Multiple Electron Transfer in Semiconductive Ternary D-D'-A Metal-Organic Framework for Enhanced X-Ray Detection and Imaging

Semiconductive metal-organic frameworks (MOFs) with donor-acceptor (D-A) characteristics have garnered attractive attention due to their capacity for separating and transferring photogenerated charges, making them promising candidates for high-performance X-ray detectors. However, the low charge transfer efficiency between the metal nodes and organic ligands limits the X-ray-to-electricity conversion efficiency of these materials. Herein, an additional photoactive donor (D') is introduced by incorporating a heavy atom-containing polyoxometalate (POM) [α-SiW12O40]4- into a binary {[Ni·bcbp·(H2O)2]·(H2O)4·Cl}n (Ni-bcbp, bcbp: H2bcbp·2Cl = 1,1'-bis(4-carboxyphenyl)(4,4'-bipyridinium) dichloride) MOF, resulting in a semiconductive ternary D-D'-A framework {[Ni2(bcbp)2·(H2O)4·(DMA)]·(SiW12O40)}n (SiW@Ni-bcbp, DMA: dimethylacetamide). The obtained material features an unprecedented porous 8-connected bcu-net structure that accommodates nanoscale [α-SiW12O40]4- counterions, displaying uncommon optoelectronic responses. In contrast to binary Ni-bcbp, the SiW@Ni-bcbp framework exhibits distinctive photochromism and robust X-ray responsiveness, which can be attributed to the synergistic effects of the electron reservoir and multiple photoinduced electron transfer originating from the POMs. As a result, the X-ray detector based on SiW@Ni-bcbp demonstrates a sensitivity of 5741.6 µC Gyair -1 cm-2 with a low detection limit of 0.49 µGyair s-1. Moreover, the devices demonstrated the capability of producing clearness X-ray images, providing a feasible and stable solution for constructing high-performance direct X-ray detectors.

Semiconductive Potassium Hydroxamate Coordination Polymers with Dual Charge Transport Paths Originating from the π-π Stacking Columns

Semiconductive coordination polymers (CPs) have recently garnered a significant amount of attention due to their widespread application in many areas. The "through-space" approach has emerged as the most versatile strategy for constructing semiconductive CPs. However, this approach often leads to the formation of unidirectional charge transport paths, resulting in anisotropic electrically conductive performance and low average conductivities in pressed pellets, thus presenting significant challenges for the practical application of semiconductive CPs. Consequently, there is a strong desire to explore simpler and more versatile strategies for designing semiconductive CPs with dual or multiple charge transport paths. Herein, we report on two semiconductive potassium hydroxamate coordination polymers, denoted as [K(HONDI)(H2O)2]n (1) and [K(HONDI)]n (2). Both compounds theoretically possess dual charge transport paths, occurring internally and externally within the π-π stacking columns of the ligands. Conductivity measurements revealed that compounds 1 and 2 both exhibit semiconductive properties, with their electrical conductivities reaching 2.3 × 10-6 and 1.9 × 10-7 S/cm, respectively, at 30 °C. Their electrically conductive performance could be attributed to theoretically biaxial "band-like" charge transport inside crystals and "hopping" charge transport between grain boundaries.

Bismuth Telluride Supported Sub-1 nm Polyoxometalate Cluster for High-Efficiency Thermoelectric Energy Conversion

Size plays a crucial role in chemistry and material science. Subnanometer polyoxometalate (POM) clusters have gained attention in various fields, but their use in thermoelectrics is still limited. To address this issue, we propose the POM clusters as an effective second phase to enhance the thermoelectric properties of Bi0.4Sb1.6Te3. Thanks to their subnanometer size, POM clusters improve electrical transport behavior through the superposition of atomic orbitals and the interfacial scattering effect. Furthermore, their ultrasmall size strongly reduces thermal conductivity. Consequently, the introduction of a mere 0.1 mol % of POM into the Bi0.4Sb1.6Te3 matrix realizes a state-of-the-art zT value of 1.46 at 348 K, a 45% enhancement over Bi0.4Sb1.6Te3 (1.01), along with a maximum thermoelectric-conversion efficiency of the integrated module of 6.0%. The enhancement of carrier mobility and the suppression of thermal conduction achieved by introducing the subnanometer clusters hold promise for various applications, such as electronic devices and thermal management.

Photothermal Conversion Perylene-Based Metal-Organic Framework with Panchromatic Absorption Bandwidth across the Visible to Near-Infrared

Recently, facilely designable metal-organic frameworks have gained attention in the construction of photothermal conversion materials. Nonetheless, most of the previously reported photothermal conversion metal-organic frameworks exhibit limited light absorption capabilities. In this work, a distinctive metal-organic framework with heterogeneous periodic alternate spatial arrangements of metal-oxygen clusters and perylene-based derivative molecules was prepared by in situ synthesis. The building blocks in this inimitable structure behave as both electron donors and electron acceptors, giving rise to the significant inherent charge transfer in this crystalline material, resulting in a narrow band gap with excellent panchromatic absorption, with the ground state being the charge transfer state. Moreover, it can retain excellent air-, photo-, and water-stability in the solid state. The excellent stability and broad light absorption characteristics enable the effective realization of near-infrared (NIR) photothermal conversion, including infrequent NIR-II photothermal conversion, in this perylene-based metal-organic framework.

Noncovalent Dualism in Perylene-Diimide-Based Keggin Anion Complexes: Theoretical and Experimental studies

We report the synthesis and comprehensive characterization of organic-inorganic hybrid salts formed by bis-cationic N,N'-bis(2-(trimethylammonium)ethylene)perylene-3,4,9,10-tetracarboxylic acid bisimide (PTCD2+) and Keggin-type [XW12O40]n- (X = Si, n = 4; X = P, n = 3) polyoxometalates. (PTCD)3[PW12O40]2·3DMSO·2H2O (2) and (PTCD)2[SiW12O40]·DMSO·2H2O (3) were structurally characterized by single crystal X-ray diffraction. The cations in both structures exhibited infinite chainlike arrangements through π-π interactions, contrasting with the previously reported cation-anion stacking observed in naphthalene diimide derivatives. A detailed theoretical study employing topological analysis of the electron density distribution within the quantum theory of atoms in molecules approach provided further insights into this structural dualism. Atomic force microscopy analyses revealed the formation of self-assembled supramolecular structures on graphite from molecular monolayers (3 nm of thick) to submicrometer aggregates for 2. Hyperspectral Raman spectroscopy imaging revealed that such heterostructures are likely formed by an enhanced π-π interactions. Both complexes demonstrated interesting electrochemical behavior, photoluminescence and X-ray-induced luminescence. Electron spin resonance analysis confirmed charge separation in both compounds, with enhanced efficiency observed in compound 2. Our findings of these perylene-based organic-inorganic hybrid salts offer the potential for their application in optoelectronic devices and functional materials.

Novel Semiconductive Ternary Hybrid Heterostructures for Artificial Optoelectronic Synapses

Synaptic devices that mimic biological synapses are considered as promising candidates for brain-inspired devices, offering the functionalities in neuromorphic computing. However, modulation of emerging optoelectronic synaptic devices has rarely been reported. Herein, a semiconductive ternary hybrid heterostructure is prepared with a D-D'-A configuration by introducing polyoxometalate (POM) as an additional electroactive donor (D') into a metalloviologen-based D-A framework. The obtained material features an unprecedented porous 8-connected bcu-net that accommodates nanoscale [α-SiW12 O40 ]4- counterions, displaying uncommon optoelectronic responses. Besides, the fabricated synaptic device based on this material can achieve dual-modulation of synaptic plasticity due to the synergetic effect of electron reservoir POM and photoinduced electron transfer. And it can successfully simulate learning and memory processes similar to those in biological systems. The result provides a facile and effective strategy to customize multi-modality artificial synapses in the field of crystal engineering, which opens a new direction for developing high-performance neuromorphic devices.

Selective Photochromic Response to Low-Dose X-ray Radiation Detection in One-Dimensional Cadmium-Viologen Complexes

Photochromic viologen-based materials have emerged as one of the most promising candidates for the development of X-ray light detection applications, including medical diagnosis and treatment, environmental radiation inspection, and industrial crack detection. However, the design and construction of low-dose X-ray-sensitive complexes remains an immense challenge, especially for the in-depth dissection of their response mechanisms. Herein, by using N,N'-4,4'-bipyridiniodipropionate (CV) as functional sensitive structural units and cadmium as heavy atoms, two cadmium-viologen complexes with one-dimensional chained structures, namely, [Cd₂Cl₄(CV)(H₂O)₂]_n (1) and [CdBr₂(CV)]_n (2), have been constructed, which exhibit a remarkable and selective photochromic response to low-dose X-ray radiation detection. Compound 1 is visually sensitive to both X-ray and UV light due to the more accessible photoinduced electron transfer (ET) pathways, while compound 2 only shows a slight color-changing process in response to UV light, in conformity with UV-vis absorbance analyses and kinetic studies. Surprisingly, compound 2 has longer ET pathways than 1, but not in response to high-energy X-ray light, seeming to contradict the previous phenomena. On further analysis, the key point in achieving X-ray-sensitive behavior should be a good balance among the electron donor-acceptor distance, intermolecular interaction, and X-ray absorbing capacity, as verified by density functional theory (DFT) and X-ray absorption strength calculations, X-ray photoelectron spectra, electron paramagnetic resonance measurements, and independent gradient model analysis. In particular, compound 1 is unprecedentedly sensitive to soft X-ray radiation, accompanied by an X-ray detection limit of as low as 2.91 Gy. These findings push forward the further development of low-dose X-ray sensing materials.

π-Stacks of radical-anionic naphthalenediimides in a metal-organic framework

Radical-ionic metal-organic frameworks (MOFs) have unique optical, magnetic, and electronic properties. These radical ions, forcibly formed by external stimulus-induced redox processes, are structurally unstable and have short radical lifetimes. Here, we report two naphthalenediimide-based (NDI-based) Ca-MOFs: DGIST-6 and DGIST-7. Neutral DGIST-6, which is generated first during solvothermal synthesis, decomposes and is converted into radical-anionic DGIST-7. Cofacial (NDI)₂^•- and (NDI)₂^2- dimers are effectively stabilized in DGIST-7 by electron delocalization and spin-pairing as well as dimethylammonium counter cations in their pores. Single-crystal x-ray diffractometry was used to visualize redox-associated structural transformations, such as changes in centroid-to-centroid distance. Moreover, the unusual rapid reduction of oxidized DGIST-7 into the radical anion upon infrared irradiation results in effective and reproducible photothermal conversion. This study successfully illustrated the strategic use of in situ prepared cofacial ligand dimers in MOFs that facilitate the stabilization of radical ions.

Solvent-Modulated Self-Assembly of Naphthalenediimide-Based Cd(II) Complexes and the Controllable Photochromism via Conformational Isomerization

Rational regulation of the properties of photochromic materials is a challenging and meaningful work. In the present work, NDI-based complexes, namely, [Cd_0.5(NDI)(HBDC)]·H₂O (1) and a series of conformational isomers of {[Cd(NDI)_0.5(BDC)]·MeCN}_n (2), were synthesized by varying the solvent conditions (H₂BDC = terephthalic acid, NDI = N,N'-bis(3-pyridylcarbonylhydrazine)-1,4,5,8-naphthalene diimide). Complex 1 exhibits a 0D mononuclear structure without photochromic behavior due to the bad conjugation of the naphthalene diimide moiety. The conformational isomers of complex 2 manifest a 3D network, showing ultra-fast photo-induced intermolecular electron transfer photochromic behavior under X-ray, UV, and visible light. However, they show different photochromic rates and coloring contrast upon photoirradiation, which originates from their difference in the distances of lone pair(COO)···π(NDI). This was realized via controlling the solvent ratio in the reaction system. In addition, compared to UV/X-ray light, 2 exhibits greater sensitivity to visible light and is an organic-inorganic hybrid material with photomodulated luminescence. Based on the excellent performance, complex 2 can be applied to filter paper, showing potential applications as an inkless printing medium and selective perception of ammonia and amine vapors in the solid state via different visual color changes.

Applications of Viologens in Organic and Inorganic Discoloration Materials

Viologen derived from 4,4'-bipyridine has attracted much attention because of its color changing properties with electron transfer, unique redox stability and structural diversity. These characteristics have led to its successful use in various applications, in particular in color-changing materials. In the past few years, researchers have been working on the syntheses of viologen-based color-changing functional materials, and such materials have been widely used in many fields. In photochromic materials, it is used as anti-counterfeiting material; in thermochromic, it is used as memory storage material, and in electrochromic, it is used as a battery material. This Review discusses the progress of viologen in organic and inorganic discoloration materials in recent years. The syntheses of viologen and its derivatives are summarized, and its application in the field of discoloration materials is introduced.

Donor-Acceptor Hybrid Heterostructures: An Emerging Class of Photoactive Materials with Inorganic and Organic Semiconductive Components

Just as the heterojunctions in physics, donor-acceptor (D-A) heterostructures are an emerging class of photoactive materials fabricated from two semiconductive components at the molecular level. Among them, D-A hybrid heterostructures from organic and inorganic semiconductive components have attracted extensive attention in the past decades due to their combined advantages of high stability for the inorganic semiconductors and modifiability for the organic semiconductors, which are particularly beneficial to efficiently achieve photoinduced charge separation and transfer upon irradiations. In this review, by analogy with the heterojunctions in physics, a definition of the D-A heterostructures and their general design and synthetic strategies are given. Meanwhile, the D-A hybrid heterostructures are focused on and their recent advances in potential applications of photochromism, photomodulated luminescence, and photocatalysis summarized.

A photochromic and scintillation Eu-MOF with visual X-ray detection in bright and dark environments

The detection of X-rays has always been a frontier of scientific research. An Eu-MOF with both X-ray-induced photochromic and scintillation properties has been synthesized through the combination of a photochromism-active viologen ligand and rare earth Eu element with high-efficiency absorption of X-rays. In a bright environment, Eu-MOF exhibits different color changes under high-energy X-rays and low-energy X-rays, which can effectively distinguish X-rays. Eu-MOF can also be used for X-ray detection by scintillation properties in dark environments. This work provides a new perspective on the design of multifunctional materials that can perform simple X-ray detection in different environments.

Reactive organic radical-doped Ag(I)-based coordination compounds for highly efficient antibacterial wound therapy

Antibiotics, being critical antimicrobial agents, have been widely used for treating bacterial infections. However, prolonged use of antibiotics can induce drug resistance resulting in "superbug" that threatens human health. Therefore, developing antibiotic-free materials with intrinsic antibacterial properties is the key to the "superbug" challenge. In this study, two highly efficient metal-organic frameworks (MOFs) were successfully assembled through synergistic use of the antibacterial properties of reactive organic radicals and silver (Ag) cations. These hybrid Ag-based materials possessed radical-doped characteristics, continuously releasing Ag⁺, which significantly inhibited the growth of four common Gram-negative and Gram-positive human pathogens (Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus aureus), and particularly two multi-drug-resistance bacteria (MRSA and MDR-PA). Furthermore, in vivo assays indicated that the synergistic antibacterial effect of these compounds could significantly accelerate the healing rate of infected wounds in mice. Blood biochemistry and histological analyses of main organs in treated mice also exhibited negligible cytotoxicity. This study unveiled the promising potential of Ag-MOFs for anti-infective therapies and future clinical applications.

Design of a Polyoxometalate-Based Metal-Organic Framework for Photocatalytic C(sp3)-H Oxidation of Toluene

A powerful and promising route for developing novel photocatalysts for light-driven toluene oxidation in water under mild conditions is presented. Herein, a novel polyoxometalate-based metal-organic framework (POMOF), {Co₄W₂₂-DPNDI}, is prepared by incorporating the unusual Co₄-sandwiched POM anion [Co₄(μ-OH)₂(SiW₁₁O₃₉)₂]^10- ({Co₄W₂₂}) and the photoactive organic bridging link N,N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI) into a framework. {Co₄W₂₂} is a good candidate for photocatalytic water oxidation. DPNDI is easily excited to form the radical species DPNDI* in the presence of an electron donor, which is beneficial for activation of the inert O₂. Anion···π interactions and covalent bonds between {Co₄W₂₂} and DPNDI facilitate electron-hole separation and electron transfer. {Co₄W₂₂-DPNDI} displays high catalytic activity for the activation of the C(sp³)-H bond of toluene using light as a driving force and inexpensive water as an oxygen source under mild conditions. In particular, the yield and selectivity are improved by replacing oxygen with water, which may be ascribed to the release of protons during the water oxidation process that facilitate the generation of ^•OH.

Ultrafast visible-light photochromic properties of naphthalenediimide-based coordination polymers for visual detecting/filtering blue light

Two novel naphthalenediimide-based (NDI-based) coordination polymers (CPs) [Cd∙(3-PMNDI)∙(HNDC)2∙(DMF)] (1) and [Cd∙(4-PMNDI)∙(NDC)]∙DMF (2) (H2NDC = 1,4-naphthalenedicarboxylic acid, 3-/4-PMNDI = N,N′-bis(3-/4-pyridylmethyl)-1,4,5,8-naphthalenediimide, DMF = N,N′-dimethylformamide), have been designed and synthesized, which are constructed...

Direct synthesis of a stable radical doped electrically conductive coordination polymer

K-ONDI, a directly synthesized coordination polymer, contains NDI˙− radicals that are stable in air and in common organic solvents. Benefiting from π–π interactions and unpaired electrons, K-ONDI exhibits an electrical conductivity of 10−6 S cm−1.

Photochromic Polyoxometalate/Perylenediimide Donor-Acceptor Hybrid Crystals with Interesting Luminescent Properties

The self-assembly of electron-deficient protonated N, N'-dipyridyltetrachloroperylenediimide (4Cl-DPPDI) and electron-rich polyoxometalate acids H_nXM₁₂O₄₀ (POMs; X = P or Si; M = W or Mo) resulted in four isomorphous donor-acceptor hybrid crystals 1-4 with segregated POM anions and one-dimensional racemic hydrogen-bonded 4Cl-DPPDI networks as electron-donor and -acceptor components, respectively. Because of the compact contacts between the POM anions and 4Cl-DPPDI tectons induced by anion-π interactions, besides enhanced photochromism, these four unique isostructural hybrids exhibited unusual room-temperature phosphorescence (RTP) emissions. More interestingly, owing to the facial compact contacts of two racemic 4Cl-DPPDI tectons induced by lone pair-π-assisted π-π interactions, they also showed unprecedented photon upconversion by triplet-triplet annihilation (TTA).

A Series of Polyoxometalate-Viologen Photochromic Materials for UV Probing, Amine Detecting and Inkless and Erasable Printing

In this work, by using two kinds of viologen ligands three POM-based Compounds were obtained under hydrothermal conditions, namely [Ag^I (bmypd)_0.5 (β-Mo₈ O₂₆ )_0.5 ] (1) (bmypd ⋅ 2Cl=1,1'-[Biphenyl-4,4'-bis(methylene)]bis(4,4'-bipyridyinium)dichloride), [Ag^I ₂ (bypy)₄ (HSiW₁₂ O₄₀ )₂ ] ⋅ 14H₂ O (2) and [Ag^I (bypy)(γ-Mo₈ O₂₆ )_0.5 ] (3) (bypy⋅Cl=1-Benzyl-4,4'-bipyridyinium chloride). The structures were characterized by Fourier transform infrared spectroscopy (FT-IR), Powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS) and single crystal X-ray diffraction. Compounds 1-3 show excellent photochromic ability with fast photoresponse under the irradiation of ultraviolet light with different degrees of color changes. So compounds 1-3 can be used as visible ultraviolet detectors. Compounds 1-3 also possess photoluminescence properties with fast and excellent fluorescence quenching effect. Compounds 1-3 also can be used as inkless and erasable printing materials with suspensions of 1-3 applied to filter paper. Compounds 1-3 can also produce color changes in amine vapor environment, especially in an NH₃ atmosphere. Compounds 1-3 can be used as organic amine detectors.

Radical-Doped Crystalline Lanthanide-Based Photochromic Complexes: Self-Assembly Driven by Multiple Interactions and Photoswitchable Luminescence

Stimuli-responsive functional materials, especially the light stimulation color change and tunable fluorescent materials, have received considerable attention because of their broad applications in smart materials. Herein, a series of lanthanide-based [Ln = Nd(III) (1), Sm(III) (2), Eu(III) (3), Gd(III) (4), Tb(III) (5), Yb(III) (6), and Lu(III) (7)] crystalline complexes were attained by simply adding the aqueous lanthanide nitrate solution to the water-soluble naphthalenediimide derivative. The obtained lanthanide-based crystalline materials not only show significant photochromism but also possess reactive organic radicals under ambient conditions. Intriguingly, photoswitchable near-infrared (NIR) fluorescence was realized in the crystalline complex 1. The structures of these crystalline materials were systematically studied to clarify the weak interaction-assisted charge-transfer process. The underlying multiple-interaction-assisted supramolecular self-assembly, the radical-doped nature, and the corresponding photochromic mechanism were thoroughly unearthed by single-crystal X-ray diffraction, in situ solid-state UV-vis diffuse reflectance, and electron paramagnetic resonance spectrometric analysis.

Exploring the structure-property schemes in anion-π systems of d-block metalates

Anion-π based compounds, materials, and processes have gained significant interest due to the diversity of their aesthetic non-covalent synthons, and thanks to their significance in biological systems, catalytic processes, anion binding and sensing, or the supramolecular organization of hierarchical architectures. While systems based on typical inorganic anions or organic residues have been widely reviewed in recent years, those involving anionic d metal comlexes as the main components have been treated with a rather secondary interest. However, actively exploring the new systems of the latter type we have recognized systematic advances in the field. As a result, in the current review we describe the landscape that has recently emerged. Focusing on the established groups of π-acidic species, i.e. polycarbonitirles, polyazines, polyazine N-oxides, diimide derivatives, fluoroarenes, and nitroarenes, we explore and discuss anion-π crystal engineering together with the structure-property schemes important from the standpoint of charge transfer (CT) and electron transfer (ET), magnetism, luminescence, reactivity and catalysis, and the construction of core-shell crystalline composites.

Multinuclear Lanthanide-Implanted Tetrameric Dawson-Type Phosphotungstates with Switchable Luminescence Behaviors Induced by Fast Photochromism

A series of benzoate-decorated lanthanide (Ln)-containing tetrameric Dawson-type phosphotungstates [N(CH₃)₄]₆H₂₀[{(P₂W₁₇O₆₁)Ln(H₂O)₃Ln(C₆H₅COO)(H₂O)₆]}{[(P₂W₁₇O₆₁)Ln(H₂O)₃}]₂Cl₂·98H₂O [Ln = Sm (1), Eu (2), and Gd (3)] were made using a facile one-step assembly strategy and characterized by several techniques. Notably, the Ln-containing tetrameric Dawson-type polyoxoanions [{(P₂W₁₇O₆₁)Ln(H₂O)₃Ln(C₆H₅COO)(H₂O)₆]}{[(P₂W₁₇O₆₁)Ln(H₂O)₃}]₂^24- are all established by four monolacunary Dawson-type [P₂W₁₇O₆₁]^10- segments, encapsulating a Ln³⁺ ion with two benzoates coordinating to the Ln³⁺ ions. 1-3 exhibit reversible photochromism, which can change from intrinsic white to blue for 6 min upon UV irradiation, and their colors gradually recover for 30 h in the dark. The solid-state photoluminescence spectra of 1 and 2 display characteristic emissions of Ln components based on 4f-4f transitions. Time-resolved emission spectra of 1 and 2 were also measured to authenticate the energy transfer from the phosphotungstate and organic chromophores to Eu³⁺. In particular, 1 shows an effectively switchable luminescence behavior induced by its fast photochromism.

Inter-ligand charge-transfer interactions in a photochromic and redox active zinc–organic framework

A novel Zn(ii)–organic framework with 1D stair-like structure displays reversible photochromic and redox active properties. And inter-ligands charge-transfer interactions exist in this material.

A square-shaped complex with an electron-acceptor ligand: unique cubic crystal symmetry and similarity to the inorganic mineral katoite

We successfully obtained a Pt square complex having an electron-accepting ligand, which shows a strong similarity to the high-pressure phase of the natural mineral katoite in the solid state.

A multifunctional colorimetric sensor originating from a cadmium naphthalene diimide-based metal–organic framework: photochromism, hydrochromism, and vapochromism

A new cadmium metal–organic framework with photocontrolled luminescence properties and multiple chromic properties was synthesized for used as a multifunctional colorimetric sensor and provide a new route to design functional MOFs.

A novel multichromic Zn(II) cationic coordination polymer based on a new flexible viologen ligand exhibiting aniline detection in the solid state

In this work, a novel multichromic cationic coordination polymer, named [Zn4(BTC)3(bcbpy)2]·5H2O (1), based on a new flexible viologen ligand 1,1'-bis(3-cyanobenzyl)-[4,4'-bipyridine]-1,1'-diium (H2bcbpy·2Cl), Zn(NO3)2·6H2O and pyromellitic acid (H4BTC) was synthesized. Compound 1 has good photosensitive activity and can respond to sunlight at room temperature. The colour of compound 1 changes rapidly in response to UV light and blue ray irradiation within 5 s. We rarely obtained the crystal structures after irradiation under UV light and blue ray. At the same time, compound 1 shows the hydrochromism phenomenon when heated at 120 °C, and it also shows the ability of detecting aniline and NO2- under low-concentration conditions (10-4 M).

Ultrastable radical-doped coordination compounds with antimicrobial activity against antibiotic-resistant bacteria

In the present work, we have introduced a series of stable radical-doped coordination compounds composed of donor-acceptor structures and shown to produce organic radicals in situ as a result of unconventional lone pair-π interactions in ambient conditions. Inconspicuous lone pair-π and C-Hπ interactions were shown to play a key role in self-assembly as well as the charge transfer process, resulting in a long-lived charge-separated state able to generate organic radicals. The resultant species displayed broad-spectrum antimicrobial activity, including against multi-drug-resistant bacteria. This study unveiled the promise of reactive organic radical-doped materials as a new platform for developing antimicrobial agents that can overcome antibiotic resistance.

Impact of diffusion methods and metal cations on photochromic three-component D-A hybrid heterostructures

D-A hybrid heterostructures are an attractive class of hybrid complexes composed of semiconducting organic and inorganic components, which make them potential candidates for applications in the photoelectric fields, particularly as photochromic materials. Herein, we report that the combination of metal cations (M = Zn2+ or Cd2+), silicomolybdic anions, and N,N-di(4-pyridyl)-1,4,5,8-naphthalene diimide (DPNDI) via two diffusion methods (A and B) led to four three-component D-A hybrid heterostructures with silicomolybdic anions as electron donors, and one-dimensional (1-D) naphthalenediimide coordination networks of different metal cations, [Zn2(DPNDI)2(H2O)4]·(SiMo12O40) (1-A and 1-B) and [Cd2(DPNDI)2(H2O)4]·(SiMo12O40) (2-A and 2-B), as electron acceptors. Although the different diffusion methods, 1-B, 2-A and 2-B, are isostructures with close cell parameters. Due to the different ionic radii and electronegativity of metal cations in isostructural 1-B and 2-B, they exhibit different electron-transfer photochromic behaviors. This study paves a new path for designing novel photochromic materials through such third-component metal cations.

The impact of positional isomerism on electronic and photochromic properties of 1D zinc-based naphthalene diimide coordination polymers

The positional isomeric DPNDI ligands can effectively modulate the interfacial contacts of electron donors/acceptors and the efficiency of electronic/photochromic properties.

Polyoxometalate–viologen photochromic hybrids for rapid solar ultraviolet light detection, photoluminescence-based UV probing and inkless and erasable printing

Polyoxometalate–viologen photochromic hybrids showed efficient and fast low intensity ultraviolet light detection, potential fluorescence based UV probing and inkless and erasable printing.

A multiple hydrogen-bonded three-dimensional supramolecular architecture composed of a unique three-fold interlocked anionic Zn(ii)-coordination architecture

A multiple hydrogen bonded 3D supramolecular architecture composed of interlocked anionic Zn(ii)-coordination architecture possesses two kinds of distinct cavities in the interlocked positions and between adjacent self-knitting layers respectively.

Polyoxometalate-based room-temperature phosphorescent materials induced by anion–π interactions

A series of polyoxometalate-based host–guest materials emit strong red room-temperature phosphorescence attributed to intermolecular charge-transfer states which was caused by unorthodox anion–π interactions.

A heterometallic D–A hybrid heterostructural framework with enhanced visible-light photocatalytic properties

A heterometallic D–A hybrid heterostructural framework from the ternary combination of CuI, lanthanide cations and viologen tectons exhibited enhanced photocatalytic activities for degradation of organic dyes.

Sun, UV and X-ray triple photochromic properties of three coordination polymers based on 1,1′-bis(3-carboxylatobenzyl)-4,4′-bipyridinium ligand

Reversible color changes for three compounds can be observed in the air upon sunlight, UV-light and X-ray irradiation.

Structural characterization and photochromic behaviour of a novel compound based on a π-acidic naphthalene diimide derivative and a double hydroxide-bridged dinuclear AlIII aqua ion cluster

Noncovalent interactions, such as π-π stacking interactions, C-H...π interactions and hydrogen bonding, are important driving forces for self-assembly in the construction of functional supermolecules and materials, especially in multicomponent supramolecular systems. Herein, a novel compound based on a π-acidic naphthalene diimide derivative and a double hydroxide-bridged dinuclear Al³⁺ aqua ion cluster, namely bis[N,N'-bis(2-sulfonatoethyl)-1,4,5,8-naphthalene diimide] di-μ-hydroxido-bis[tetraaquaaluminium(III)] tetrahydrate, (C₁₈H₁₂N₂O₁₀S₂)₂[Al₂(OH)₂(H₂O)₈]·4H₂O, was obtained using the above-mentioned common noncovalent interactions, as well as uncommon lone-pair-π interactions. Functional molecular modules were connected by these noncovalent interactions to generate obvious photochromic properties. The compound was prepared by the self-assembly of N,N'-bis(2-sulfoethyl)-1,4,5,8-naphthalene diimide and Al(NO₃)₃·9H₂O under mixed solvothermal conditions, and was characterized in detail by single-crystal X-ray diffraction, powder X-ray diffraction and FT-IR spectroscopy. The thermal stability and photochromic properties were also investigated; furthermore, in-situ solid-state UV-Vis absorption spectroscopy and electron spin resonance (ESR) were used to clarify the photochromic mechanism.

An inorganic–organic hybrid supramolecular framework based on the γ-[Mo8O26]4− cluster and cobalt complex of aspartic acid: X-ray structure and DFT study

A new inorganic–organic hybrid based on an aspartate functionalized polyoxomolybdate, [pentaaquacobalt(II)]-μ-aspartate-[γ-octamolybdate]-μ-aspartate-[pentaaquacobalt(II)] tetrahydrate, [Co2(C4H6NO4)2(γ-Mo8O26)(H2O)10]·4H2O (1), has been synthesized under hydrothermal conditions from the reaction of an Evans–Showell-type polyoxometalate, (NH4)6[Co2Mo10H4O38], and L-aspartic acid. The complex exhibits a supramolecular three-dimensional framework structure in the crystal lattice. Compound 1 was structurally characterized by elemental analyses, IR and UV–Vis (diffuse reflectance) spectroscopy and single-crystal X-ray diffraction. In this compound, aspartic acid acts as a bridge between the two Co atoms and the Mo centres, with the –CH2COOH side chain directly linked to the Mo centre in γ-[Mo8O26]4− and the α-carboxylate side chain bound to the Co centre. Commonly, the binding of transition-metal complexes to POMs involves coordination of the metal to a terminal O atom of the POM so that 1, with a bridging ligand between Mo and Co atoms, belongs to a separate class of hybrid materials. While the starting materials are both chiral and one might expect them to form a chiral hybrid, the decomposition of the chiral Evans–Showell-type POM and its conversion to the centrosymmetric γ-octamolybdate POM, plus the presence of two aspartate ligands centrosymmetrically placed on either side of the POM, leads to the formation of an achiral hybrid. We have studied energetically by means of density functional theory (DFT) calculations and using the Bader's `atoms-in-molecules' analysis the electrostatically enhanced hydrogen bonds (EEHBs) observed in the solid state of 1, which are crucial for the formation of one-dimensional supramolecular assemblies.

Bifunctional photo- and vapochromic behaviors of a novel porous zwitterionic metal–organic framework

A novel porous zwitterionic metal–organic framework shows photo- and vapochromic behaviors with high sensitivity for sensing NH₃, ethylamine, and n-propylamine.