Thermoplastic Membranes Incorporating Semiconductive Metal–Organic Frameworks: An Advance on Flexible X-ray Detectors

Semiconductive metal–organic frameworks (MOFs) have emerged in applications such as chemical sensors, electrocatalysts, energy storage materials, and electronic devices. However, examples of semiconductive MOFs within flexible electronics have not been reported. We present flexible X-ray detectors prepared by thermoplastic dispersal of a semiconductive MOF ( SCU-13 ) through a commercially available polymer, poly(vinylidene fluoride). The flexible detectors exhibit efficient X-ray-to-electric current conversion with enhanced charge-carrier mobility and low trap density compared to pelleted devices. A high X-ray detection sensitivity of 65.86 μCGy_air⁻¹ cm⁻² was achieved, which outperforms other pelleted devices and commercial flexible X-ray detectors. We demonstrate that the MOF-based flexible detectors can be operated at multiple bending angles without a deterioration in detection performance. As a proof-of-concept, an X-ray phase contrast under bending conditions was constructed using a 5×5 pixelated MOF-based imager.     

High-Performance and Self-Powered X-Ray Detectors Made of Smooth Perovskite Microcrystalline Films with 100 μm Grains

Perovskite single crystals and polycrystalline films have complementary merits and deficiencies in X-ray detection and imaging. Herein, we report preparation of dense and smooth perovskite microcrystalline films with both merits of single crystals and polycrystalline films through polycrystal-induced growth and hot-pressing treatment (HPT). Utilizing polycrystalline films as seeds, multi-inch-sized microcrystalline films can be in situ grown on diverse substrates with maximum grain size reaching 100 μm, which endows the microcrystalline films with comparable carrier mobility-lifetime (μτ) product as single crystals. As a result, self-powered X-ray detectors with impressive sensitivity of 6.1×10⁴ μC Gy_air⁻¹ cm⁻² and low detection limit of 1.5 nGy_air s⁻¹ are achieved, leading to high-contrast X-ray imaging at an ultra-low dose rate of 67 nGy_air s⁻¹. Combining with the fast response speed (186 μs), this work may contribute to the development of perovskite-based low-dose X-ray imaging.     

Dimensional and Optoelectronic Tuning of Lead-free Perovskite Cs3Bi2I9−nBrn Single Crystals for Enhanced Hard X-ray Detection

Inorganic Bi-based perovskites have shown great potential in X-ray detection for their large absorption to X-rays, diverse low-dimensional structures, and eco-friendliness without toxic metals. However, they suffer from poor carrier transport properties compared to Pb-based perovskites. Here, we propose a mixed-halogen strategy to tune the structural dimensions and optoelectronic properties of Cs₃Bi₂I_9−nBr_n (0≤n≤9). Ten centimeter-sized single crystals are successfully grown by the Bridgman technique. Upon doping bromine to zero-dimensional Cs₃Bi₂I₉, the crystal transforms into a two-dimensional structure as the bromine content reaches Cs₃Bi₂I₈Br. Correspondingly, the optoelectronic properties are adjusted. Among these crystals, Cs₃Bi₂I₈Br exhibits negligible ion migration, moderate resistivity, and the best carrier transport capability. The sensitivities in 100 keV hard X-ray detection are 1.33×10⁴ and 1.74×10⁴ μC Gy_air⁻¹ cm⁻² at room temperature and 75 °C, respectively, which are the highest among all reported bismuth perovskites. Moreover, the lowest detection limit of 28.6 nGy_air s⁻¹ and ultralow dark current drift of 9.12×10⁻⁹ nA cm⁻¹ s⁻¹ V⁻¹ are obtained owing to the high ionic activation energy. Our work demonstrates that Br incorporation is an effective strategy to enhance the X-ray detection performance by tuning the dimensional and optoelectronic properties.     

Low Bandgap 2D Perovskite Single Crystal with Anomalous-large Charges/ions Collection Ratio for Ultra-sensitive and Stable X-ray Detectors

The low-dimensional halide perovskites have attracted increasing attention due to their improved moisture stability, reduced defects, and suppressed ions migration in many optoelectronic devices such as solar cells, light-emitting diodes, X-ray detectors, and so on. However, they are still limited by their large band gap and short charge carriers’ diffusion length. Here, we demonstrate that the introduction of metal ions into organic interlayers of two-dimensional (2D) perovskite by cross-linking the copper paddle-wheel cluster-based lead bromide ([Cu(O₂C−(CH₂)₃−NH₃)₂]PbBr₄) perovskite single crystals with coordination bonds can not only significantly reduce the perovskite band gap to 0.96 eV to boost the X-ray induced charge carriers, but can also selectively improve the charge carriers’ transport along the out-of-plane direction and blocking the ions motion paths. The [Cu(O₂C−(CH₂)₃−NH₃)₂]PbBr₄ single-crystal device can reach a record charges/ions collection ratio of 1.69×10¹⁸±4.7 % μGy_air⁻¹ s, and exhibit a large sensitivity of 1.14×10⁵±7% μC Gy_air⁻¹ cm⁻² with the lowest detectable dose rate of 56 nGy_air s⁻¹ under 120 keV X-rays irradiation. In addition, [Cu(O₂C−(CH₂)₃−NH₃)₂]PbBr₄ single-crystal detector exposed to the air without any encapsulation shows excellent X-ray imaging capability with long-term operational stability without any attenuation of 120 days.     

Centimeter-Sized Single Crystal of Two-Dimensional Halide Perovskites Incorporating Straight-Chain Symmetric Diammonium Ion for X-Ray Detection

Two-dimensional (2D) AA′_n−1M_nX_3n+1 type halide perovskites incorporating straight-chain symmetric diammonium cations define a new type of structure, but their optoelectronic properties are largely unexplored. Reported here is the synthesis of a centimeter-sized AA′_n−1M_nX_3n+1 type perovskite, BDAPbI₄ (BDA=NH₃C₄H₈NH₃), single crystal and its charge-transport properties under X-ray excitation. The crystal shows a staggered configuration of the [PbI₆]⁴⁻ layers, a band gap of 2.37 eV, and a low trap density of 3.1×10⁹ cm⁻³. The single-crystal X-ray detector exhibits an excellent sensitivity of 242 μC Gy_air⁻¹ cm⁻² under the 10 V bias (0.31 V μm⁻¹), a detection limit as low as 430 nGy_air s⁻¹, ultrastable response current, a stable baseline with the lowest dark current drift of 6.06×10⁻⁹ nA cm⁻¹ s⁻¹ V⁻¹, and rapid response time of τ_rise=7.3 ms and τ_fall=22.5 ms. These crystals are promising candidates for the next generation of optoelectronic devices.     

2,3‐Dihydro‐1,3‐benzothiazol‐2‐iminium hydrogen oxydiacetate: a combined structural and theoretical study

In the title compound, C₇H₇N₂S⁺·C₄H₅O₅⁻, the ions are connected by N—H...O hydrogen bonds. The hydrogen oxydiacetate residues are linked together by O—H...O hydrogen bonds disordered about centres of inversion into hydrogen‐bonded ribbon layers crosslinked by weak C—H...O and stacking interactions. The cation exists mainly in the 2,3‐dihydro‐1,3‐benzothiazol‐2‐iminium form, with a small participation of the 2‐aminobenzothiazolium form, based on the structural data and quantum mechanical calculations. This study provides structural insights relevant to the biochemical activity of benzothiazole molecules.     

Dirubidium hexaaquacobalt(II) tetrakis(hydrogen phthalate) tetrahydrate and coordination modes of the hydrogen phthalate anion

The title compound, Rb₂[Co(H₂O)₆](C₈H₅O₄)₄·4H₂O, consists of nearly regular octahedral [Co(H₂O)₆]²⁺ cations with the Co^II cations on the inversion centre (special position 2a), Rb⁺ cations, hydrogen phthalate (Hpht⁻) anions and disordered water molecules. The Rb⁺ cation is surrounded by nine O atoms from Hpht⁻ anions and water molecules, with a strongly deformed pentagonal–bipyramidal geometry and one apex split into three positions. The crystal packing is governed by numerous hydrogen bonds involving all water molecules and Hpht⁻ anions. In this way, layers parallel to the ab plane are formed, with the aromatic rings of the Hpht⁻ anions esentially directed along the c axis. While Hpht⁻ anions form the outer part of the layers, disordered water molecules and Rb⁺ cations alternate with [Co(H₂O)₆]²⁺ cations in the inner parts. The only interactions between the layers are van der Waals forces between the atoms of the aromatic rings. A search of the Cambridge Structural Database for coordination modes and types of hydrogen‐bonding interaction of the Hpht⁻ anion showed that, when uncoordinated Hpht⁻ anions are present, compounds with intermolecular hydrogen bonds are more numerous than compounds with intramolecular hydrogen bonds. For coordinated Hpht⁻ anions, chelating and bridging anions are almost equally common, while monodentate anions are relatively scarce. The same coordination modes appear for Hpht⁻ anions with or without intramolecular hydrogen bonds, although intramolecular hydrogen bonds are less common.     

N—H...O and O—H...O hydrogen‐bonded supramolecular networks in 4‐chloroanilinium, 2‐hydroxyanilinium and 3‐hydroxyanilinium hydrogen phthalates

The title salts, 4‐chloroanilinium hydrogen phthalate (PCAHP), C₆H₇ClN⁺·C₈H₅O₄⁻, 2‐hydroxyanilinium hydrogen phthalate (2HAHP), C₆H₈NO⁺·C₈H₅O₄⁻, and 3‐hydroxyanilinium hydrogen phthalate (3HAHP), C₆H₈NO⁺·C₈H₅O₄⁻, all crystallize in the space group P2₁/c. The asymmetric unit of 2HAHP contains two independent ion pairs. The hydrogen phthalate ions of 2HAHP and 3HAHP show a short intramolecular O—H...O hydrogen bond, with O...O distances ranging from 2.3832 (15) to 2.3860 (14) Å. N—H...O and O—H...O hydrogen bonds, together with short C—H...O contacts in PCAHP and 3HAHP, generate extended hydrogen‐bond networks. PCAHP forms a two‐dimensional supramolecular sheet extending in the (100) plane, whereas 2HAHP has a supramolecular chain running parallel to the [100] direction and 3HAHP has a two‐dimensional network extending parallel to the (001) plane.     

Coordination-Induced N−H Bond Splitting of Ammonia and Primary Amine of CuI−MOFs

We report a porous three-dimensional anionic tetrazolium based Cu^I−MOF 1 , which is capable of cleaving the N−H bond of ammonia and primary amine, as well as the O−H bond of H₂O along with spontaneous H₂ evolution. In the gas-solid phase reaction of 1 with ammonia and water vapor, Cu^I−MOF 1 was gradually oxidized to NH₂−Cu^II−MOF and OH−Cu^II−MOF, through single-crystal-to-single-crystal (SCSC) structural transformations, which was confirmed by XPS, PXRD and X-ray single-crystal diffraction. Density functional theory (DFT) demonstrated that Cu^I−MOF could lower N−H bond dissociation free energy of ammonia through coordination-induced bond weakening and promote H₂ evolution by the reduction potential of 1 . To our knowledge, this is the first example of MOFs that activate ammonia and amine in gas-solid manner.     

CO2 Laser-Induced Graphene with an Appropriate Oxygen Species as an Efficient Electrocatalyst for Hydrogen Peroxide Synthesis

Oxygen species functionalized graphene (O−G) is an effective electrocatalyst for electrochemically synthesizing hydrogen peroxide (H₂O₂) by a 2 e⁻ oxygen reduction reaction (ORR). The type of oxygen species and degree of carbon crystallinity in O−G are two key factors for the high catalytic performance of the 2 e⁻ ORR. However, the general preparing method of O−G by the precursor of graphite has the disadvantages of consuming massive strong oxidant and washing water. Herein, the biomass-based graphene with tunable oxygen species is rapidly fabricated by a CO₂ laser. In a flow cell setup, the laser-induced graphene (LIG) with abundant active oxygen species and graphene structure shows high catalytic performance including high Faraday efficiency (over 78 %) and high mass activity (814 mmolg_catalyst⁻¹ h⁻¹), superior to most of the reported carbon-based electrocatalysts. Density function theory demonstrates the meta-C atoms at nearby C−O, O−C=O species are the key catalytic sites. Therefore, we develop one facile method to rapidly convert biomass to graphene electrocatalyst used for H₂O₂ synthesis.     

Isomorphous crystals of strychninium 4‐chloro­benzoate and strychninium 4‐nitro­benzoate

In strychninium 4‐chloro­benzoate, C₂₁H₂₃N₂O₂⁺·C₇H₄ClO₂⁻, (I), and strychninium 4‐nitro­benzoate, C₂₁H₂₃N₂O₂⁺·C₇H₄NO₄⁻, (II), the strychninium cations form pillars stabilized by C—H⋯O and C—H⋯π hydrogen bonds. Channels between the pillars are occupied by anions linked to one another by C—H⋯π hydrogen bonds. The cations and anions are linked by ionic N—H⁺⋯O⁻ and C—H⋯X hydrogen bonds, where X = O, π and Cl in (I), and O and π in (II).     

A long Nb=O double bond in bis(pyridinium) tetra­chlorooxo(pyridine‐κN)niobate(V) chloride

The asymmetric unit of the title compound, (C₅H₆N)₂[NbCl₄O(C₅H₅N)]Cl or (pyH)₂[O=NbCl₄(py)]Cl (py is pyridine), contains a discrete anionic niobium(V) complex, [O=NbCl₄(py)]⁻, and two protonated pyridine mol­ecules, which form medium–strong hydrogen bonds with the Cl⁻ counter‐ion. The Nb=O distance of 1.7643 (17) Å is the longest among those in congener niobium complexes reported to date. Extensive density functional theory studies of conformations of [O=NbCl₄(py)]⁻ and structural data mining raise doubts regarding the reliability of the length of this Nb=O double bond.     

2,2′‐Bipyridinium(1+) bromide monohydrate

In the crystal structure of 2,2′‐bipyridinium(1+) bromide monohydrate, C₁₀H₉N₂⁺·Br⁻·H₂O, the cation has a cisoid conformation with an intramolecular N—H⋯N hydrogen bond. The cation also forms an N—H⋯O hydrogen bond to an adjacent water mol­ecule, which in turn forms O—H⋯Br⁻ hydrogen bonds to adjacent Br⁻ anions. In this way, a chain is formed extending along the b axis. Additional interactions (C—H⋯Br⁻ and π–π) serve to stabilize the structure further.     

A dihydrogen phosphate anionic network as a host lattice for cations in 1‐methylpiperazine‐1,4‐diium bis(dihydrogen phosphate) and 2‐(pyridin‐2‐yl)pyridinium dihydrogen phosphate–orthophosphoric acid (1/1)

In the salt 1‐methylpiperazine‐1,4‐diium bis(dihydrogen phosphate), C₅H₁₃N₂²⁺·2H₂PO₄⁻, (I), and the solvated salt 2‐(pyridin‐2‐yl)pyridinium dihydrogen phosphate–orthophosphoric acid (1/1), C₁₀H₉N₂⁺·H₂PO₄⁻·H₃PO₄, (II), the formation of O—H...O and N—H...O hydrogen bonds between the dihydrogen phosphate (H₂PO₄⁻) anions and the cations constructs a three‐ and two‐dimensional anionic–cationic network, respectively. In (I), the self‐assembly of H₂PO₄⁻ anions forms a two‐dimensional pseudo‐honeycomb‐like supramolecular architecture along the (010) plane. 1‐Methylpiperazine‐1,4‐diium cations are trapped between the (010) anionic layers through three N—H...O hydrogen bonds. In solvated salt (II), the self‐assembly of H₂PO₄⁻ anions forms a two‐dimensional supramolecular architecture with open channels projecting along the [001] direction. The 2‐(pyridin‐2‐yl)pyridinium cations are trapped between the open channels by N—H...O and C—H...O hydrogen bonds. From a study of previously reported structures, dihydrogen phosphate anions show a supramolecular flexibility depending on the nature of the cations. The dihydrogen phosphate anion may be suitable for the design of the host lattice for host–guest supramolecular systems.     

Unprecedented Chiral Three-dimensional Hybrid Organic-Inorganic Perovskitoids

Chiral three-dimensional hybrid organic–inorganic perovskites (3D HOIPs) would show unique chiroptoelectronic performance due to the combination of chirality and 3D structure. However, the synthesis of 3D chiral HOIPs remains a significant challenge. Herein, we constructed a pair of unprecedented 3D chiral halide perovskitoids (R/S-BPEA)EA₆Pb₄Cl₁₅ ( 1-R/S ) (R/S-BPEA=(R/S)-1-4-Bromophenylethylammonium, EA=ethylammonium), in which the large chiral cations can be contained in the big “hollow” inorganic frameworks induced by mixing cations. Notably, 3D 1-R/S shows natural chiroptical activity, as evidenced by its significant mirror circular dichroism spectra and the ability to distinguish circularly polarized light. Moreover, based on the unique 3D structure, 1-S presents sensitive X-ray detection performance with a low detection limit of 398 nGy_air s⁻¹, which is 14 times lower than the regular medical diagnosis of 5.5 μGy_air s⁻¹. In this work, 3D chiral halide perovskitoids provide a new route to develop chiral material in spintronics and optoelectronics.     

Anilinium dihydrogen phosphate

The triclinic structure of the title compound, C₆H₈N⁺·H₂PO₄⁻, with three symmetry‐independent structural units (Z′ = 3), is formed of separate organic and inorganic layers alternating along the b axis. The building blocks of the inorganic layer are deformed H₂PO₄ tetrahedra assembled into infinite ladders by short and hence strong hydrogen bonds. The anilinium cations forming the organic layer are not hydrogen bonded to one another, but they are anchored by four N—H...O crosslinks between the dihydrogen phosphate chains of adjacent ladders. Two H atoms of each –NH₃ group then form one normal and one bifurcated N—H...O hydrogen bond to the P=O oxygens of two tetrahedra of one chain, while the third H atom is hydrogen bonded to the nearest O atom of an adjacent chain belonging to another dihydrogen phosphate ladder.     

Antisolvent-assisted Crystallization of Centimeter-sized Lead-free Bismuth Bromide Hybrid Perovskite Single Crystals with X-ray Sensitive Merits

Hybrid bismuth halides perovskites have emerged as promising candidates for X-ray detection, due to the strong absorptivity of high-energy X-ray photons, high resistivity, large carrier diffusion length and low toxicity. However, the mostly investigated hybrid bismuth iodides single crystals are usually opaque and require a harsh synthesis process. Herein, novel one-dimensional (1D) pentamethylenediamine bismuth bromide (PDA)BiBr₅ single crystals were synthesized via an antisolvent-assisted crystallization method at room temperature. Bulk (PDA)BiBr₅ single crystals have sizes of 10×1.3×1.5 mm³ and high transparency. They are shown to have low density of defects of 2.0×10¹⁰ cm⁻³ and obvious photoconductivity. Moreover, they exhibit large bulk resistivity of 2.13×10¹¹ Ω cm and good X-ray attenuation coefficient. Consequently, the vertical structured (PDA)BiBr₅ single crystal X-ray photoconductor produces a sensitivity of 3.8 μC Gy_air⁻¹ cm⁻². This study provides a facile strategy for synthesizing bulk hybrid bismuth bromides single crystals with potential X-ray detection application.     

Simultaneous Sensing of H2O,D2O and HOD through Peroxo Vibrations

Detection of HOD simultaneously in the presence of a mixture of H₂O and D₂O is still an experimental challenge. Till date, there is no literature report of simultaneous detection of H₂O, D₂O and HOD based on vibrational spectra. Herein we report simultaneous quantitative detection of H₂O, D₂O and HOD in the same reaction mixture with the help of bridged polynuclear peroxo complex in absence and presence of Au nanoparticles on the basis of a peroxide vibrational mode in resonance Raman and surface enhanced resonance Raman spectrum. We synthesize bridged polynuclear peroxo complex in different solvent mixture of H₂O and D₂O. Due to the formation of different nature of hydrogen bonding between peroxide and solvent molecules (H₂O, D₂O and HOD), vibrational frequency of peroxo bond is significantly affected. Mixtures of different H₂O and D₂O concentrations produce different HOD concentrations and that lead to different intensities of peaks positioned at 897, 823 and 867 cm⁻¹ indicating H₂O, D₂O and HOD, respectively. The lowest detection limits (LODs) were 0.028 mole fraction of D₂O in H₂O and 0.046 mole faction of H₂O in D₂O. In addition, for the first time the results revealed that the cis-peroxide forms two hydrogen bonds with solvent molecules.     

Two Three‐Dimensional Metal‐Organic Frameworks Constructed from Alkaline Earth Metal Cations (Sr and Ba) and 5‐Nitroisophthalicacid – Synthesis,Charaterization, and Thermochemistry

Two MOFs of [Sr^II(5‐NO₂‐BDC)(H₂O)₆] ( 1 ) and [Ba^II(5‐NO₂‐BDC)(H₂O)₆] ( 2 ) have been synthesized in water using alkaline earth metal salts and the rigid organic ligand 5‐NO₂‐H₂BDC. The compounds were characterized by elemental analysis, infrared spectrum, thermal analysis, and X‐ray crystallography. Crystal structure analyses have shown that the two complexes are isostructural as evidenced by IR spectra and TG‐DTA. Both compounds present three‐dimensional frameworks built up from infinite chains of edge‐sharing twelve‐membered rings through O–H···O hydrogen bonds. The specific heat capacities of the title complexes have been determined by an improved RD496‐III microcalorimeter with the values of (109.29 ± 0.693) J mol⁻¹ K⁻¹ and (81.162 ± 0.858) J mol⁻¹ K⁻¹ at 298.15 K, and the molar enthalpy changes of the formation reactions of complexes at 298.15 K were calculated as (4.897 ± 0.008) kJ mol⁻¹ and (2.617 ± 0.009) kJ mol⁻¹, respectively.     

Emergence of a Lanthanide Chalcogenide as an Ideal Scintillator for a Flexible X-ray Detector

The development of high-performance X-ray detectors requires scintillators with fast decay time, high light yield, stability, and X-ray absorption capacity, which are difficult to achieve in a single material. Here, we present the first example of a lanthanide chalcogenide of LaCsSiS₄ : 1 % Ce³⁺ that simultaneously integrates multiple desirable properties for an ideal scintillator. LaCsSiS₄ : 1 % Ce³⁺ demonstrates a remarkably low detection limit of 43.13 nGy_air s⁻¹ and a high photoluminescence quantum yield of 98.24 %, resulting in a high light yield of 50480±1441 photons/MeV. Notably, LaCsSiS₄ : 1 % Ce³⁺ exhibits a fast decay time of only 29.35±0.16 ns, making it one of the fastest scintillators among all lanthanide-based inorganic scintillators. Furthermore, this material shows robust radiation and moisture resistance, endowing it with suitability for chemical processing under solution conditions. To demonstrate the X-ray imaging capacity of LaCsSiS₄ : 1 % Ce³⁺, we fabricated a flexible X-ray detector that achieved a high spatial resolution of 8.2 lp mm⁻¹. This work highlights the potential of lanthanide chalcogenide as a promising candidate for high-performance scintillators.