Incorporating Electron-Deficient Bipyridinium Chromorphores to Make Multiresponsive Metal-organic Frameworks

A viologen-based Cd(II) coordination polymer as a multifunctional platform for photochromism, chemochromism and a broad range of fluorescence pH sensing

A multi-responsive Cd(II) coordination polymer (1) has been constructed by introducing a viologen derivative as both the framework backbone and ligand side pendant. Notably, compound 1 exhibits intriguing properties, including photochromism, methanol-assisted photochromism and chemochromism to ammonia. Furthermore, compound 1 also displays fluorescence pH sensing ability in a wide pH range.

Water-Stable Cd-MOF with fluorescent sensing of Tetracycline, Pyrimethanil, abamectin benzoate and construction of logic gate

Due to the indiscriminate abuse of pesticides and antibiotics has caused serious threats to the environment and human and animal bodies, the detection of antibiotics and pesticides has attracted widespread attention in recent years. Herein, a novel 2D Cd (II)-MOF, [Cd(L)_0.5(1,2-bimb)] (Cd-L-1,2-bimb), [H₄L = 1, 1'-ethylbiphenyl -3, 3', 5, 5'- tetracarboxylic acid, 1, 2-bimb = 1, 2-bis[(1H-imidazol-1-yl) methyl] benzene] is synthesized. Cd-L-1,2-bimb has excellent stability in different organic solvents and in the range of pH 1.1-12.5. Cd-L-1,2-bimb exhibits high selectivity, high sensitivity, and fast luminescent response to pesticides [pyrimethanil (PTH, LOD = 2.2 μM) and abamectin benzoate (AMB, LOD = 2.39 μM)] and antibiotic contaminants tetracycline (TET, LOD = 0.13 μM). Cd-L-1,2-bimb displays discriminative fluorescence when detecting AMB and PTH, and is an implication logic gate. Finally, the possible detection mechanism of Cd-L-1,2-bimb toward different pollutants is also further investigated. This MOF-based multifunctional sensor opens up new prospects for environmental monitors.

Inter-Network Charge-Transfer Excited State Formation Within a Two-fold Catenated Metal-Organic Framework

Charge-transfer excited state (CTES) defines the ability to split photon energy into work producing redox equivalents suitable for photocatalysis. Here, we report inter-net CTES formation within a two-fold catenated crystalline metal-organic framework (MOF), constructed with two linkers, N,N'-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide (DPNDI) and 2,6-dicarboxynaphthalene (NDC). The structural flexibility puts two complementary linkers from two nets in a proximal position to interact strongly. Supported by the electrochemical and steady-state electronic spectroscopic data, this ground-state interaction facilitates forming CTES that can be populated by direct excitation. We map the dynamics of the CTES which persists over a few nanoseconds and highlight the utilities of such relatively long-lived CTES as enhanced conductivity of the MOF under light over that measured in dark and as a proof-of-the-principle test, photo-reduction of methyl viologen under white light.

Anion-Afforded Functions of Ionic Metal-Organic Frameworks: Ionochromism, Anion Conduction, and Catalysis

The exchangeable counterions in ionic metal-organic frameworks (IMOFs) provide facile and versatile handles to manipulate functions associated with the ionic guests themselves and host-guest interactions. However, anion-exchangeable stable IMOFs combining multiple anion-related functions are still undeveloped. In this work, a novel porous IMOF featuring unique self-penetration was constructed from an electron-deficient tris(pyridinium)-tricarboxylate zwitterionic ligand. The water-stable IMOF undergoes reversible and single-crystal-to-single-crystal anion exchange and shows selective and discriminative ionochromic behaviors toward electron-rich anions owing to donor-acceptor interactions. The IMOFs with different anions are good ionic conductors with low activation energy, the highest conductivity being observed with chloride. Furthermore, integrating Lewis acidic sites and nucleophilic guest anions in solid state, the IMOFs act as heterogeneous and recyclable catalysts to efficiently catalyze the cycloaddition of CO₂ to epoxides without needing the use of halide cocatalysts. The catalytic activity is strongly dependent upon the guest anions, and the iodide shows the highest activity. The results demonstrate the great potential of developing IMOFs with various functions related to the guest ions included in the porous matrices.

Cationic coordination polymers with thirteen-fold interpenetrating dia networks: selective coloration and ion-controlled photochromism

A novel Cd-based cationic coordination polymer (Cd-CCP) constructed using viologen derivatives, which exhibits an unusual thirteen-fold interpenetrating diamondoid network, has been synthesized. Notably, Cd-CCP displays selective and naked-eye distinguished coloration and ion-controlled photochromism towards halide anions.

Tetraphenylpyrazine-Based Manganese Metal-Organic Framework as a Multifunctional Sensor for Cu2+, Cr3+, MnO4-, and 2,4,6-Trinitrophenol and the Construction of a Molecular Logical Gate

A tetraimidazole-decorating tetraphenylpyrazine has been designed and utilized for the fabrication of a novel metal-organic framework (MOF), denoted as {Mn(Tipp)(A)₂}_n·2H₂O (TippMn, where Tipp = 2,3,5,6-tetrakis[4-[(1H-imidazol-1-yl)methyl]phenyl]pyrazine and A = deprotonation of 1,4-naphthalenedicarboxylic acid), through hydrothermal synthesis. Structural analysis reveals that TippMn possesses a 2-fold-interpenetrated 4,8-connected three-dimensional (3D) network with an unprecedented {4¹⁶·6¹²}{4⁴·6²} topology. Fluorescent spectral investigations indicate that TippMn shows discriminative fluorescence when treated by Cr³⁺ and Cu²⁺, giving an INHIBIT logical gate performance. Meanwhile, TippMn can be further used as a sensor for MnO₄^- and 2,4,6-trinitrophenol (TNP) by fluorescence quenching. Notably, the sensing processes toward Cu²⁺, Cr³⁺, MnO₄^-, and TNP are labeled with high selectivity and sensitivity, quick response, and good recyclability. It is anticipated that this MOF-based versatile sensor could shed light on the exploration of MOFs for fluorescent sensors, optical switches, etc.

Positive Cooperative Protonation of a Metal-Organic Framework: pH-Responsive Fluorescence and Proton Conduction

Positive cooperative binding, a phenomenon prevalent in biological processes, holds great appeal for the design of highly sensitive responsive molecules and materials. It has been demonstrated that metal-organic frameworks (MOFs) can show positive cooperative adsorption to the benefit of gas separation, but potential binding cooperativity is largely ignored in the study of sensory MOFs. Here, we report the first demonstration of positive cooperative protonation of a MOF and the relevant pH response in fluorescence and proton conduction. The MOF is built of Zr-O clusters and bipyridyl-based tetracarboxylate linkers and has excellent hydrolytic stability. It shows a unique pH response that features two synchronous abrupt turn-off and turn-on fluorescent transitions. The abrupt transitions, which afford high sensitivity to small pH fluctuations, are due to cooperative protonation of the pyridyl sites with a Hill coefficient of 1.6. The synchronous dual-emission response, which leads to visual color change, is ascribable to proton-triggered switching between (n, π*) and (π, π*) emissions. The latter emission can be quenched by electron donating anion-dependent through photoinduced electron transfer and ground-state charge transfer. Associated with cooperative protonation, the proton conductivity of the MOF is abruptly enhanced at low pH by two orders, but overhigh acid concentration is adverse because excessive anions can interrupt the conducting networks. Our work shows new perspectives of binding cooperativity in MOFs and should shed new light on the development of responsive fluorescent MOFs and proton conductive materials.

A bi-functionalized metal-organic framework based on N-methylation and Eu3+ post-synthetic modification for highly sensitive detection of 4-Aminophenol (4-AP), a biomarker for aniline in urine

4-Aminophenol (4-AP), which is a biomarker of aniline and represents the internal dose of aniline exposure in the human body, has attracted much attention for its detection in recent years. In this work, a bi-functionalized luminescent metal-organic framework (MOF), Eu@MOF-253-CH_3, is designed and prepared through encapsulating the methyl groups and the Eu³⁺ cations into MOF-253 based on post-synthetic modification strategy. This study shows that the bi-functionalized Eu@MOF-253-CH₃ can specifically recognize 4-AP upon luminescence quenching, while refraining from the interference of other coexisting species in urine. The Eu@MOF-253-CH₃ hybrid as a 4-AP sensor also displays excellent performances including high water tolerance, good pH-independent stability, fast response, great selectivity and elevated sensitivity (0.5 μg mL^-1) attributed to N-viologenized ligand. These results suggest the bi-functionalized Eu@MOF-253-CH₃ can act as a promising sensor to practically monitor 4-AP's concentrations in human urine system, and then to realize the screening and pre-diagnosis of human health. Moreover, the possible sensing mechanisms are further explored at length.

Chromic and Fluorescence-Responsive Metal-Organic Frameworks Afforded by N-Amination Modification

Sensory materials that show color and/or fluorescence changes in response to specific gases or vapors have important applications in many fields. Here, we report the postsynthetic preparation of novel sensory metal-organic frameworks (MOFs) and their multiple responsive properties. Through postsynthetic N-amination, the 2,2'-bipyridyl spacers in a Zr(IV) MOF are partially transformed into N-aminobipyridinium. The new MOF (Zr-bpy-A) shows chromic behavior toward ammonia and amines because the electron-deficient pyridinium groups form charge-transfer complexes with amino moieties. It also shows a unique chromic response to formaldehyde owing to the Schiff-base condensation with the N-amino groups. Furthermore, the N-amino group can be used to graft different polycyclic aromatic hydrocarbons, which endow the MOF with strong fluorescence of variable colors and afford a high-contrast fluorescence response to ammonia/amines and formaldehyde associated with the chromic response. The presence of the unquaternized bipyridyl group also leads to a fluorescence response to HCl. The multiple responsive behaviors hold appeal for applications in sensing, switching, and antifake marking, which are illustrated with a test paper and writing ink.

Photoinduced versus spontaneous host–guest electron transfer within a MOF and chromic/luminescent response

The MOF shows charge-transfer sensitized Eu(iii) emission and spontaneous/photoinduced guest-to-host electron transfer, which allow chromic and luminescent sensing of NH3 (luminescence turn-off) and O2 (luminescence turn-on).

Dual functions of pH-sensitive cation Zr-MOF for 5-Fu: large drug-loading capacity and high-sensitivity fluorescence detection

Nanomaterials, as carriers of small molecular drugs, have been a focal point in recent years. In this work, a carbazolyl functionalized metal-organic framework, UiO-67-CDC, was successfully synthesized employing the ligand 9H-carbazole-2,7-dicarboxylic acid (9H-2,7-CDC). Postsynthetic approaches targeted the cationization and replacement of the Lewis base carbazole site with two methyl groups, resulting in the positively charged skeleton, which has proven to be a promising carrier for the anticancer drug 5-fluorouracil (5-Fu). The prepared cationic framework UiO-67-CDC-(CH3)2 showed moderately high surface area, hierarchical pore structures, and positive surface characteristics, which effectively and selectivity encapsulated the electron-rich 5-Fu molecules through electrostatic attraction, with a relatively high loading of up to 56.5% (wt%). The drug delivery in simulated blood environment (pH = 7.4) exhibited a more effective release, demonstrating a physiological pH-responsive sustained release. Significantly, the electron-deficient Zr-MOF itself, as a kind of high-sensitivity fluorescence detector, has a unique fluorescence "turn-on" effect with 5-Fu. These results pave the way towards designing surface-engineered MOF materials of interest in drug delivery and fluorescent sensing applications.

Effects of π-conjugation on the solid-state photoresponsive coloring behavior of bipyridine-boronium complexes

Solid-state photoinduced coloring of boronium complexes consisting of 9-borabicyclononane and 2,2'-bipyridine with π-conjugated substituents at the 4,4'- or 5,5'-positions was investigated. The substitution position affected the highest occupied molecular orbital distribution and determined the coloring capability. The 4,4'-substituted complexes exhibited coloration upon irradiation, whereas most of the 5,5'-substituted complexes did not.

Distinct and Selective Amine- and Anion-Responsive Behaviors of an Electron-Deficient and Anion-Exchangeable Metal-Organic Framework

Smart materials that respond to chemical stimuli with color or luminescence changes are highly desirable for daily-life and high-tech applications. Here, we report a novel porous metal-organic framework (MOF) that shows multiple, selective, and discriminative responsive properties owing to the combination of different functional ingredients [tripyridinium chromogen, Eu(III) luminophore, cationic framework, and special porous structure]. The MOF contains two interpenetrated three-dimensional cationic coordination networks built of a tetrahedral [Eu₄(μ₃-OH)₄] cluster and a tripyridinium-tricarboxylate zwitterionic linker. It shows reversible and discriminative chromic response to aliphatic amines and aniline through different host-guest interactions between electron-deficient pyridinium and electron-rich amines. The size- and shape-selective response to aliphatic amines is ascribed to the radical formation through host-guest electron transfer, whereas the response to aniline is ascribed to the formation of sandwich-type acceptor-donor-acceptor complexes. The MOF is capable of reversible anion exchange with various anions and shows selective and discriminative ionochromic response to iodide, bromide, and thiocyanate, which is attributed to charge-transfer complexation. The above chromic behaviors are accompanied by efficient quenching of Eu(III) photoluminescence. The MOF represents a multi-stimuli dual-output responsive system. It can be used for discrimination and identification of anions and amines. The potential use in invisible printing, reusable sensory films, and optical switches was demonstrated by the ink and the membrane made of the MOF and organic polymers.

Nanocage-Based InIII{TbIII}2-Organic Framework Featuring Lotus-Shaped Channels for Highly Efficient CO2 Fixation and I2 Capture

The exquisite combination of independent 3p [In(CO₂)₄] units and 4f [Tb₂(CO₂)₈] clusters in the presence of the designed hexatopic 2,4,6-tri(2,4-dicarboxyphenyl)pyridine ligand engenders one peculiar nanocaged In(III){Tb(III)}₂-organic framework: ({(Me₂NH₂)[InTb₂(HTDP)₂]·3DMF·3H₂O}_n, designated as NUC-5), which features dual types of lotus-shaped channels along the [100] and [110] axes with related node windows of 5.3 × 6.8 and 12.1 × 9.2 Ų, respectively. To the best of our knowledge, except several coexisted 3p-4f In/Ln clusters of {In₃Ln}- and {In₃Ln₂}-based metal-organic frameworks (MOFs), NUC-5 is one novel type of In/Ln heterometallic framework. In addition, its topology was an unprecedented 3D TAYZIC net with a Schläfli symbol of {4.⁴6²}{4.⁵6⁵}₂{4.⁶6.⁸8}. Moreover, activated NUC-5 is proved to be one efficient adsorbent for CO₂ and one recycled cycloaddition catalyst for the transformation of epoxides into related carbonates with high yields under mild conditions. Furthermore, the excellent reversible sorption performance for I₂ in the volatilization phase or in cyclohexane solution with a maximum adsorption capacity of 609.1 mg/g (3.75 iodine molecules per unit cell) makes NUC-5 a promising adsorbent for radioactive products of ¹²⁹I and ¹³¹I in the field of nuclear industry. This study provides one synthetic strategy that the original nature of MOFs could be enhanced by introducing some specific function-prompted inorganic subunits with the aid of predesigned supporting ligands.

Photoresponsivity and antibiotic sensing properties of an entangled tris(pyridinium)-based metal-organic framework

A two-dimensional Cd(ii) metal-organic framework (MOF) was constructed from a tris(pyridinium)-based hexacarboxylate zwitterionic ligand. The MOF shows a novel fashion of 2-fold 2D → 2D parallel entanglement. It is the entanglement that dictates close interlayer contacts between carboxylate (electron donor) and pyridinium (acceptor), which in turn impart the MOF with reversible photochromic properties through photoinduced electron transfer (PET). This is an extension of PET-based photochromism from bipyridinium to multipyridinium compounds. Thanks to the photoresponsive behaviour, the fluorescence of the MOF can be reversibly modulated or switched by photoirradiation. Besides, the fluorescence of the water-stable MOF in aqueous dispersion is very sensitive to nitrofuran antibiotics with high selectivity, and therefore the MOF is a good candidate of efficient and regenerable sensing material for determination of the antibiotics in water media.

A white-light-emitting lanthanide metal–organic framework for luminescence turn-off sensing of MnO4− and turn-on sensing of folic acid and construction of a “turn-on plus” system

A white-light-emitting lanthanide MOF shows recyclable and dual-responsive sensing for MnO₄⁻ and folic acid in an aqueous system with high selectivity and sensitivity.

The role of photoinduced charge transfer for photocatalysis, photoelectrocatalysis and luminescence sensing in metal–organic frameworks

Understanding PCT taking place within MOFs is crucial for designing porous photo/electrocatalysts and luminescent sensors. Unique features of PCT in MOFs and recent progress along with state-of-the-art characterization methods are discussed in the context of its applications.

Fluorescence Turn-On Response Amplified by Space Confinement in Metal-Organic Frameworks

Sensitive fluorescence turn-on response to specific substances is highly desired for development of chemical sensors and switches. Here we utilized a "two-in-one" strategy to prepare ionic metal-organic frameworks (MOFs) functionalized with the cationic bipyridinium receptors at the frameworks and anionic fluorescent indicators in the pores. The MOFs are rendered a fluorescence-resting state because the indicator's fluorescence is efficiently quenched by the ground-state charge-transfer (CT) complexation between the indicator and receptor. Addition of an alkylamine efficiently turns on the fluorescence because the indicator is displaced by the CT complexation between alkylamine with receptor. The turn-on response is highly specific to alkylamines. The MOFs can be used as recyclable sensors for selective and sensitive detection of alkylamines, with ultralow detection limits (0.5 nM). The fluorescence in solid state can be reversibly switched on and off with high contrast. The sensitive and high-contrast response can be attributed to the space confinement effects of the porous frameworks. The confined space can significantly enhance indicator-receptor and analyte-receptor interactions, and thereby both the quenching efficiency in the off state and the displacement efficiency in the on state are amplified.

MIL-61 and Eu3+@MIL-61 as Signal Transducers To Construct an Intelligent Boolean Logical Library Based on Visualized Luminescent Metal-Organic Frameworks

MIL-61 and its postsynthesis product (Eu³⁺@MIL-61) are employed as signal transducers to construct a series of basic logic gates (NOT, NAND, INHIBIT, and XNOR) on account of their simple synthetic process and fascinating luminescent properties. Also, a two-output combinational logic gate and a cascaded logic gate can be constructed on these two signal transducers by changing the inputs. In this logic gate library system, the fluorescence of MIL-61 (λ_395nm) or Eu³⁺@MIL-61 (λ_615nm) is used as outputs with a threshold of 0.5. The advantage of this boolean logical library is that the two signal transducers are readily available and cost effective. In addition, the luminescence change is visible to the naked eye under a UV lamp, which is more convenient in application. More importantly, it presents a new route for the design of a molecular logic gate library based on luminescent metal-organic frameworks. And for further application, we experimentally construct two logic devices (a 4-to-2 encoder and a parity checker) based on Eu³⁺@MIL-61 to perform nonarithmetic information.

Fabrication of a Luminescence-Silent System Based on a Post-Synthetic Modification Cd-MOFs: A Highly Selective and Sensitive Turn-on Luminescent Probe for Ascorbic Acid Detection

A unique three-dimensional luminescent metal-organic framework (Cd-MOFs), [Cd(tpbpc)₂]·2H₂O·DMF (Htpbpc = 4'-[4,2';6',4″]-terpyridin-4'-yl-biphenyl-4-carboxylic acid; DMF = dimethylformamide), was synthesized and structurally characterized; it exhibits excellent luminescent property and structural stability in aqueous solutions. Interestingly, an unparalleled luminescence-silent system CrO₄^2-@Cd-MOFs was successfully fabricated by postsynthetic modification of metal-organic frameworks. This luminescence-silent system represents a highly selective and sensitive turn-on luminescent responding to ascorbic acid. First, this advanced fluorescent sensor displays excellent performance for CrO₄^2- ions with a quenching of fluorescence intensity originating from fluorescence resonance energy transfer (FRET) mechanism. What's more, the fluorescent intensity of CrO₄^2-@Cd-MOFs system can be recovered (turn-on) for sensing ascorbic acid because of the elimination of FRET process. Such a novel fabrication strategy should offer the guidance to develop various MOFs-implicated luminescence-silent systems as "turn-on" sensors for detection of specific chemicals.

Space-confined indicator displacement assay inside a metal-organic framework for fluorescence turn-on sensing

The indicator displacement assay (IDA) is for the first time performed within a metal-organic framework (MOF) to achieve ultrasensitive fluorescence turn-on sensing. A Zr(iv) ion MOF (UiO-67-DQ-PsO) furnished with electron-deficient diquat units (DQ2+, as the receptor) on the wall and electron-rich 1-pyrenesulfonate anions (PsO-, as the fluorescent indicator) in the pores was prepared by postsynthetic anion exchange. The MOF is capable of sensing alkylamines owing to the competing PsO--DQ2+ and alkylamine-DQ2+ charge-transfer interactions, the former interaction causing a fluorescence OFF state and the latter displacing PsO- to trigger its emission. Significant advantages have been demonstrated for the IDA inside the MOF. The turn-on assay exhibits much higher sensitivity and anti-interference than the turn-off sensing using the MOF without indicators (the sensitivity is enhanced by as much as six orders of magnitude to the subnanomolar level). The integration of both the receptor and indicator in the porous solid enables facile regeneration and recyclability of the IDA ensemble. Furthermore, we show that the confined space provided by the MOF significantly enhances the supramolecular interactions to make possible the IDA impossible in solution. This work not only demonstrates a novel conceptual approach to fabricate superior fluorescence turn-on sensors using porous materials but also has important implications for supramolecular chemistry in porous materials.

Guest-Selective Recognition in a Flexible Bipyridinium-Based Framework in a Reversible Crystal-to-Crystal Fashion

A flexible bipyridinium-linker-based porous host framework with electron-accepting pore surface, namely, [Zn₂ (L)(pmc)_1.5 ]⋅12 H₂ O (1; L⋅Cl₂ =1,1'-[1,4-phenylene-bis(methylene)]bis(4,4'-bipyridinium) dichloride, H₄ pmc=pyromellitic acid) exhibits recognition of phenol and aromatic amine guests based on adsorbent-adsorbate charge-transfer interactions. Significantly, the resultant guest-encapsulated complexes 1@Guests can all be characterized by single-crystal X-ray diffraction. The host framework undergoes a reversible single crystal-to-single crystal transformation in response to the inclusion of different guests with flexible torsional motions of the hexagonal ring and the trapezoid-shaped bipyridinium groups. Such recognition can be visibly monitored and detected by obvious color changes. The host framework could also be recovered, and this suggested that guest sorption/desorption is reversible and that the host framework could be reused in potential applications. This work may provide an effective way to develop porous materials with special emphasis on applications involving guest recognition.

Guest-Induced Ultrasensitive Detection of Multiple Toxic Organics and Fe3+ Ions in a Strategically Designed and Regenerative Smart Fluorescent Metal-Organic Framework

Luminescent metal-organic frameworks (LMOFs) are promising functional materials for sustainable applications, where an analyte-induced multiresponsive system with good recyclability is beneficial for detecting numerous lethal pollutants. We designed and built the dual-functionalized, three-dimensional Zn(II)-framework [Zn₃( bpg)_1.5( azdc)₃]·(DMF)_5.9·(H₂O)_1.05 (CSMCRI-1) using an -OH group-integrated bpg linker and a -N═N- moiety containing H₂ azdc ligand, which functions as a unique tetrasensoric fluorescent probe. The activated CSMCRI-1 (1') represents the hitherto unreported pillar-layer framework for extremely selective fluorescence quenching by nitrofurazone antibiotics as well as explosive nitro-aromatic 2,4,6-trinitrophenol, where ultrasensitive detection is achieved for both the electron-lacking analytes. Impressively, 1' represents the first ever MOF for significant fluorescence "turn-on" detection of toxic and electron-rich 4-aminophenol in the concurrent presence of isomeric analogues. Density functional theory calculations highlight the specific importance of pillar functionalization in the "turn-on" or "turn-off" responses of 1' by electronically divergent toxic organics and provide further proof of supramolecular interactions between the framework and analytes. The fluorescence intensity of 1' dramatically quenches by a trace amount of Fe³⁺ ions over other competing metal ions, alongside visible colorimetric change of the framework in solid and solution phase upon Fe³⁺ encapsulation. The sensing ability of 1' remains unaltered for multiple cycles toward all lethal pollutants. The sensing mechanism is attributed to both dynamic and static quenching as well as resonance energy transfer, which strongly comply with the predictions of theoretical simulations. Considering the long-term and real-time monitoring, AND as well as OR molecular logic gates are constructed based on the discriminative fluorescence response for each analyte that provides a platform to fabricate smart LMOFs with multimode logic operations.

A metal–organic framework constructed by a viologen-derived ligand: photochromism and discernible detection of volatile amine vapors

A Co(ii)-MOF based on a viologen-derived ligand was obtained: the Co(ii) compound exhibits photochromism, and allows the visual and differentiable detection of different volatile alkylamines.

A silicotungstate-based copper–viologen hybrid photocatalytic compound for efficient degradation of organic dyes under visible light

An efficient visible light responsive compound [Cu(PBPY)]₂[SiW₁₂O₄₀] (1) has been constructed by integrating a silicotungstate cluster into the copper–viologen framework. It shows high photocatalytic efficiency for the degradation of dye pollutants.

Luminescent Hybrid Membrane-Based Logic Device: From Enantioselective Discrimination to Read-Only Memory for Information Processing

Logic circuit device and molecular computer are idealized binary tools that implement manifold signal transformation and operation and is a basic component of integrated circuits and is widely used in computer, computerized numerical control, and communication fields. By combining the advantages of synthetic feasibility and enantioselective luminescent recognition, a logic device based on the lanthanide functional membrane has been constructed to effectively recognize the enantiomer and judge the enantiomer excess of the chair drug mixture. In addition, it would be interesting if such a logic circuit could be assembled into a loop circuit to realize intelligent control of the electronic component. Read-only memory arrays built by the logic circuit are also actualized, which can be converted and stored in binary strings. This work provides an active and universal approach to modulate a luminescent device and logic circuit based on a chemical sensor, with promising application for intelligent control, information processing, and human-machine interaction.

Differentiable Detection of Volatile Amines with a Viologen-Derived Metal-Organic Material

The development of selective sensing materials for amine detection has received considerable attentions because amines have high toxicity and exist widely. In this article, we demonstrate for the first time that a degree of discriminative detection of alkylamines can be achieved by a metal-organic coordination material. The material is derived from Cd^II and 4,4'-bipyridinium-1,1'-bis(phenylene-3-carboxylate), shows 1D channels lined with electron-deficient viologen chromophores, and exhibits different colors upon contact with amine vapors of different molecular sizes and types (primary, secondary, and tertiary). The vapochromism is attributable to electron transfer from the amine group to viologen. The discrimination between amines is because the analyte-receptor interactions, which either directly mediate or indirectly affect electron transfer, are influenced by the number of the N-H bonds in the amine molecule, the size of the amine molecule relative to the receptor channel and the steric hindrance for the electron donor-acceptor contacts. The material also shows reversible photo- and hydrochromism owing to stimuli-induced reversible electron transfer. The compound can be deposited in paper simply by spraying the mixture solution of the starting metal salt and the ligand. The paper can be used as portable test strips for visual and differentiable detection of amines and as erasable inkless printing medium.

Five monocyclic pyridinium derivative based halo-argentate/cuprate hybrids or iodide salts: influence of composition on photochromic behaviors

Using novel monocyclic pyridinium derivatives as structural directing agents and electron acceptors, five composition dependent photochromic compounds have been synthesized.