Host Framework Research Articles

A Low‐Cost Facile Synthesis of Solution‐Processable N‐Phenylcarbazole/Triazine Hybrid Host for Orange Thermally‐Activated Delayed Fluorescent Organic Light‐Emitting Diodes

An N‐phenylcarbazole/triazine hybrid of 2,4,6‐tris(9‐phenyl‐9H‐carbazol‐3‐yl)‐1,3,5‐triazine (TPhCz‐Trz) is successfully synthesized using cheap raw materials via facile synthesis method with a high yield of 60.9%. Good thermal (Td, 284 °C) and morphological stability are realized due to its rigid structure and three‐dimensional steric hindrance. The high triplet energy level of 2.88 eV for the host is very important to inhibit the energy reverse from guest to host. Surprisingly, orange thermally‐activated delayed fluorescent (TADF) organic light‐emitting diodes (OLEDs) are achieved by using excellent green emitter 9,10‐bis(4‐(3,6‐ditertbutyl‐9H‐carbazol‐9‐yl)‐2,6‐dimethyl‐phenyl)‐9,10‐diboraanth‐racene (tBuCzDBA) with the maximum external quantum efficiency of 14.0%. The large bathochromic‐shift is probably induced by the polarity of the host compared to the emission peak of 542 nm of tBuCzDBA‐based green TADF device. This indicates high performance of devices with different colors would be achieved through optimizing molecular structure of the host and device framework using tBuCzDBA as emitter.

Hydrogen-bonded frameworks for conformational analysis of reactive substrates.

Guanidinium organosulfonate (GS) hydrogen-bonded host frameworks were used to trap α-halopropiophenones and α-halocyclooctanones to determine their molecular structure by single crystal X-ray diffraction. The majority of encapsulated guest molecules adopted conformations expected from computational analysis and stereochemical outcomes of Grignard reactions.

Investigating the mechanism of phosphorene nanoribbon synthesis by discharging black phosphorus intercalation compounds.

Phosphorene nanoribbons (PNRs) can be synthesised in intrinsically scalable methods from intercalation of black phosphorus (BP), however, the mechanism of ribbonisation remains unclear. Herein, to investigate the point at which nanoribbons form, we decouple the two key synthesis steps: first, the formation of the BP intercalation compound, and second, the dissolution into a polar aprotic solvent. We find that both the lithium intercalant and the negative charge on the phosphorus host framework can be effectively removed by addition of phenyl cyanide to return BP and investigate whether fracturing to ribbons occurred after the first step. Further efforts to exfoliate mechanically with or without solvent reveal that the intercalation step does not form ribbons, indicating that an interaction between the amidic solvent and the intercalated phosphorus compound plays an important role in the formation of nanoribbons.

Ion-Molecule Co-Confining Ammonium Vanadate Cathode for High-Performance Aqueous Zinc-Ion Batteries.

Vanadium-based cathode materials have attracted great attention in aqueous zinc-ion batteries (AZIBs). However, the inferior ion transport and cyclic stability due to the strong Coulomb interaction between Zn2+ and the lattice limit their further application. In this work, CO2 molecules are in situ embedded in the interlayer structure of NH4V4O10 by decomposing excess H2C2O4·2H2O in the main framework, obtaining an ion-molecule co-confining NH4V4O10 for AZIB cathode material. The introduced CO2 molecules expanded the interlayer spacing of NH4V4O10, broadened the diffusion channel of Zn2+, and stabilized the structure of NH4V4O10 as the interlayer pillars together with , which effectively improved the Zn2+ diffusion kinetics and cycle stability of the electrode. In addition, the binding between and the host framework is stabilized via hydrogen bonds with CO2 molecules. NVO-CO2-0.8 exhibited excellent specific capacity (451.1mAhg-1 at 2 Ag-1), cycle stability (214.0mAhg-1 at 10Ag-1 after 1000 cycles) and rate performance. This work provides new ideas and approaches for optimizing vanadium-based materials with high-performance AZIBs.

Ion-pairing design of covalent organic framework membranes for separation and controlled release of pharmaceuticals

Intrinsically charged covalent organic frameworks (COFs) afford specific ionic nanochannels for mass transport, and thus become promising platforms to design membranes with unique selectivity. However, internal electrostatic repulsion and large-pore frameworks cause significant barriers that greatly limit membrane performances. Herein, we report a novel strategy to synchronously crystallize and upgrade cationic COF membranes by ion-pairing design. Ion-paired guest molecules are involved in electric-driven interfacial crystallization to offset the charges of the ionic monomers and host frameworks. This host-guest neutralization promotes the crystallization of compact COF membranes. Lateral dimension and charge nature of guest molecules fundamentally affect the ion-pairing efficiency. Tight encapsulation of the large-sized electronegative molecules effectually narrows the molecular sieving channels, yielding a significant elevation in membrane selectivity. The membrane rejection of organic ions with a size larger than 1.2 nm thus can be improved from below 50 % to above 85 % with a water permeance of ∼10 L m−2 h−1 bar−1. Prominently, our membranes demonstrate efficient recovery and pH-dependent release of bioactive pharmaceuticals, with a release rate that is 12 times higher in an acidic solution compared to a neutral environment. This work provides an ion-pairing strategy to regulate COF membranes for pharmaceutical industries and beyond.

Viologen Guest-Mediated Luminescence Emission Tuning and Photochromic Behavior by a Series of Viologen@Zn-MOF Materials.

The encapsulation of various guest molecules into the pores of metal-organic frameworks (MOFs) to form hybrid materials has attracted significant attention due to their unique spatial distribution and certain preferential geometry of the guests inside the MOFs. This arrangement often results in the guests exhibiting unique physical and chemical properties due to their intramolecular interactions with the host. In this article, five viologen derivatives were introduced as guests in a Zn-MOF with different benzene ring lengths, resulting in the formation of host-guest three-dimensional (3D) MOFs. The five compounds exhibited guest-dependent emission wavelength, color, and excellent photochromic behavior upon ultraviolet (UV) light radiation due to the distinct electronic transfer and π···π stacking interactions between the viologen guests and the host framework. This study provides a host-guest strategy for designing color-tunable luminescent and highly sensitive photochromic materials.

Dynamic Lone Pairs and Fluoride-Ion Disorder in Cubic-BaSnF4.

Introducing compositional or structural disorder within crystalline solid electrolytes is a common strategy for increasing their ionic conductivity. (M,Sn)F2 fluorites have previously been proposed to exhibit two forms of disorder within their cationic host frameworks: occupational disorder from randomly distributed M and Sn cations and orientational disorder from Sn(II) stereoactive lone pairs. Here, we characterize the structure and fluoride-ion dynamics of cubic BaSnF4, using a combination of experimental and computational techniques. Rietveld refinement of the X-ray diffraction (XRD) data confirms an average fluorite structure with {Ba,Sn} cation disorder, and the 119Sn Mössbauer spectrum demonstrates the presence of stereoactive Sn(II) lone pairs. X-ray total-scattering PDF analysis and ab initio molecular dynamics simulations reveal a complex local structure with a high degree of intrinsic fluoride-ion disorder, where 1/3 of fluoride ions occupy octahedral "interstitial" sites: this fluoride-ion disorder is a consequence of repulsion between Sn lone pairs and fluoride ions that destabilizes Sn-coordinated tetrahedral fluoride-ion sites. Variable-temperature 19F NMR experiments and analysis of our molecular dynamics simulations reveal highly inhomogeneous fluoride-ion dynamics, with fluoride ions in Sn-rich local environments significantly more mobile than those in Ba-rich environments. Our simulations also reveal dynamical reorientation of the Sn lone pairs that is biased by the local cation configuration and coupled to the local fluoride-ion dynamics. We end by discussing the effect of host-framework disorder on long-range diffusion pathways in cubic BaSnF4.

Electrochemically activated Mn3O4 nanoparticles as higher performing electrode than MnO2 for Al-ion batteries – An insight into the crystallographic changes caused by Al3+ intercalation

Aluminium is the third most abundant element in the earth's crust, with a high theoretical capacity and volumetric energy density, making aluminium ion batteries (AIBs) a preferred technology for future large-scale energy storage applications amongst all of the proposed nonlithium-based battery systems. However, the practical realization of AIBs has so far been impeded by the frequent collapse of the host framework of the cathode materials. Here, nanostructure of Mn3O4 is being reported as a cathode material for aqueous AIBs to enhance the specific capacity, rate capability, and cycling stability. The various salts of aluminium were used as an electrolyte to verify how the composition of the electrolyte affected the intercalation and deintercalation of Al3+ in Mn3O4 electrode. In AlCl3 aqueous electrolyte, the Mn3O4 cathode exhibits the highest initial discharge capacity of ∼ 271 mAh g−1, at a high current density of 0.5 A g−1, with an excellent capacity retention of 98 % after 1,000 cycles. The outstanding cycling stability of the synthesized Mn3O4 nanoparticles is established by considering the phase transition from Mn3O4 spinel to MnO2 layered structure. The intercalation/deintercalation of Al3+ into/from the Mn3O4 crystal structure is also being confirmed by analysing the electrochemical performance in NaCl, KCl, and H2SO4 electrolyte.

Strategy for a Rational Design of Deep-Ultraviolet Nonlinear Optical Materials from Zeolites.

Deep-ultraviolet (DUV) nonlinear optical (NLO) materials play a crucial role in cutting-edge laser technology. In order to solve the serious layered growth tendency of the sole commercial DUV NLO crystal KBe2BO3F2 (KBBF), developing alternative systems of compounds with bulk crystal habits has become an urgent task for practical applications. Herein, a novel strategy was developed by applying non-centrosymmetric (NCS) cancrinite (CAN)-type zincophosphates {Na6(OH)2(H2O)2}Cs2[ZnPO4]6 with bulk-crystal habits as the prototype to design new DUV NLO crystals. Two new anhydrous alkali zincophosphates, namely, {(Li6-xNaxO)A2}[(ZnPO4)6] (A = Cs, Rb; x = 2-3) crystallizing in the NCS hexagonal space group P63 (no. 173) with a CAN-type framework, were successfully synthesized via a modified fluoro-solvo-hydrothermal method by applying triethylamine (TEA) and concentrated NaF solution as a co-solvent. Interestingly, the rigidity of the NCS CAN-type framework acting as the host ensures the non-centrosymmetry of the resulting new compounds. Meanwhile, the replacement of water molecules by guest cationic species in the channels or cages can greatly improve the thermal stability of the resultant crystal and tune its NLO properties. The synergetic effect of the host framework and the guest species makes the two compounds transparent down to the DUV region (<200 nm) and exhibit SHG effects. Therefore, the proposed rational design strategy of applying the known zeotype NCS frameworks as prototypes together with the modified fluoro-solvo-hydrothermal method opens a great avenue for highly effectively exploring new DUV NLO materials.

Enhanced Bioactivity of Enzyme/MOF Biocomposite via Host Framework Engineering.

This study reports the successful development of a sustainable synthesis protocol for a phase-pure metal azolate framework (MAF-6) and its application in enzyme immobilization. An esterase@MAF-6 biocomposite was synthesized, and its catalytic performance was compared with that of esterase@ZIF-8 and esterase@ZIF-90 in transesterification reactions. Esterase@MAF-6, with its large pore aperture, showed superior enzymatic performance compared to esterase@ZIF-8 and esterase@ZIF-90 in catalyzing transesterification reactions using both n-propanol and benzyl alcohol as reactants. The hydrophobic nature of the MAF-6 platform was shown to activate the immobilized esterase into its open-lid conformation, which exhibited a 1.5- and 4-times enzymatic activity as compared to free esterase in catalyzing transesterification reaction using n-propanol and benzyl alcohol, respectively. The present work offers insights into the potential of MAF-6 as a promising matrix for enzyme immobilization and highlights the need to explore MOF matrices with expanded pore apertures to broaden their practical applications in biocatalysis.

Mapping Heterogeneity of Pristine and Aged Li- and N-Mnhcf Cathode by Synchrotron-Based Energy-Dependent Full Field Transmission X-ray Microscopy.

Manganese hexacyanoferrate is a promising cathode material for lithium and sodium ion batteries, however, it suffers of capacity fading during the cycling process. To access the structural and functional characteristics at the nanometer scale, fresh and cycled electrodes are extracted and investigated by transmission soft X-ray microscopy, which allows chemical characterization with spatial resolution from position-dependent x-ray spectra at the Mn L-, Fe L- and N K-edges. Furthermore, soft X-rays prove to show superior sensitivity toward Fe, compare to hard X-rays. Inhomogeneities within the samples are identified, increasing in the aged electrodes, more dramatically in the Li-ion system, which explains the poorer cycle life as Li-ion cathode material. Local spectra, revealing different oxidation states over the sample with strong correlation between the Fe L-edge, Mn L-edge, and N K-edge, imply a coupling between redox centers and an electron delocalization over the host framework.

Effect of CS2 and CO2 adsorption on the thermally-induced spin crossover in ferrous nitroprussides. Nature of the guest-host interactions

Tuning physical and functional properties in porous solids by introducing guest species in their framework is an attractive research area in functional materials. Such a possibility is realizable in spin-crossover (SCO) materials, where an external stimulus induces the spin transition. 2D ferrous nitroprusside pillared with organic ligands forms a novel series of porous solids with SCO behavior. This study reports the effect of CS2 and CO2 adsorption on the thermally-induced SCO in 2D ferrous nitroprusside with pyrazine, pyridine, 3-fluor pyridine, 4-methyl pyridine, and 4-pyridine carboxaldehyde as pillar molecules. The adsorption of CS2 and CO2 in the framework of these five materials produces relevant changes in the temperature values where the spin transition is observed and the kinetic effects of that process. The nature of the guest-host interactions was elucidated using IR and Mössbauer spectroscopies, XRD structural analysis of the guest-host systems, and SQUID magnetic measurements. That experimental study was complemented by computational calculations, using the VASP software package, of the most stable structure for the materials with and without the presence of the guest species in the host framework. The adsorption forces for these two guest molecules in the considered solids are related to electrostatic guest-host interactions in the interlayer region. No similar study has been reported for the effect of guest species on the SCO properties of ferrous nitroprussides.

A systematic study of the interplay between guest molecule structure and intermolecular interactions in crystalline sponges.

Utilization of the crystalline sponge {[(ZnI2)3(tpt)2·x(solvent)]n} method has enabled characterization of a novel family of synthetic organic oils. The systematic structural differences and diversity of functional groups offered by 13 related molecular adsorbates provide a detailed quantitative understanding of the relationship between the guest structure, its conformation, and the type of intermolecular interactions adopted with neighbouring guests and the host framework. This analysis is extended to assess the connection of these factors to the resulting quality indicators for a particular molecular structure elucidation.

Structure and Ionic Conductivity of Li-Disordered Bismuth o-Thiophosphate Li60-3xBi16+x(PS4)36.

The structure of the first lithium-containing bismuth ortho (o)-thiophosphate was determined using a combination of powder X-ray, neutron, and electron diffraction. Li60-3xBi16+x(PS4)36 with x in the range of 4.1-6.5 possesses a complex monoclinic structure [space group C2/c (No. 15)] and a large unit cell with the lattice parameters a = 15.4866 Å, b = 10.3232 Å, c = 33.8046 Å, and β = 85.395° for Li44.4Bi21.2(PS4)36, in agreement with the structure as observed by X-ray and neutron pair distribution function analysis. The disordered distribution of lithium ions within the interstices of the dense host structure and the Li ion dynamics and diffusion pathways have been investigated by solid-state nuclear magnetic resonance (NMR) spectroscopy, pulsed field gradient NMR diffusion measurements, and bond valence sum calculations. The total lithium ion conductivities range from 2.6 × 10-7 to 2.8 × 10-6 S cm-1 at 20 °C with activation energies between 0.29 and 0.32 eV, depending on the bismuth content. Despite the highly disordered nature of lithium ions in Li60-3xBi16+x(PS4)36, the underlying dense host framework appears to limit the dimensionality of the lithium diffusion pathways and emphasizes once more the necessity of a close inspection of the structure-property relationships in solid electrolytes.

The Impact of Environmental and Host Factors on Human Cystic Echinococcosis: A County-Level Modeling Study in Western China.

Human cystic echinococcosis (CE) is a parasitic disease caused by tapeworms from the Echinococcus granulosus genus, potentially affected by the environment and host animals. West China is one of the most endemic areas of human CE nation and worldwide. The current study identifies the crucial environmental and host factors of human CE prevalence in the Qinghai-Tibet Plateau and non-Qinghai-Tibet Plateau regions. An optimal county-level model was used to analyze the association between key factors and human CE prevalence within the Qinghai-Tibet Plateau. Geodetector analysis and multicollinearity tests identify key factors, and an optimal model is developed through generalized additive models. In the Qinghai-Tibet Plateau, four key factors were identified from the 88 variables, such as maximum annual precipitation (Pre), maximum summer normalized difference vegetation index (NDVI), Tibetan population rate (TibetanR), and positive rates of Echinococcus coproantigen in dogs (DogR). Based on the optimal model, a significant positive linear relationship was observed between maximum annual Pre and human CE prevalence. A probable U-shaped curve depicts the non-linear relationship between maximum summer NDVI and the human CE prevalence. Human CE prevalence possesses significant positive non-linear relationships with TibetanR and DogR. Human CE transmission is integrally affected by environmental and host factors. This explains the mechanism of human CE transmission based on the pathogen, host, and transmission framework. Therefore, the current study provides references and innovative ideas for preventing and controlling human CE in western China.

Extreme phonon anharmonicity underpins superionic diffusion and ultralow thermal conductivity in argyrodite Ag8SnSe6.

Ultralow thermal conductivity and fast ionic diffusion endow superionic materials with excellent performance both as thermoelectric converters and as solid-state electrolytes. Yet the correlation and interdependence between these two features remain unclear owing to a limited understanding of their complex atomic dynamics. Here we investigate ionic diffusion and lattice dynamics in argyrodite Ag8SnSe6 using synchrotron X-ray and neutron scattering techniques along with machine-learned molecular dynamics. We identify a critical interplay of the vibrational dynamics of mobile Ag and a host framework that controls the overdamping of low-energy Ag-dominated phonons into a quasi-elastic response, enabling superionicity. Concomitantly, the persistence of long-wavelength transverse acoustic phonons across the superionic transition challenges a proposed 'liquid-like thermal conduction' picture. Rather, a striking thermal broadening of low-energy phonons, starting even below 50 K, reveals extreme phonon anharmonicity and weak bonding as underlying features of the potential energy surface responsible for the ultralow thermal conductivity (<0.5 W m-1 K-1) and fast diffusion. Our results provide fundamental insights into the complex atomic dynamics in superionic materials for energy conversion and storage.

Quasi‐Topological Intercalation Mechanism of Bi0.67NbS2 Enabling 100 C Fast‐Charging for Sodium‐Ion Batteries

AbstractAlloying‐type bismuth with high volumetric capacity has emerged as a promising anode for sodium‐ion batteries but suffers from large volume expansion and continuous pulverization. Herein, a coordination constraint strategy is proposed, that is, chemically confining atomic Bi in an intercalation host framework via reconstruction‐favorable linear coordination bonds, enabling a novel quasi‐topological intercalation mechanism. Specifically, micron‐sized Bi0.67NbS2 is synthesized, in which the Bi atom is linearly coordinated with two S atoms in the interlayer of NbS2. The robust Nb−S host framework provides fast ion/electron diffusion channels and buffers the volume expansion of Na+ insertion, endowing Bi0.67NbS2 with a lower energy barrier (0.141 vs. 0.504 eV of Bi). In situ and ex situ characterizations reveal that Bi atom alloys with Na+ via a solid‐solution process and is constrained by the reconstructed Bi−S bonds after dealloying, realizing complete recovery of crystalline Bi0.67NbS2 phase to avoid the migration and aggregation of atomic Bi. Accordingly, the Bi0.67NbS2 anode delivers a reversible capacity of 325 mAh g−1 at 1 C and an extraordinary ultrahigh‐rate stability of 226 mAh g−1 at 100 C over 25 000 cycles. The proposed quasi‐topological intercalation mechanism induced by coordinated mode modulation is expected to be be conducive to the practical electrode design for fast‐charging batteries.

Chemical lithiation methodology enabled Prussian blue as a Li-rich cathode material for secondary Li-ion batteries

Prussian blue analogues (PBAs) have been attracting intense attention owing to its two-electron storage capability and considerable cost advantage, especially in Na-ion and K-ion batteries. However, things are quite different when it comes to Li-ion batteries, because lithium-containing Li4Fe(CN)6 precursor is not commercially available and thus the traditionally prepared Li-deficient FeFe(CN)6 products fail to couple with commercial graphite anode for full cells. Herein, we put forward a potential matching principle to guide the chemical pre-lithiation of FeFe(CN)6 into a Li-rich LixFeFe(CN)6 (x varies from 0 to 2) cathode. The potential matching principle was convincingly confirmed by theoretical analysis and over-lithiation experiments. Perylene-Li reagent was elaborately screened to serve as both Li+ and electron donor for controllable chemical lithiation reaction while preserving the host framework stable. Our work provided a general guiding principle and effective methodology for controllable synthesis of Prussian blue analogues in gradient lithiation depth, which could be served as a platform for in-depth, systematic and comprehensive research on the properties of PBAs materials.

Decoupling Redox Hopping and Catalysis in Metal‐Organic Frameworks ‐based Electrocatalytic CO2 Reduction

AbstractTraditional MOF e‐CRR, constructed from catalytic linkers, manifest a kinetic bottleneck during their multi‐electron activation. Decoupling catalysis and charge transport can address such issues. Here, we build two MOF/e‐CRR systems, CoPc@NU‐1000 and TPP(Co)@NU‐1000, by installing cobalt metalated phthalocyanine and tetraphenylporphyrin electrocatalysts within the redox active NU‐1000 MOF. For CoPc@NU‐1000, the e‐CRR responsive CoI/0 potential is close to that of NU‐1000 reduction compared to the TPP(Co)@NU‐1000. Efficient charge delivery, defined by a higher diffusion (Dhop=4.1×10−12 cm2 s−1) and low charge‐transport resistance ( =59.5 Ω) in CoPC@NU‐1000 led FECO=80 %. In contrast, TPP(Co)@NU‐1000 fared a poor FECO=24 % (Dhop=1.4×10−12 cm2 s−1 and =91.4 Ω). For such a decoupling strategy, careful choice of the host framework is critical in pairing up with the underlying electrochemical properties of the catalysts to facilitate the charge delivery for its activation.

Decoupling Redox Hopping and Catalysis in Metal-Organic Frameworks -based Electrocatalytic CO2 Reduction.

Traditional MOF e-CRR, constructed from catalytic linkers, manifest a kinetic bottleneck during their multi-electron activation. Decoupling catalysis and charge transport can address such issues. Here, we build two MOF/e-CRR systems, CoPc@NU-1000 and TPP(Co)@NU-1000, by installing cobalt metalated phthalocyanine and tetraphenylporphyrin electrocatalysts within the redox active NU-1000 MOF. For CoPc@NU-1000, the e-CRR responsive CoI/0 potential is close to that of NU-1000 reduction compared to the TPP(Co)@NU-1000. Efficient charge delivery, defined by a higher diffusion (Dhop =4.1×10-12 cm2 s-1 ) and low charge-transport resistance ( =59.5 Ω) in CoPC@NU-1000 led FECO =80 %. In contrast, TPP(Co)@NU-1000 fared a poor FECO =24 % (Dhop =1.4×10-12 cm2 s-1 and =91.4 Ω). For such a decoupling strategy, careful choice of the host framework is critical in pairing up with the underlying electrochemical properties of the catalysts to facilitate the charge delivery for its activation.