of the julolidine moiety is inclined to the central benzene ring by 33.70 (12)°. There are two intra­molecular O—H⋯N hydrogen bonds in the mol­ecule, generating S(6) ring motifs. The conformation about the C=N bonds is E. The fused non-aromatic rings of the julolidine moiety adopt half-chair conformations. In the crystal, adjacent mol­ecules are linked by pairs of C—H⋯π inter­actions, forming a ladder-like structure propagating along the a-axis direction.

Simultaneous bioimaging recognition of Al3+ and Cu2+ in living-cell, and further detection of F- and S2- by a simple fluorogenic benzimidazole-based chemosensor

A simple Schiff base (BMSA) prepared from salicylaldehyde and 2-(1H-benzo[d]imidazol-2-yl)aniline was evaluated as an efficient fluorescent chemosensor for the selective recognition of Al³⁺and Cu²⁺ over other common metal ions. This sensor could detect Al3⁺ in CH₃OH/PBS with distinct emission red-shift (the detection limit 0.31μM)and Cu²⁺in CH₃OH/Tris-HCL (the detection limit 0.54μM) with obvious fluorescence quenching. The obtained BMSA-Al³⁺ and BMSA-Cu²⁺ complexes could act as cascade sensors for detecting F^- and S^2-, respectively. The recognizing behavior of BMSA toward Al³⁺and Cu²⁺ has been investigated in detail through Job's Plot, FT-IR NMR, and HRMS analysis. Moreover, this chemosensor was verified to be of low cytotoxicity and good imaging characteristics for the detection of Al³⁺ and Cu²⁺, and further for the recognition of F^- and S^2- in living cells, suggesting that BMSA was proved to be a useful tool for tracking Al3⁺/Cu²⁺and F^-/S^2- ions in vivo.

Dioxo-vanadium(v), oxo-rhenium(v) and dioxo-uranium(vi) complexes with a tridentate Schiff base ligand

The complexation of a tridentate Schiff base ligand with three oxo-metal ions lead to the formations of four new complexes.

Colorimetric and ON–OFF–ON fluorescent chemosensor for the sequential detection of Cu(ii) and cysteine and its application in imaging of living cells

An easy-to-prepare colorimetric and ON–OFF–ON fluorescent naphthol derivative 1 has been used for sequential detection of Cu²⁺ and cysteine.

3d transition metal complexes with a julolidine–quinoline based ligand: structures, spectroscopy and optical properties

Five new complexes of a julolidine–quinoline based ligand with 3d transition metals have been synthesised and structurally characterised.

Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species

In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu²⁺, Fe²⁺/Fe³⁺, Zn²⁺and Hg²⁺.

A diaminomaleonitrile based selective colorimetric chemosensor for copper(ii) and fluoride ions

A chemosensor showed colorimetric sensing for copper(ii) and fluoride by changing color from yellow to colorless and to orange.