Dual stimuli-responsive phosphorescence of a Pb(II) coordination polymer to acidic vapors and thermal treatment

We present a new intensely phosphorescent Pb(II) coordination polymer (1) containing a heteroatomic ligand. It has a quantum yield of 21.62% and a lifetime of 25.46 μs. The naked-eye solid-state photoluminescence of 1 significantly changes in response to acidic vapors and thermal treatment, indicating the coexistence of acidochromic and thermochromic luminescence.

Crystal structure of tetraaqua-bis[4-(1H-1,2,4-triazol-1-yl)benzoato-κ1 N]zinc(II), C18H20ZnN6O8

C18H20ZnN6O8, Triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 6.1830(5) Å, b = 7.0301(6) Å, c = 12.1369(11) Å, α = 80.665(1)°, β = 87.976(2)°, γ = 72.051(1)°, V = 495.17(7) Å3, Z = 1, Rgt (F) = 0.0495, wRref (F 2) = 0.1243, T = 298.15 K.

Coordination networks for the recognition of oxo-anions

Crystalline coordination networks with an infinite extended framework, also known as coordination polymers (CPs) or metal-organic frameworks (MOFs), have attracted significant attention owing to their tremendous performance in an extensive range of applications. The unique structural features and high stability of coordination networks are responsible for their utilization and potential in diverse fields especially in the area of sensing using luminescent CPs/MOFs. The recognition of toxic oxo-anions present in water is a crucial and first step towards environmental remediation, mainly in the case of water pollution. Accordingly, the utilization of luminescent coordination networks has received significant interest, particularly for the recognition of various toxic oxo-anions, which are considered a threat to aquatic life and the environment. In this frontier article, we summarize recent reports on luminescent CPs/MOFs, their utilization for the sensing of oxo-anions and the chemistry of the interaction of oxo-anions with CPs/MOFs, which is responsible for tuning their optical signals.

Metal-Organic Frameworks for Liquid Phase Applications

In the last two decades, metal-organic frameworks (MOFs) have attracted overwhelming attention. With readily tunable structures and functionalities, MOFs offer an unprecedentedly vast degree of design flexibility from enormous number of inorganic and organic building blocks or via postsynthetic modification to produce functional nanoporous materials. A large extent of experimental and computational studies of MOFs have been focused on gas phase applications, particularly the storage of low-carbon footprint energy carriers and the separation of CO2-containing gas mixtures. With progressive success in the synthesis of water- and solvent-resistant MOFs over the past several years, the increasingly active exploration of MOFs has been witnessed for widespread liquid phase applications such as liquid fuel purification, aromatics separation, water treatment, solvent recovery, chemical sensing, chiral separation, drug delivery, biomolecule encapsulation and separation. At this juncture, the recent experimental and computational studies are summarized herein for these multifaceted liquid phase applications to demonstrate the rapid advance in this burgeoning field. The challenges and opportunities moving from laboratory scale towards practical applications are discussed.

Eight Cd(ii) coordination polymers with persistent room-temperature phosphorescence: intriguing dual emission and time-resolved afterglow modulation

A new series of p-RTP CPs 1–8 were designed and successfully synthesized; 5–8, in particular, exhibited intriguing time-resolved afterglow modulation.

Luminescent metal–organic framework-based phosphor for the detection of toxic oxoanions in an aqueous medium

Compound 1 has been utilized for the luminescence based visible detection of chromate, permanganate and phosphate ions in aqueous medium.

From lamellar net to bilayered-lamella and to porous pillared-bilayer: reversible crystal-to-crystal transformation, CO2 adsorption, and fluorescence detection of Fe3+, Al3+, Cr3+, MnO4−, and Cr2O72− in water

Layered coordination polymers of different network topologies have showed reversible structural transformations and fluorescence detection toward Fe³⁺, Al³⁺, Cr³⁺, MnO₄^–, and Cr₂O₇^2– in water.

Luminescent coordination polymers constructed using a mixed-ligand strategy for highly selective luminescence sensing of nitrobenzene, Fe3+ and Cr2O72− ions and photodegradation of rhodamine B

Using a mixed ligand strategy, ten new LCPs were constructed. They all display highly sensitive and selective luminescence sensing for NB, Cr₂O₇²⁻and Fe³⁺ ions. Moreover, 3–10 also exhibit high photocatalytic activities toward the degradation of RhB.

Safranin O-functionalized cuboid mesoporous silica material for fluorescent sensing and adsorption of permanganate

A new safranin O-based chelating fluorophore coupled, dual-functionalized organic–inorganic hybrid material has been prepared for simultaneous MnO₄⁻ detection and adsorption in aqueous media and living organisms such as limnodrilus claparedianus and zebrafish.

A water-stable zinc(ii)-organic framework as a multiresponsive luminescent sensor for toxic heavy metal cations, oxyanions and organochlorine pesticides in aqueous solution

A novel metal-organic framework with the formula [Zn3(DDB)(DPE)]·H2O (1) (H5DDB = 3,5-di(2',4'-dicarboxylphenyl)benzoic acid and DPE = 1,2-di(4-pyridyl)ethylene) has been solvothermally synthesized by employing a rigid carboxylate ligand H5DDB to assemble with Zn(ii) ions in the presence of a flexible bis(pyridyl) linker DPE. The Zn-MOF is a 3D framework with six-nuclear clusters and possesses remarkable water stability and pH stability. Interestingly, complex 1 can sensitively and selectively sense Fe(iii), Cr(iii), Cr(vi), Mn(vii) and the pesticide 2,6-Dich-4-NA with low detection limits in aqueous solution. Moreover, complex 1 also exhibits selectivity for 2,6-Dich-4-NA detection in real samples including carrot, grape and nectarine extracts, and its detection ability is almost unchanged in the presence of the surfactant sodium dodecyl sulfate (SDS). The possible mechanisms of luminescence quenching have been explained by the weak affinity of nitrogen atoms, resonance energy transfer, and photoinduced electron transfer. To our knowledge, this is the first example of a MOF-based multiresponsive fluorescent probe for the simultaneous detection of Fe(iii), Cr(iii/vi), Mn(vii) and the pesticide 2,6-Dich-4-NA in aqueous solution.

Devising Chemically Robust and Cationic Ni(II)-MOF with Nitrogen-Rich Micropores for Moisture-Tolerant CO2 Capture: Highly Regenerative and Ultrafast Colorimetric Sensor for TNP and Multiple Oxo-Anions in Water with Theoretical Revelation

Metal-organic frameworks (MOFs) show distinctive superiority for carbon dioxide (CO₂) capture and luminescent sensing of toxic pollutants over other materials, where combination of both of these properties together with improvement of hydrolytic stability and pore functionality is critical to environmental remediation applications. The Ni(II) framework [Ni₂(μ₂-OH)(azdc)(tpim)](NO₃)·6DMA·6MeOH (CSMCRI-3) (tpim = 4,4',4″-(1H-imidazole-2,4,5-triyl)tripyridine, H₂azdc = azobenzene-4,4'-dicarboxylic acid, DMA = dimethylacetamide, CSMCRI = Central Salt & Marine Chemicals Research Institute), encompassing cationic [Ni₂(μ₂-OH)(CO₂)₂] SBUs, is solvothermally synthesized from nitrogen-rich and highly fluorescent organic struts. The noninterpenetrated structure, containing free nitrogen atom affixed microporous channels, is stable in diverse organic solvents and weakly basic and acidic aqueous solutions. The activated MOF (3a) exhibits strong CO₂-framework interaction and extremely selective CO₂ adsorption over N₂ (292.5) and CH₄ (11.7). Importantly, water vapor exposure does not affect the surface area and/or multiple CO₂ uptake-release cycles, signifying potential of the porous structure for long-term use under humid conditions. Aqueous-phase sensing studies illustrate extremely specific and ultrafast detection of explosive 2,4,6-trinitrophenol (TNP) via remarkable fluorescence quenching (K_SV = 1.3 × 10⁵ M^-1), with a 0.25 ppm limit of detection (LOD). Furthermore, 3a serves as unique luminescent probe for highly discriminative and quick responsive detection of three noxious oxo-anions (Cr₂O₇^2-, CrO₄^2-, MnO₄^-) in water via noteworthy turn-off responses and extreme low LODs (Cr₂O₇^2- 0.9; CrO₄^2- 0.29; MnO₄^- 0.25 ppm). It is imperative to stress the outstanding reusability of the MOF toward multicyclic sensing of all four major water contaminants, alongside visible colorimetric changes upon individual analyte detection. Mechanistic insights in light of the electron transfer route together with density functional theory calculations portray the influence of pore functionalization in framework-analyte interactions, including alternation in energy levels, where varying degrees of contribution of energy transfer explicitly authenticates high quenching of the material.

Series of Water-Stable Lanthanide Metal-Organic Frameworks Based on Carboxylic Acid Imidazolium Chloride: Tunable Luminescent Emission and Sensing

A series of isomorphic lanthanide metal-organic frameworks (Ln-MOFs), {[Ln(L)(H₂O)₂]·5H₂O}_n (1-Ln, where Ln = Eu, Tb, Gd, and Eu_xTb_1-x), have been synthesized by a rigid 1,3-bis(3,5-dicarboxyphenyl)imidazolium chloride (H₄L⁺Cl^-) ligand and Ln³⁺ ions via a solvothermal method. Single-crystal X-ray diffraction indicated that 1-Ln exhibited similar three-dimensional porous frameworks with one-dimensional channels decorated by the uncoordinated carboxylate oxygen atoms. The luminescent sensing studies indicated that 1-Eu is an outstanding reusable luminescent probe suitable for the simultaneous detection of Cr₂O₇^2-, CrO₄^2-, and MnO₄^- ions in an aqueous solution. Remarkably, the different proportions of Eu³⁺ and Tb³⁺ can be combined into the same Ln-MOF to yield a new series of differently doped 1-Eu_xTb_1-x MOFs. At the same excitation wavelength, they generated dual-emission peaks of Eu³⁺ and Tb³⁺ to show a gradual change in luminous color between yellow-green, yellow, orange, orange-red, and red. On the basis of the excellent optical properties of 1-Ln complexes, they can be employed as promising luminescent probe and multicolor tunable photoluminescence materials.

A water-stable La-MOF with high fluorescence sensing and supercapacitive performances

A 3D lanthanide coordination polymer {[La(SIP)(H₂O)₃]·H₂O}_n (La-MOF) was synthesized successfully by the solvothermal reaction of La(NO₃)₃·6H₂O and 5-sulfoisophthalic acid monosodium salt (NaH₂SIP). In particular, two oxygen atoms of sulfate participate in the coordination, which is unusual in all the complexes. La-MOF was characterized by single-crystal X-ray diffraction, IR spectroscopy, powder X-ray diffraction, thermal-gravimetric analysis, and X-ray photoelectron spectroscopy. La-MOF shows excellent water stability and chemical stability in a broad pH range from 2 to 13. Moreover, the fluorescence and sensing properties of La-MOF were invsetigated in detail via its titration and cycling processes, revealing its highly efficient and selective quenching responses and good recyclability for the detection of Fe³⁺, Cr₂O₇^2- and CrO₄^2- ions. In addition, La-MOF possesses an outstanding specific capacitance of 213 F g^-1 at 0.5 A g^-1. It still retains 92% of the original capacitance after 2000 cycles, exhibiting remarkable long-term cycling stability and reversibility; therefore, the electrode material based on La-MOF is a competitive and promising candidate for application in supercapacitors.

Two exceptionally stable luminescent MOFs for the selective and sensitive detection of Fe3+ ions in aqueous solution

Two exceptionally stable MOFs were selected as highly efficient sensors for the rapid, sensitive and selective detection of Fe³⁺ in aqueous solution.

A fluorescent probe for sequential sensing of MnO4− and Cr2O72− ions in aqueous medium based on a UCNS/TMB nanosystem

Distinguishable and sequential detection of MnO₄⁻ and Cr₂O₇²⁻ was realized by the reactions above and IFE between UCNS and oxTMB.