Self-assembled discrete molecules for sensing nitroaromatics

Reversible reduction drives anion ejection and C60 binding within an FeII 4L6 cage

Fe^II₄L₆ tetrahedral cage 1 was prepared from a redox-active dicationic naphthalenediimide (NDI) ligand. The +20 charge of the cage makes it a good host for anionic guests, with no binding observed for neutral aromatic molecules. Following reduction by Cp₂Co, the cage released anionic guests; subsequent oxidation by AgNTf₂ led to re-uptake of anions. In its reduced form, however, 1 was observed to bind neutral C₆₀. The fullerene guest was subsequently ejected following cage re-oxidation. The guest release process was found to be facilitated by anion-mediated transport from organic to aqueous solution. Cage 1 thus employs electron transfer as a stimulus to control the uptake and release of both neutral and charged guests, through distinct pathways.

Fe^II₄L₆ cage 1 binds anionic guests but not neutral guests. In its reduced form, the cage can bind neutral C₆₀. Reduction and oxidation of the cage could thus be used as a stimulus to control the uptake and release of both neutral and charged guests.

Dy(III)-Based Metal-Organic Framework as a Fluorescent Probe for Highly Selective Detection of Picric Acid in Aqueous Medium

A dysprosium metal-organic framework, {[Dy(μ₂-FcDCA)_1.5(MeOH)(H₂O)]·0.5H₂O}_n (1), where FcDCA = 1,1'-ferrocene dicarboxylic acid, was prepared by slow-diffusion technique at room temperature. The crystal structure analysis of 1 by single-crystal X-ray diffraction reveals different binding modes of FcDCA linkers coordinated with Dy(III) metal ions, which forms continuous porous two-dimensional (2D) infinite framework. The resulting 2D layers are linked by π···π interactions to build three-dimensional (3D) supramolecular framework. Observably, this thermally stable 3D architecture was topologically simplified as a three-connected uninodal net with fes topology. Furthermore, the practical applicability of 1 was investigated as a fluorescence sensor for the sensitive detection of picric acid in aqueous medium with an impressive detection limit of 0.71 μM with quenching constant (K_SV) quantified to be 8.55 × 10⁴ M^-1. The distinguished selectivity in the presence of other nitroaromatics suggests the possible incorporation of 1 in real-world futuristic diagnostic kits. Additionally, the electrochemical behavior of 1 exhibits reversible in nature attributed to the ferrocene/ferrocenium cation.

Design of a Multifunctional Indium-Organic Framework: Fluorescent Sensing of Nitro Compounds, Physical Adsorption, and Photocatalytic Degradation of Organic Dyes

The detection of nitro compounds and removal of organic dyes remain urgent issues because they are poisonous to humans. Taking advantage of metal-organic framework (MOF) materials, we demonstrate herein an indium-organic framework (InOF) exhibiting sensitive fluorescence sensing of nitro compounds, prominent dye capture, and excellent photodegradation of dyes. By using 4,4',4″-s-triazine-1,3,5-triyltri-p-aminobenzoate (TATAB), an amino-functionalized BTB-like linker, the 3D SNNU-110 structure ({[In₃OCl(H₂O)₂(TATAB)₂]}_n) is formed. SNNU-110 shows a 3,6-connected 3,6T22 topology with TATAB and [In₃O(CO₂)₆] tricapped trigonal-prismatic clusters as 3- and 6-connected nodes. Thanks to the fluorescence properties and amine recognition sites of TATAB, SNNU-110 exhibits excellent performance of fluorescence quenching for six electron-deficient nitroaromatics. The intercrossing 1D channels in SNNU-110 formed from the a- and b-axis directions with dimensions of about 18 Å × 11 Å can capture diverse cationic, anionic, or neutral dyes effectively. What is more, the existence of an inorganic [In₃O] cluster enable SNNU-110 to be a good photocatalyst. Upon irradiation with a 300 W xenon lamp, SNNU-110 shows outstanding photocatalytic activity toward rhodamine B (RhB) and methylene blue (MB), and there was almost no degradation. The catalytic activity can retain about 94.6% (RhB) and 93.1% (MB), respectively. Overall, SNNU-110 fully demonstrates the power of multicomponent MOFs, which provide a feasible route for the design of functional materials toward to pollutant identification and removal applications.

Coordination-Driven Self-Assembly of Triazole-Based Apoptosis-Inducible Metallomacrocycles

Ru(II)-metallomacrocycles containing 4-pyridyl-1,2,3-triazole moiety were realized by coordination-driven self-assembly. All new compounds were characterized by electrospray ionisation mass spectrometry, elemental analysis, and 1H and 13C NMR spectroscopic techniques. The molecular structure of metallomacrocycle 8 was determined by single-crystal X-ray crystallography. The anticancer activities of metallomacrocycles 5-8 were evaluated by cytotoxicity, cell cycle analysis, and related protein expression. Metallomacrocycle 7 showed the highest cytotoxicity in HepG2 human hepatocellular carcinoma cells. In addition, apoptotic HepG2 cells were analyzed when metallomacrocycle 7 was treated. Our results suggest that metallomacrocycle 7 induces liver cancer cell death by increasing apoptosis and cell cycle arrest and that it has potential use as an agent for the treatment of human hepatocellular carcinoma.

Preparation, characterization and luminescence-sensing properties of two ZnII MOFs with mixed 5-amino-2,4,6-tribromoisophthalic acid and bipyridyl-type ligands

The bromo-substituted aromatic dicarboxylic acid 5-amino-2,4,6-tribromoisophthalic acid (H2ATBIP), in the presence of the N-donor flexible bipyridyl-type ligands 1,3-bis(pyridin-4-yl)propane (bpp) and N,N′-bis(pyridin-4-ylmethyl)oxalamide (4-bpme) and ZnII ions, was used as an O-donor ligand to assemble two novel luminescent metal–organic frameworks (MOFs), namely poly[[(μ-5-amino-2,4,6-tribromoisophthalato-κ2 O 1:O 3)[μ-1,3-bis(pyridin-4-yl)propane-κ2 N:N′]zinc(II)] dimethylformamide monosolvate], {[Zn(C8H2Br3NO4)(C13H14N2)]·C3H7NO} n , (1), and poly[[(μ-5-amino-2,4,6-tribromoisophthalato-κ2 O 1:O 3)diaqua[μ-N,N′-bis(pyridin-4-ylmethyl)oxalamide-κ2 N:N′]zinc(II)] monohydrate], {[Zn(C8H2Br3NO4)(C14H14N4O2)(H2O)2]·H2O} n , (2), using the solution evaporation method. Both (1) and (2) were characterized by FT–IR spectroscopy, elemental analysis (EA), solid-state diffuse-reflectance UV–Vis spectroscopy, and powder and single-crystal X-ray diffraction analysis. Complex (1) shows a two-dimensional (2D) corrugated layer simplified as a 2D (4,4) topological network. The supramolecular interactions (π–π stacking, hydrogen bonding and C—Br...Br halogen bonding) play significant roles in the formation of an extended three-dimensional (3D) supramolecular network of (1). Complex (2) crystallizes in the chiral space group P212121 and exhibits a novel 3D homochiral framework, showing a diamond-like topology with Schläfli symbol 66. The homochirality of (2) is further confirmed by the solid-state circular dichroism (CD) spectrum. The second harmonic generation (SHG) property of (2) was also investigated. The hydrogen and C—Br...Br/O halogen bonding further stabilize the framework of (2). The central ZnII ions in (1) and (2) show tetrahedral and octahedral coordination geometries, respectively. The coordinated and uncoordinated water molecules in (2) could be removed selectively upon heating. Most importantly, (1) and (2) show rapid and highly sensitive sensing for a large pool of nitroaromatic explosives (NAEs).

Sensitive and rapid detection of aliphatic amines in water using self-stabilized micelles of fluorescent block copolymers

A kind of self-stabilized micelles of fluorescent block copolymers are constructed for rapid and sensitive detection of aliphatic amines in water based on capture-report strategy. An amphiphilic triblock copolymer functionalized with aggregation induced emission (AIE) chromophores self assembles into micelles with core-shell structures in aqueous solution. Hydrophobic AIE chromophores organize into cores, where hydrophobic interaction among the AIE chromophores inhibits the micelles from disassembling. The cores of AIE chromophores are surrounded by a corona of water-soluble polymer segments, endowing the micelles with superior dispersibility in water. Water-soluble polymer segments capture organic amines in water due to preferential hydrophobic interactions between them. The enriched amines in the corona subsequently diffuse into hydrophobic cores of micelles, quenching fluorescence of the AIE chromophores. The fluorescent micelles allow rapid detection of aliphatic amines in the order of seconds at a concentration as low as 8 μg/L.

Anion-Induced Structural Diversity of Zn and Cd Coordination Polymers Based on Bis-9,10-(pyridine-4-yl)-anthracene, Their Luminescent Properties, and Highly Efficient Sensing of Nitro Derivatives and Herbicides

Luminescent coordination polymers (CPs) of Zn²⁺ or Cd²⁺ and bis-9,10-(pyridine-4-yl)-anthracene (BA) show different 1D and 2D topologies depending on the anion used in the precursor. Compounds {[Zn(μ₂-BA)(MeOH)₂(p-Tos)₂]} _n (1) and {[Zn(μ₂-BA)(MeOH)₂(CF₃CO₂)₂]} _n (2) form linear structures and {BA@[Zn(μ₂-BA)(MeOH)₂(H₂O)₂](CF₃SO₃)₂} _n (3) featuring intercalation of uncoordinated BA molecules into linear ribbons. Cd-based CPs {[Cd(μ₂-BA)₂(ClO₄)₂]· n(DCM)} _n (4) and {[Cd(μ₂-BA)(MeOH)₂(Dioxane)(η₂-SiF₆)]·mDioxane} _n (5) form porous structures with 2D lattices. All complexes exhibit strong blue emission in the solid state with average lifetimes between 8 and 13 ns. The emission of compound 4 is sensitive to the presence of nitro aromatics, simazine, and trichloroanisole (TCA) and demonstrates nonlinear Stern-Volmer quenching kinetics. Limits of detection (LOD) of 15 and 16 ppb for picric acid and TCA were achieved, respectively.

Multicomponent Porphyrin-Based Tetragonal Prismatic Metallacages and their Photophysical Properties

Multicomponent coordination-driven self-assembly has proved to be a convenient approach to prepare advanced supramolecular coordination complexes (SCCs), especially for those with three-dimensional structures. Herein, we report the preparation of three tetragonal prismatic cages via the self-assembly of Pt(PEt₃)₂(OTf)₂, three different linear dipyridyl ligands and porphyrin-based sodium benzoate ligands. Due to the efficient charge separation in the coordination process of Pt(PEt₃)₂(OTf)₂ with pyridine and carboxylic acid and the directionality of metal-coordination bonds, these cages were prepared in high isolated yields (more than 90%). The absorption and emission properties as well as the singlet oxygen quantum yields of these cages were also studied, showing their potential applications as contrast agents for bio-imaging and photosensitizers for photodynamic therapy.

Heterobimetallic (FeII/PtII)-Based Supramolecular Coordination Complexes Using 1,1'-Ferrocene Dicarboxylate: Self-Assembly and Interaction with Carbon Dots

The synthesis and characterization of a new pyrazine-based ditopic organoplatinum(II) complex having a bite angle of 180° is reported. The facile and efficient syntheses are described of three discrete neutral Fe(II)/Pt(II) heterobimetallic SCCs with Pt(II) acceptor clips of different binding angles, 0, 120, and 180°. These new SCCs were characterized by multinuclear NMR and mass spectrometry. Electrochemical response of these ferrocene containing self-assembled ensembles was studied using cyclic voltammetry. The diplatinum acceptor organometallic clips significantly quench the fluorescence of highly emitting carbon quantum dots (CD), while the self-assembled macrocycles tend to nullify the quenching effect of the organometallic clips. Interestingly, the inefficient quenching of CD fluorescence by these SCCs was found to be directly related to the angular disposition of the binding sites in the Pt(II) based organometallic clips.

Porphyrin-functionalized coordination star polymers and their potential applications in photodynamic therapy

We present a new family of porphyrin-functionalized coordination star polymers prepared through combination of coordination-driven self-assembly and post-assembly polymerization. Their self-assembly behaviour in water and potential for photodynamic therapy were demonstrated.

Conversion of 12-membered d3- and l3-CoIII3CdII3 metallorings into a 24-membered d3l3-CoIII6CdII6 metalloring

A unique example of a heterometallic coordination system, in which metalloring sizes are controlled via homochirality vs. heterochirality, is reported.

Self-Assembly of Metallacages into Multidimensional Suprastructures with Tunable Emissions

Cubic metallacages were arranged into multidimensional (one-, two-, and three-dimensional) suprastructures via multistep assembly. Four new shape-controllable, hybrid metallacages with modified substituents and tunable electronic properties were prepared using dicarboxylate ligands with various substituents (sodium sulfonate, nitro, methoxyl, and amine), tetra-(4-pyridylphenyl) ethylene, and cis-(PEt3)2Pt(OTf)2. The as-prepared metallacages were used as building blocks for further assembly. Diverse suprastructures with tunable emissions (λmax from 451 to 519 nm) and various substituents (-SO3Na, -NO2, -OCH3, and -NH2) were prepared depending on the substituents and solvents used.

Fluorometric detection of nitroaromatics by fluorescent lead complexes: A spectroscopic assessment of detection mechanism

Three Schiff base ligands such as 2‑[(2‑Hydroxy‑3‑methoxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL1), 2‑[(2‑Hydroxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL2), 2‑[(3,5‑Dichloro‑2‑hydroxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL3) have been synthesized by condensation of aldehydes (such as 3,5‑Dichloro‑2‑hydroxy benzaldehyde, 2‑Hydroxy‑benzaldehyde, and 2‑Hydroxy‑3‑methoxy‑benzaldehyde) with Tris‑(hydroxymethyl)amino methane and characterized by IR, UV-vis and ¹H NMR spectroscopy. Then all these three ligands have been used to prepare Pb(II) complexes by reaction with lead(II) acetate tri-hydrate in methanol. In view of analytical and spectral (IR, UV-vis and Mass) studies, it has been concluded that, except HL2, other two ligands form 1:1 metal complexes (1 and 3) with lead. Between two complexes, complex 3 is highly fluorescent and this property has been used to identify the pollutant nitroaromatics. Finally, the quenching mechanism has been established by means of spectroscopic investigation.

Size-Selective Detection of Picric Acid by Fluorescent Palladium Macrocycles

This work presents the synthesis and characterization of two palladium-based fluorescent macrocycles offering hydrogen-bonding cavities of contrasting dimensions. Both palladium macrocycles function as chemosensors for the detection of nitroaromatics, whereas the larger macrocycle not only illustrates nanomolar detection of picric acid but also transports its significant amount from an aqueous to an organic phase.

Proton triggered emission and selective sensing of 2,4,6-trinitrophenol using a fluorescent hydrosol of 2-phenylquinoline

Compound 2-phenylquinoline (PhQ) displayed novel aggregation induced emission enhancement (AIEE) characteristics in its aggregate/solid state. It allows reversible fluorescence switching in acidic and basic media and ‘turn off’ fluorescence sensor for TNP.

Coordination driven self-assembly of [2 + 2 + 2] molecular squares: synthesis, crystal structures, catalytic and luminescence properties

Ten molecular squares were prepared through coordination-driven self-assembly and their catalytic activity and luminescence properties are reported.

A fluorescent cross-linked supramolecular network formed by orthogonal metal-coordination and host–guest interactions for multiple ratiometric sensing

A supramolecular network can be used for the ratiometric sensing of pH, cyclen and Cl⁻ due to the incorporation of two fluorophores and two non-covalent interactions.

A sensitive and selective sensor for picric acid detection with a fluorescence switching response

Low molecular weight organogelator for the detection of picric acid.

Platinum(II)-Based Convex Trigonal-Prismatic Cages via Coordination-Driven Self-Assembly and C60 Encapsulation

The development of three-dimensional (3D) supramolecular coordination complexes is of great interest from both fundamental and application points of view because these materials are useful in molecular catalysis, separation and purification, sensing, etc. Herein, we describe the synthesis of two Klärner's molecular-clip-based tetrapyridyl donors, which possess a C-shaped structure as shown by X-ray analysis, and subsequently use them to prepare four convex trigonal-prismatic cages via coordination-driven self-assembly with two 180° diplatinum(II) acceptors. The cages are fully characterized by multinuclear NMR (³¹P and ¹H) analysis, diffusion-ordered spectroscopy, electrospray ionization time-of-flight mass spectrometry, and UV/vis absorption spectroscopy. Moreover, the incorporation of molecular-clip-based ligands provides these cages with free cavities to encapsulate fullerene C₆₀ via aromatic interactions, which may be useful for fullerene separation and purification. The studies described herein enlarge the scope of the platinum(II)-based directional bonding approach in the preparation of curved 3D metallacages and their host-guest chemistry.

Bulky Isopropyl Group Loaded Tetraaryl Pyrene Based Azo-Linked Covalent Organic Polymer for Nitroaromatics Sensing and CO2 Adsorption

An azo-linked covalent organic polymer, Py-azo-COP, was synthesized by employing a highly blue-fluorescent pyrene derivative that is multiply substituted with bulky isopropyl groups. Py-azo-COP was investigated for its sensing and gas adsorption properties. Py-azo-COP shows selective sensing toward the electron-deficient polynitroaromatic compound picric acid among the many other competing analogs that were investigated. Apart from its chemosensing ability, Py-azo-COP (surface area 700 m2 g-1) exhibits moderate selectivity toward adsorption of CO2 and stores up to 8.5 wt % of CO2 at 1 bar and 18.2 wt % at 15.5 bar at 273 K, although this is limited due to the electron-rich -N=N- linkages being flanked by isopropyl groups. Furthermore, the presence of a large number of isopropyl groups imparts hydrophobicity to Py-azo-COP, as confirmed by the increased adsorption of toluene compared to that of water in the pores of the COP.

Design Principles for the Optimization of Guest Binding in Aromatic-Paneled FeII4L6 Cages

A series of aromatic-paneled Fe^II₄L₆ cages was synthesized through iron(II)-templated subcomponent self-assembly of 2-formylpyridine and C₂-symmetric diamine building blocks having differing geometries, including many with a large degree of lateral offset between metal-binding sites. The new cages were characterized using X-ray crystallography, NMR spectroscopy, and mass spectrometry. Investigations of the guest binding properties of the cages provided insights into the structural factors important for the observation of guest binding. Both the size and arrangement of the aromatic panels were shown to be crucial for achieving effective encapsulation of large hydrophobic guests, including fullerenes, polycyclic aromatic hydrocarbons, and steroids, with subtle differences in the structure of subcomponents resulting in incommensurate effects on the binding abilities of the resulting hosts. Cages with large, offset aromatic panels were observed to be the most effective hosts as a result of a preference for a ligand conformation where the aromatic panels lie tangent to the edges of the tetrahedron, thus maximizing cavity enclosure.

Triphenylbenzene Sensor for Selective Detection of Picric Acid

A C ₃-symmetric triphenylbenzene based photoluminescent compound, 1,3,5-tris(4'-(N-methylamino)phenyl) benzene ([NHMe]₃TAPB), has been synthesized by mono-N-methylation of 1,3,5-tris(4'-aminophenyl) benzene (TAPB) and structurally characterized. [NHMe]₃TAPB acts as a selective fluorescent sensor for picric acid (PA) with a detection limit as low as 2.25 ppm at a signal to noise ratio of 3. Other related analytes (i.e. TNT, DNT and DNB) show very little effect on the fluorescence intensity of [NHMe]₃TAPB. The selectivity is triggered by proton transfer from picric acid to the fluorophore and ground-state complex formation between the protonated fluorophore and picrate anion through hydrogen bonding interactions. The fluorescence lifetime measurements reveal static nature of fluorescence quenching.

Hand-Held Femtogram Detection of Hazardous Picric Acid with Hydrophobic Ag Nanopillar SERS Substrates and Mechanism of Elasto-Capillarity

Picric acid (PA) is a severe environmental and security risk due to its unstable, toxic, and explosive properties. It is also challenging to detect in trace amounts and in situ because of its highly acidic and anionic character. Here, we assess sensing of PA under nonlaboratory conditions using surface-enhanced Raman scattering (SERS) silver nanopillar substrates and hand-held Raman spectroscopy equipment. The advancing elasto-capillarity effects are explained by molecular dynamics simulations. We obtain a SERS PA detection limit on the order of 20 ppt, corresponding attomole amounts, which together with the simple analysis methodology demonstrates that the presented approach is highly competitive for ultrasensitive analysis in the field.

Two uranyl heterocyclic carboxyl compounds with fluorescent properties as high sensitivity and selectivity optical detectors for nitroaromatics

Uranyl skeleton compounds showed high sensitivity and selectivity for the detection of nitroaromatics.

A Quantitative Study of the Effects of Guest Flexibility on Binding Inside a Coordination Cage Host

We have performed a systematic investigation of the effects of guest flexibility on their ability to bind in the cavity of a coordination cage host in water, using two sets of isomeric aliphatic ketones that differ only in the branching patterns of their alkyl chains. Apart from the expected increase in binding strength for C9 over C7 ketones associated with their greater hydrophobic surface area, within each isomeric set there is a clear inverse correlation between binding free energy and guest flexibility, associated with loss of conformational entropy. This can be parameterized by the number of rotatable C-C bonds in the guest, with each additional rotatable bond resulting in a penalty of around 2 kJ mol-1 in the binding free energy, in good agreement with values obtained from protein/ligand binding studies. We used the binding data for the new flexible guests to improve the scoring function that we had previously developed that allowed us to predict binding constants of relatively rigid guests in the cage cavity using the molecular docking programme GOLD (Genetic Optimisation of Ligand Docking). This improved scoring function resulted in a significant improvement in the ability of GOLD to predict binding constants for flexible guests, without any detriment to its ability to predict binding for more rigid guests.

Self-assembly of stable luminescent lanthanide supramolecular M4L6 cages with sensing properties toward nitroaromatics

We report here the first example of concentration-triggered helicate-to-tetrahedron transformation in supramolecular lanthanide edifices, along with their highly efficient and selective luminescence sensing properties toward PA at the ppb level.

Development of luminescent sensors based on transition metal complexes for the detection of nitroexplosives

The detection of nitro explosives by transition metal complexes/metallosupramolecules with their designs and sensing mechanisms are comprehensively reviewed.

Five-component trigonal nanoprism with six dynamic corners

The metallo-supramolecular trigonal prism P is based on five different components and three unlike dynamic coordination motifs: the heteroleptic phenanthroline–terpyridine complex [Zn(1)(4)]²⁺ (HETTAP), the heteroleptic phenanthroline–pyridine complex [Cu(2)(5A)]⁺ (HETPYP-I), and the pyridine → zinc(ii)–porphyrin interaction.

A porous two-dimensional Zn(ii)-coordination polymer exhibiting SC–SC transmetalation with Cu(ii): efficient heterogeneous catalysis for the Henry reaction and detection of nitro explosives

The 2D Zn(ii)-CP, 1Zn and its Cu-analogue 1Cu exhibit efficient catalytic activity for the Henry reaction. 1Zn can be utilized for detecting trace amounts of nitro explosives in DMSO.

A supramolecular Tröger's base derived coordination zinc polymer for fluorescent sensing of phenolic-nitroaromatic explosives in water

A Tröger’s base functionalized luminescent nanoscale Zn(II) coordination polymer (TB-Zn-CP) is synthesized and used as selective fluorescence sensor for phenolic nitroaromatics in water.

A V-Shaped 4-amino-1,8-napthalimide derived tetracarboxylic acid linker (L; bis-[N-(1,3-benzenedicarboxylic acid)]-9,18-methano-1,8-naphthalimide-[b,f][1,5]diazocine) comprising the Tröger's base (TB) structural motif was rationally designed and synthesised to access a nitrogen-rich fluorescent supramolecular coordination polymer. By adopting the straight forward precipitation method, a new luminescent nanoscale Zn(ii) coordination polymer (TB-Zn-CP) was synthesized in quantitative yield using Zn(OAc)₂·2H₂O and tetraacid linker L (1 : 0.5) in DMF at room temperature. The phase-purity of as-synthesised TB-Zn-CP was confirmed by X-ray powder diffraction analysis, infra-red spectroscopy, and elemental analysis. Thermogravimetric analysis suggests that TB-Zn-CP is thermally stable up to 330 °C and the morphological features of TB-Zn-CP was analysed by SEM and AFM techniques. The N₂ adsorption isotherm of thermally activated TB-Zn-CP at 77 K revealed a type-II reversible adsorption isotherm and the calculated Brunauer–Emmett–Teller (BET) surface area was found to be 72 m² g^–1. Furthermore, TB-Zn-CP displayed an excellent CO₂ uptake capacity of 76 mg g^–1 at 273 K and good adsorption selectivity for CO₂ over N₂ and H₂. The aqueous suspension of as-synthesized TB-Zn-CP showed strong green fluorescence (λ_max = 520 nm) characteristics due to the internal-charge transfer (ICT) transition and was used as a fluorescent sensor for the discriminative sensing of nitroaromatic explosives. The aqueous suspension of TB-Zn-CP showed the largest quenching responses with high selectivity for phenolic-nitroaromatics (4-NP, 2,4-DNP and PA) even in the concurrent presence of other potentially competing nitroaromatic analytes. The fluorescence titration studies also provide evidence that TB-Zn-CP detects picric acid as low as the parts per billion (26.3 ppb) range. Furthermore, the observed fluorescence quenching responses of TB-Zn-CP towards picric acid were highly reversible. The highly selective fluorescence quenching responses including the reversible detection efficiency make the nanoscale coordination polymer TB-Zn-CP a potential material for the discriminative fluorescent sensing of nitroaromatic explosives.

Immobilizing Tetraphenylethylene into Fused Metallacycles: Shape Effects on Fluorescence Emission

Herein, we describe the selective formation of a discrete fused metallarhomboid and a triangle by the careful control of the shape and stoichiometry of the building blocks. A tetraphenylethylene (TPE)-based tetrapyridyl donor is exploited as the bridging component, and coordination immobilization of the TPE unit within the rigid metallacyclic frameworks efficiently suppresses its intramolecular rotational motions. As a result, the fused polygons are innately emissive in dilute solution, representing an alternative to aggregation-induced emission. Upon further molecular aggregation, these metallacycles display aggregation-induced enhanced emissions. Interestingly, the fused rhomboid 7 shows a weaker fluorescence in dilute solutions relative to that of the fused triangle 8, while a reversal of emission intensities was observed in the aggregated state. These markedly different fluorescence efficiencies are likely due to the differences in the shapes of the fused polygons. Thus, this work shows that the properties of supramolecular coordination complexes can be affected by subtle structural factors, which can be controlled easily and precisely at the molecular level.