Anion recognition and sensing by transition-metal complexes with polarized N H recognition motifs

Insights into the anticancer photodynamic activity of Ir(III) and Ru(II) polypyridyl complexes bearing β-carboline ligands

Ir(III) and Ru(II) polypyridyl complexes are promising photosensitizers (PSs) for photodynamic therapy (PDT) due to their outstanding photophysical properties. Herein, one series of cyclometallated Ir(III) complexes and two series of Ru(II) polypyridyl derivatives bearing three different thiazolyl-β-carboline N^N' ligands have been synthesized, aiming to evaluate the impact of the different metal fragments ([Ir(C^N)2]+ or [Ru(N^N)2]2+) and N^N' ligands on the photophysical and biological properties. All the compounds exhibit remarkable photostability under blue-light irradiation and are emissive (605 < λem < 720 nm), with the Ru(II) derivatives displaying higher photoluminescence quantum yields and longer excited state lifetimes. The Ir PSs display pKa values between 5.9 and 7.9, whereas their Ru counterparts are less acidic (pKa > 9.3). The presence of the deprotonated form in the Ir-PSs favours the generation of reactive oxygen species (ROS) since, according to theoretical calculations, it features a low-lying ligand-centered triplet excited state (T1 = 3LC) with a long lifetime. All compounds have demonstrated anticancer activity. Ir(III) complexes 1-3 exhibit the highest cytotoxicity in dark conditions, comparable to cisplatin. Their activity is notably enhanced by blue-light irradiation, resulting in nanomolar IC50 values and phototoxicity indexes (PIs) between 70 and 201 in different cancer cell lines. The Ir(III) PSs are also activated by green (with PI between 16 and 19.2) and red light in the case of complex 3 (PI = 8.5). Their antitumor efficacy is confirmed by clonogenic assays and using spheroid models. The Ir(III) complexes rapidly enter cells, accumulating in mitochondria and lysosomes. Upon photoactivation, they generate ROS, leading to mitochondrial dysfunction and lysosomal damage and ultimately cell apoptosis. Additionally, they inhibit cancer cell migration, a crucial step in metastasis. In contrast, Ru(II) complex 6 exhibits moderate mitochondrial activity. Overall, Ir(III) complexes 1-3 show potential for selective light-controlled cancer treatment, providing an alternative mechanism to chemotherapy and the ability to inhibit lethal cancer cell dissemination.

Organoplatinum Complex Exhibiting Aggregation-Enhanced Emission (AEE) and Dual-Channel Ion-Sensing Properties by Terminating the Molecular Configuration Transformation (MCT) and Excited-State Intramolecular Proton Transfer (ESIPT)

Emitters produce weak emissions when they undergo structural changes such as molecular configuration transformation (MCT) or excited-state intramolecular proton transfer (ESIPT) but give out strong emissions after terminating these distortions. Herein, an organoplatinum complex, Pt-ppy-ABP, carrying a salicylaldehyde-based Schiff base unit is synthesized. It exhibits weak emission in dilute solutions but shows bright emission at the aggregated state or after interacting with F- and Zn2+. This suggests that it has an aggregation-enhanced emission (AEE) property and holds potential in ion detection. Supported by theoretical calculations and femtosecond transient absorption results, this complex suffers excited-state structural changes including MCT from a square-planar configuration to a tetrahedral one, as well as intramolecular rotation of a monodentate ligand and ESIPT, showing weak emission in its solutions. At the aggregated state, it releases strong yellow emissions because of the restraints of MCT and ligand rotation. Upon interacting with F- or Zn2+, it emits bright-red or -green emissions, achieving detection limits of 10-7 M. The sensing mechanism is concluded as deprotonation- and coordination-induced ESIPT terminations, respectively. Given its AEE property and ion-responsive emissions, its application in information encryption is also explored. Finally, these findings should provide valuable clues for the developments of chemosensors with dual-channel recognition abilities.

Fluorescent and chromogenic organic probes to detect group 10 metal ions: design strategies and sensing applications

Group 10 metals including Ni, Pd and Pt have been extensively applied in various essential aspects of human social life, material science, industrial manufactures, medicines and biology. The ionic forms of these metals are involved in several biologically important processes due to their strong binding capability towards different biomolecules. However, the mishandling or overuse of such metals has been linked to serious contamination of our ecological system, more specifically in soil and water bodies with acute consequences. Therefore, the detection of group 10 metal ions in biological as well as environmental samples is of huge significance from the human health point of view. Related to this, considerable efforts are underway to develop adequately efficient and facile methods to achieve their selective detection. Optical sensing of metal ions has gained increasing attention of researchers, particularly in the environmental and biological settings. Innovatively designed optical probes (fluorescent or colorimetric) are usually comprised of three basic components: an explicitly tailored receptor unit, a signalling unit and a clearly defined reporter unit. This review deals with the recent progress in the design and fabrication of fluorescent or colorimetric organic sensors for the detection of group 10 metal ions (Ni(II), Pd(II) and Pt(II)), with attention to the general aspects for design of such sensors.

A neutral rhenium-biimidazole complex for the selective recognition of fluoride ions

The neutral rhenium(I)-biimidazole complex [Re(CO)₃(biimH)(1,4-NVP)] (1) was designed and synthesized by a one-pot reaction of Re₂(CO)₁₀, 2,2'-biimidazole (biimH₂) and 4-(1-naphthylvinyl)pyridine (1,4-NVP). The structure of 1 was characterized by various spectroscopic techniques including IR, ¹H NMR, FAB-MS, and elemental analysis and further confirmed by a single-crystal X-ray diffraction analysis. The mononuclear complex 1, a relatively simple structure with an octahedral geometry, is comprised of facial-arranged carbonyl groups, one chelated biimH monoanion, and one 1,4-NVP. Complex 1 shows the lowest energy absorption band at around 357 nm and an emission band at 408 nm in THF. The luminescent characteristics of 1 combined with the hydrogen bonding ability of the partially coordinated monoionic biimidazole ligand permits the complex to selectively recognize fluoride ions (F^-) in the presence of other halides through a dramatic luminescence enhancement. The recognition mechanism of 1 can be convincingly explained in terms of H-bond formation and proton abstraction upon the addition of F^- ions by ¹H and ¹⁹F NMR titration experiments. The electronic properties of 1 were further supported by time dependent density functional theory (TDDFT) computational studies.

Development and Application of Ruthenium(II) and Iridium(III) Based Complexes for Anion Sensing

Improvements in the design of receptors for the detection and quantification of anions are desirable and ongoing in the field of anion chemistry, and remarkable progress has been made in this direction. In this regard, the development of luminescent chemosensors for sensing anions is an imperative and demanding sub-area in supramolecular chemistry. This decade, in particular, witnessed advancements in chemosensors based on ruthenium and iridium complexes for anion sensing by virtue of their modular synthesis and rich chemical and photophysical properties, such as visible excitation wavelength, high quantum efficiency, high luminescence intensity, long lifetimes of phosphorescence, and large Stokes shifts, etc. Thus, this review aims to summarize the recent advances in the development of ruthenium(II) and iridium(III)-based complexes for their application as luminescent chemosensors for anion sensing. In addition, the focus was devoted to designing aspects of polypyridyl complexes of these two transition metals with different recognition motifs, which upon interacting with different inorganic anions, produces desirable quantifiable outputs.

Indazole-Derived Mono-/Diruthenium and Heterotrinuclear Complexes: Switchable Binding Mode, Electronic Form, and Anion Sensing Events

The article deals with the newer classes of mononuclear: [(acac)₂Ru^III(H-Iz)(Iz^-)] 1, [(acac)₂Ru^III(H-Iz)₂]ClO₄ [1]ClO₄/[1']ClO₄, and [(bpy)₂Ru^II(H-Iz)(Iz^-)]ClO₄ [2]ClO₄, mixed-valent unsymmetric dinuclear: [(acac)₂Ru^III(μ-Iz^-)₂Ru^II(bpy)₂]ClO₄ [3]ClO₄, and heterotrinuclear: [(acac)₂Ru^III(μ-Iz^-)₂M^II(μ-Iz^-)₂Ru^III(acac)₂] (M = Co:4a, Ni:4b, Cu:4c, and Zn:4d) complexes (H-Iz = indazole, Iz^- = indazolate, acac = acetylacetonate, and bpy = 2,2'-bipyridine). Structural characterization of all the aforestated complexes established their molecular identities including varying binding modes (N_a and N_b donors and 1H-indazole versus 2H-indazole) of the heterocyclic H-Iz/Iz^- in the complexes. Unlike [1']ClO₄ containing two NH protons at the backface of H-Iz units, the corresponding [1]ClO₄ was found to be unstable due to the deprotonation of its positively charged quaternary nitrogen center, and this resulted in the eventual formation of the parent complex 1. A combination of experimental and density functional theory calculations indicated the redox noninnocent feature of Iz^- in the complexes along the redox chain. The absence of intervalence charge transfer transition in the near-infrared region of the (Iz^-)₂-bridged unsymmetric mixed-valent Ru^IIIRu^II state in [3]ClO₄ suggested negligible intramolecular electronic coupling corresponding to a class I setup (Robin and Day classification). Heterotrinuclear complexes (4a-4d) exhibited varying spin configurations due to spin-spin interactions between the terminal Ru(III) ions and the central M(II) ion. Though both [3]ClO₄ and 4a-4d displayed ligand (Iz^-/Iz^•)-based oxidation, reductions were preferentially taken place at the bpy and metal (Ru^III/Ru^II) centers, respectively. Unlike 1 or [2]ClO₄ containing one free NH proton at the backface of H-Iz, [1']ClO₄ with two H-Iz units could selectively and effectively recognize F^-, OAc^-, and CN^- among the tested anions: F^-, OAc^-, CN^-, Cl^-, Br^-, I^-, SCN^-, HSO₄^-, and Η₂PΟ₄^- in CH₃CN via intermolecular NH···anion hydrogen bonding interaction. The difference in the sensing feature between [1']ClO₄ and 1/[2]ClO₄ could be rationalized by their pK_a values of 8.4 and 11.3/10.8, respectively.

Cyclometalated Spirobifluorene Imidazolylidene Platinum(II) Complexes with Predominant 3LC Emissive Character and High Photoluminescence Quantum Yields

Two novel bidentate C^C*_spiro cyclometalated platinum(II) complexes comprising a spiro-conjugated bifluorene ligand and different β-diketonate auxiliary ligands are synthesized and characterized. Their preparation employs a robust and elaborate synthetic protocol commencing with an N-heterocyclic carbene precursor. Structural characterization by means of NMR techniques and solid-state structures validate the proposed and herein presented molecular scaffolds. Photophysical studies, including laser flash photolysis methods, reveal an almost exclusively ligand-centered triplet state, governed by the C^C*_spiro-NHC ligand. The high triplet energies and the long triplet lifetimes in the order of 30 μs in solution make the complexes good candidates for light-emitting diode-driven photocatalysis, as initial energy transfer experiments reveal. In-depth time-dependent density functional theory investigations are in excellent accordance with our spectroscopic findings. The title compounds are highly emissive in the bluish-green color region with quantum yields of up to 87% in solid-state measurements.

Anion and Temperature Responsive Molecular Switches Based on Trimetallic Complexes of Ru(II) and Os(II) That Demonstrate Advanced Boolean and Fuzzy Logic Functions

Anion- and temperature-induced alteration of the photoredox behaviors of our recently reported trimetallic complexes was carried out to fabricate potential molecular switches. The triads [(phen)₂Ru(d-HIm-t)M(t-HIm-d)Ru(phen)₂]⁶⁺ (phen = 1,10-phenanthroline, d-HIm-t = heterotopic bipyridine-terpyridne type bridging ligand, and M = Ru^II and Os^II) possess two acidic imidazole NH protons that upon interaction with anions give rise to considerable changes in their photophysical and electrochemical behaviors. Red-shifts of the absorption and emission maximum and a decrease in the M³⁺/M²⁺ potential occur when the triads are treated with basic anions. In fact, the triads can function as triple-channel sensors for F^-, AcO^-, CN^-, OH^-, and H₂PO₄^- in acetonitrile and as selective probes for CN^- and SCN^- in water. The equilibrium constants for the receptor-anion interaction are on the order of 10⁶ M^-1, while the limit of detection was on the order of 10^-9 M. Temperature plays a key role in the luminescence properties of the triads by adjusting the energy barrier between the emitting triplet metal-to-ligand charge transfer and non-emitting triplet metal-centered levels. A decrease in temperature leads to increases in the emission intensity and lifetime of the triads displaying the "on state", whereas an increase in temperature leads to a decrease in their emission characteristics and thus indicates the "off state" and that the process is fully reversible. In essence, the triads could function as potential switches on the basis of the reversible change in their spectral and redox behaviors under the influence of anion, acid, and temperature. The most important outcome of this study is mimicking several advanced Boolean and fuzzy logic functions by utilizing the spectral response of the triads upon the action of said external stimuli.

A fundamental role of solvent polarity and remote substitution of 2-(4-R-phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline framework in controlling of ground- and excited-state properties of Re(I) chromophores [ReCl(CO)3(R-C6H4-imphen)]

A series of Re(I) carbonyl chromophores with 1H-imidazo[4,5-f][1,10]phenanthroline (imphen) ligand functionalized with electron-donating amine groups attached to the imidazole ring via phenylene linkage was designed to investigate the impact of...

The C2-Symmetry Colorimetric Dye Based on a Thiosemicarbazone Derivative and its Cadmium Complex for Detecting Heavy Metal Cations (Ni2+, Co2+, Cd2+, and Cu2+) Collectively, in DMF

The field of chemosensing has been experiencing an exponential expansion in recent times, due to increased demands for simpler and user-friendly analytical techniques, in order to combat and confront the challenges of industrial pollutions in the twenty-first century. Metal complex-based chemosensors have received little attention while exhibiting excellent sensing properties, comparing to their organic counterparts. Thus, a thiosemicarbazone-based (H) and its cadmium complex (P) were synthesized, characterized and their photophysical and chemosensing properties were investigated in DMF solvent. The addition of molar equivalents of selected cations (of nitrates or chloride salts) to H and P, produced visually detectable colour changes as well as remarkable spectral shifts. Explicitly, the two probes (H and P) were able to collectively discriminate heavy metal cations such as Cd2+, Co2+, Zn2+, Cu2+, Ni2+, and Ag+, both in DMF, among all other heavy metal cations tested. None of the anions could be detected by H or P, even when the tetrabutylammonium salts (TBAs) were used, the action presumably ascribed to the solvent effect. Thus, H and P can be used to selectively and sensitively detect the presence of heavy metal cations, via naked-eye detectable colour changes in an aqueous soluble solvent such as DMF.

Exploitation of the Second Coordination Sphere to Promote Significant Increase of Room-Temperature Luminescence Lifetime and Anion Sensing in Ruthenium-Terpyridine Complexes

This paper deals with the synthesis, characterization, and photophysical behaviors of three Ru(II)-terpyridine complexes derived from a terpyridyl-imidazole ligand (tpy-HImzPh₃Me₂), wherein a terpyridine moiety has been coupled with a dimethylbenzil unit through a phenylimidazole spacer. The three complexes display strong emission at RT having excited-state lifetimes in the range of 2.3-43.7 ns, depending upon the co-ligand present and the solvents used. Temperature-dependent emission spectral measurements have demonstrated that the energy separation between emitting metal-to-ligand charge transfer state and non-emitting metal-centered state is increased relative to that of [Ru(tpy)₂]²⁺. In contrast to our previously studied Ru(II) complexes containing similar terpyridyl-imidazole motif but differing by peripheral methyl groups, significant enhancement of RT emission intensity and quantum yield and remarkable increase of emission lifetime occur for the present complexes upon protonation of the imidazole nitrogen(s) with perchloric acid. Additionally, by exploiting imidazole NH motif(s), we have examined their anion recognition behaviors in organic and aqueous media. Interestingly, the complexes are capable of visually recognizing cyanide ions in aqueous medium up to the concentration limit of 10^-8 M. Computational studies involving density functional theory (DFT) and time-dependent DFT methods have been carried out to obtain insights into their electronic structures and to help with the assignment of absorption and emission bands.

A Metal-Based Receptor for Selective Coordination and Fluorescent Sensing of Chloride

A scorpionate Zn²⁺ complex, constituted by a macrocyclic pyridinophane core attached to a pendant arm containing a fluorescent pyridyl-oxadiazole-phenyl unit (PyPD), has been shown to selectively recognize chloride anions, giving rise to changes in fluorescence emission that are clearly visible under a 365 nm UV lamp. This recognition event has been studied by means of absorption, fluorescence, and NMR spectroscopy, and it involves the intramolecular displacement of the PyPD unit by chloride anions. Moreover, since the chromophore is not removed from the system after the recognition event, the fluorescence can readily be restored by elimination of the bound chloride anion.

Anion-Recognition Studies of a Rhenium(I) 4-Mercaptopyridine Compound and Its Ligand-Coupling Products

The reaction of Re(CO)₅Cl with 4-mercaptopyridine (4-PySH) led to the formation of [Re(CO)₃(4-HPyS)₃]Cl (1), showing three hydrogen-bonding donors of 4-PySH ligands as well as a characteristic ligand-to-metal charge-transfer absorption at ca. 380 nm. In this regard, a variety of anions, i.e., CN^-, OAc^-, F^-, Cl^-, Br^-, I^-, PF₆^-, NO₃^-, ClO₄^-, and H₂PO₄^-, were examined to study anion-recognition studies through hydrogen-bonding functionalities. Upon the addition of CN^- to a methanolic solution of complex 1, a remarkable spectral change with an isosbestic point at ca. 314 nm in the absorption spectra was observed, with a binding constant (K_b) calculated to be 24770 M^-1. Moreover, the OAc^- anion also shows a similar trend, but a mild spectral change, with K_b calculated to be 2170 M^-1. Unlike those of CN^- and OAc^-, the addition of F^-, Cl^-, Br^-, and I^- anions causes a less pronounced spectral change with an isosbestic point at ca. 350 nm and K_b calculated to be 2863-750 M^-1. However, almost no spectral change can be observed for other anions (i.e., PF₆^-, NO₃^-, H₂PO₄^-, and ClO₄^-). Interestingly, the molecular loops of [Re(CO)₃Cl(Py₂S₂)]₂ (2; Py₂S₂ = 4,4'-dipyridyl disulfide) and [Re(CO)₃Cl(Py₂S)_0.35(Py₂S₂)_0.65]₂ (3; Py₂S = 4,4'-dipyridyl sulfide) can be isolated and structurally characterized by X-ray diffraction, where those crystals were grown from diethyl ether diffusion into a methanolic solution of complex 1 with [Bu₄N]CN and [Bu₄N]NO₃, respectively. It is noted that such unusual ligand-coupling reactions toward the homoligand and hybrid-ligand loops of complexes 2 and 3 can be achieved at room temperature in this study.

Facile and Reliable Emission-Based Nanomolar Anion Sensing by Luminescent Iridium Receptors Featuring Chelating Halogen-Bonding Sites

An anion sensor is presented that combines a bidentate hydrogen‐ (HB) or halogen‐bonding (XB) site with a luminescent monocationic Ir fragment for strong binding of common anions (K_a up to 6×10⁴  m⁻¹) with diagnostic emission changes. A new emission‐based protocol for fast and reliable detection was derived on the basis of correction for systematic but unspecific background effects. Such a simple correction routine circumvents the hitherto practical limitations of systematic emission‐based analysis of anion binding with validated open‐source software (BindFit). The anticipated order of K_a values was obeyed according to size and basicity of the anions (Cl>Br=OAc) as well as the donor atom of the receptor (XB: 6×10⁴  m⁻¹ > HB: 5×10³  m⁻¹), and led to submicromolar limits of detection within minutes. The results were further validated by advanced NMR techniques, and corroborated by X‐ray crystallographic data and DFT analysis, which reproduced the structural and electronic features in excellent agreement. The results suggest that corrected emission‐based sensing may become a complementary, reliable, and fast tool to promote the use of XB in various application fields, due to the simple and fast optical determination at high dilution.

Near-infrared absorbing Ru(ii) complexes act as immunoprotective photodynamic therapy (PDT) agents against aggressive melanoma

Mounting evidence over the past 20 years suggests that photodynamic therapy (PDT), an anticancer modality known mostly as a local treatment, has the capacity to invoke a systemic antitumor immune response, leading to protection against tumor recurrence. For aggressive cancers such as melanoma, where chemotherapy and radiotherapy are ineffective, immunomodulating PDT as an adjuvant to surgery is of interest. Towards the development of specialized photosensitizers (PSs) for treating pigmented melanomas, nine new near-infrared (NIR) absorbing PSs based on a Ru(ii) tris-heteroleptic scaffold [Ru(NNN)(NN)(L)]Cl_n, were explored. Compounds 2, 6, and 9 exhibited high potency toward melanoma cells, with visible EC₅₀ values as low as 0.292–0.602 μM and PIs as high as 156–360. Single-micromolar phototoxicity was obtained with NIR-light (733 nm) with PIs up to 71. The common feature of these lead NIR PSs was an accessible low-energy triplet intraligand (³IL) excited state for high singlet oxygen (¹O₂) quantum yields (69–93%), which was only possible when the photosensitizing ³IL states were lower in energy than the lowest triplet metal-to-ligand charge transfer (³MLCT) excited states that typically govern Ru(ii) polypyridyl photophysics. PDT treatment with 2 elicited a pro-inflammatory response alongside immunogenic cell death in mouse B16F10 melanoma cells and proved safe for in vivo administration (maximum tolerated dose = 50 mg kg⁻¹). Female and male mice vaccinated with B16F10 cells that were PDT-treated with 2 and challenged with live B16F10 cells exhibited 80 and 55% protection from tumor growth, respectively, leading to significantly improved survival and excellent hazard ratios of ≤0.2.

Ru(ii) photosensitizers (PSs) destroy aggressive melanoma cells, triggering an immune response that leads to protection against tumor challenge and mouse survival.

Anion sensing properties of electrospun nanofibers incorporating a thiourea-based chromoionophore in methanol

To sense hydrophilic anions in protic solvents, we fabricated polymethylmethacrylate (PMMA) nanofibers incorporating 4-nitrophenyl azo thiourea polymer as a chromoionophore. When methanol solutions containing anions contacted the PMMA nanofiber, a bathochromic shift from 386 nm was observed in the absorption maximum of the chromoionophore. This spectral change is due to hydrogen bond formation between the urea moiety of the thiourea-based polymer and anions penetrating the nanofiber. This spectral change was not observed in PMMA film incorporating the same anion sensor, and the difference is attributed to the much larger specific surface area of the nanofiber compared to the film. As a result, many anions could react with the anion-sensing polymers in the nanofiber and induce a large spectral response.

Zn2+ and Cu2+ complexes of a fluorescent scorpiand-type oxadiazole azamacrocyclic ligand: crystal structures, solution studies and optical properties

A ligand comprised of a macrocyclic pyridinophane core having a pendant arm containing a secondary amine group linked through a methylene spacer to a pyridyl-oxadiazole-phenyl (PyPD) fluorescent system has been prepared (L). The crystal structures of [ZnL](ClO₄)₂ and [CuL](ClO₄)₂ show that M²⁺ is coordinated to all the nitrogen atoms of the macrocyclic core, the secondary amine of the pendant arm and the nitrogen atom of the pyridine group of the fluorescent moiety, the latter bond being clearly weaker than the one with the pyridine of the macrocycle. Solution studies showed the formation of a highly stable Cu²⁺ complex with 1 : 1 stoichiometry, whereas with Zn²⁺ least stable complexes were formed and, given the right conditions, a [Zn₃L₂]⁶⁺ species was also detected, but it was not possible to isolate this species in the solid state. Following Zn²⁺ coordination, a strong chelation-induced enhancement of fluorescence was observed, a behaviour that was not observed with any of the other metal cations tested.

A new fluorescent hemicryptophane for acetylcholine recognition with an unusual recognition mode

The ammonium of the target interacts with the south part of the hemicryptophane probably because the cyclotriveratrylene's electronic density is altered by the extension of conjugation.

Naked-eye repeatable off–on–off and on–off–on switching luminescence of copper(i)-1H-imidazo[4,5-f][1,10]phenanthroline complexes with reversible acid–base responses

Repeatable off–on–off or on–off–on luminescence of a series of Cu(i) complexes is observed with reversible base–acid or acid–base responses.

1IL and 3MLCT excited states modulated by H+: the structure and photophysical properties of [(2-bromo-5-(1H-pyrazol-1-yl)pyrazine)Re(CO)3Br]

The photophysical characterization of pyrazolyl–pyrazine Re(i) complex, shows a ¹IL and ³MLCT excited states, being just the ³MLCT able to react with trifluoroacetic acid to yield the protonated and long-lived ³ILH⁺ species. These findings make the compound a potential sensor for protons in solution in the presence of light.

A recyclable hydroxyl functionalized polyindole hydrogel for sodium hydroxide extraction via the synergistic effect of cation–π interactions and hydrogen bonding

We have successfully constructed a new type of recyclable indole-based hydrogel, which exhibited highly effective extraction behavior for hydroxide via the synergistic effect of cation–π interactions and hydrogen bonds.

A fluorescent turn-on probe for cyanide anion detection based on an AIE active cobalt(ii) complex

A Co(ii) complex based on an AIE-active tetraarylethylene ligand displays selective fluorescence enhancement in the presence of cyanide anion in aqueous solution.

Synthesis, crystal structure, fluorescence properties of 1D chain Manganese (II) and Cadmium (II) complexes

Two complexes, {[Mn(3-pmpmd)₂(Cl)₂]·2H₂O}_n(1), {[Cd(3-pmpmd) (I)₂]·CHCl₃·H₂O}_n(2), (3-pmpmd, N,N'-bis(3-pyridylmethyl)pyromellitic diimide) were synthesized and characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses, and X-ray single-crystal structure analysis. The conformations of 3-pmpmd ligand affect their structural diversity. Complex 1 is a 1D double chain structure in edge-to-edge arrangement by π⋯π interactions. Complex 2 is a typical 1D zigzag chain structure arranged in a parallel array containing 1D channel to accommodate the chloroform and water guest molecules. Thermal stabilities and fluorescence properties of both complexes were investigated. The solution of complex 2 in DMF can sense for I^- anion by quenching fluorescence intensity, whereas other anions increasing fluorescence intensity.

Optical Sensing of Anions via Supramolecular Recognition with Biimidazole Complexes

Phosphorescent metal complexes with peripheral N-H donor functionalities have attracted great attention as potential molecular sensing units for anionic species lately. In this contribution we discuss the development and potential of anion recognition and sensing features of recent examples of luminescent 2,2'-biimidazole complexes of ruthenium(II), iridium(III), osmium(II) and cobalt(III). The general dependency of photophysical features in these complexes regarding the acid-base chemistry of the peripheral N-H functionalities will be outlined as a basic requirement for optical ion recognition. Systematic strategies for the tuning and specific improvement by synthetic means will be discussed regarding recent reports. With respect to their distinct photophysical features, different transition metals are considered individually to demonstrate particular trends regarding ligand modification within the respective groups. In summary, this review elucidates the current state-of-the-art and future potential of the versatile class of 2,2'-biimidazole based sensor chromophores.