Hydrogen-bonded Organic Framework Research Articles

Encapsulation engineering of porous crystalline frameworks for delayed luminescence and circularly polarized luminescence.

Delayed luminescence (DF), including phosphorescence and thermally activated delayed fluorescence (TADF), and circularly polarized luminescence (CPL) exhibit common and broad application prospects in optoelectronic displays, biological imaging, and encryption. Thus, the combination of delayed luminescence and circularly polarized luminescence is attracting increasing attention. The encapsulation of guest emitters in various host matrices to form host-guest systems has been demonstrated to be an appealing strategy to further enhance and/or modulate their delayed luminescence and circularly polarized luminescence. Compared with conventional liquid crystals, polymers, and supramolecular matrices, porous crystalline frameworks (PCFs) including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), zeolites and hydrogen-bonded organic frameworks (HOFs) can not only overcome shortcomings such as flexibility and disorder but also achieve the ordered encapsulation of guests and long-term stability of chiral structures, providing new promising host platforms for the development of DF and CPL. In this review, we provide a comprehensive and critical summary of the recent progress in host-guest photochemistry via the encapsulation engineering of guest emitters in PCFs, particularly focusing on delayed luminescence and circularly polarized luminescence. Initially, the general principle of phosphorescence, TADF and CPL, the combination of DF and CPL, and energy transfer processes between host and guests are introduced. Subsequently, we comprehensively discuss the critical factors affecting the encapsulation engineering of guest emitters in PCFs, such as pore structures, the confinement effect, charge and energy transfer between the host and guest, conformational dynamics, and aggregation model of guest emitters. Thereafter, we summarize the effective methods for the preparation of host-guest systems, especially single-crystal-to-single-crystal (SC-SC) transformation and epitaxial growth, which are distinct from conventional methods based on amorphous materials. Then, the recent advancements in host-guest systems based on PCFs for delayed luminescence and circularly polarized luminescence are highlighted. Finally, we present our personal insights into the challenges and future opportunities in this promising field.

Stable hydrogen-bonded organic frameworks and their photo- and electro-responses

Stable hydrogen-bonded organic frameworks and their photo- and electro-responses

Vitrification-enabled enhancement of proton conductivity in hydrogen-bonded organic frameworks

Hydrogen-bonded organic frameworks (HOFs) are versatile materials with potential applications in proton conduction. Traditional approaches involve incorporating humidity control to address grain boundary challenges for proton conduction. This study finds vitrification as an alternative strategy to eliminate grain boundary effect in HOFs by rapidly melt quenching the kinetically stable HOF-SXU-8 to glassy state HOF-g. Notably, a remarkable enhancement in proton conductivity without humidity was achieved after vitrification, from 1.31 × 10−7 S cm−1 to 5.62× 10−2 S cm−1 at 100 °C. Long term stability test showed negligible performance degradation, and even at 30 °C, the proton conductivity remained at high level of 1.2 × 10−2 S cm−1. Molecule dynamics (MD) simulations and X-ray total scattering experiments reveal the HOF-g system is consisted of three kinds of clusters, i.e., 1,5-Naphthalenedisulfonic acid (1,5-NSA) anion clusters, N,N-dimethylformamide (DMF) molecule clusters, and H+-H2O clusters. In which, the H+ plays an important role to bridge these clusters and the high conductivity is mainly related to the H+ on H3O+. These findings provide valuable insights for optimizing HOFs, enabling efficient proton conduction, and advancing energy conversion and storage devices.

Enhancing Substrate Channeling with Multi-Enzyme Architectures in Hydrogen-Bonded Organic Framework.

Hydrogen-bonded organic frameworks (HOF) represent an emerging category of organic structures with high crystallinity and metal-free, which are not commonly observed in alternative porous organic frameworks. These needle-like porous structure can help in stabilizing enzymes and allow transfer of molecules between enzymes participating in cascade reactions for enhanced substrate channelling. Herein, we systematically synthesized and investigated the stability of HOF at extreme conditions followed by one-pot encapsulation of single and bi-enzyme systems. Firstly, we observed HOF to be stable at pH 1 to 14 and at high temperatures (up to 115°C). Secondly, the encapsulated glucose oxidase enzyme (GOX) showed 80 % and 90% of its original activity at 70 °C and pH 11, respectively. Thirdly, transient time close to 0 seconds was observed for HOF encapsulated bi-enzyme cascade reaction system demonstrating a 4.25-fold improvement in catalytic activity when compared to free enzymes with enhanced substrate channelling. Our findings showcase a facile system synthesized under ambient conditions to encapsulate and stabilize enzymes at extreme conditions.

Supramolecular Assembly Frameworks(SAFs): Shaping the Future of Functional Materials.

Supramolecular assembly frameworks (SAFs) represent a new category of porous materials, utilizing non-covalent interactions, setting them apart from metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). This category includes but is not restricted to hydrogen-bonded organic frameworks and supramolecular organic frameworks. SAFs stand out for their outstanding porosity, crystallinity, and stability, alongside unique dissolution-recrystallization dynamics that enable significant structural and functional modifications. Crucially, their non-covalent assembly strategies allow for a balanced manipulation of porosity, symmetry, crystallinity, and dimensions, facilitating the creation of advanced crystalline porous materials unattainable through conventional covalent or coordination bond synthesis. Despite their considerable promise in overcoming several limitations inherent to MOFs and COFs, particularly in terms of solution-processability, SAFs have received relatively little attention in recent literature. This Minireview aims to shed light on standout SAFs, exploring their design principles, synthesis strategies, and characterization methods. It emphasizes their distinctive features and the broad spectrum of potential applications across various domains, aiming to catalyze further development and practical application within the scientific community.

Iron modified hydrogen-bonded organic framework as fluorescent sensor for ascorbic acid detection

Herein, iron modified hydrogen-bonded organic framework (Fe-HOF) was successfully prepared by introducing the yellow-green fluorescent ligand 2,5-dihydroxyterephthalic acid into HOF and then modifying Fe3+. A simple turn-on fluorescence strategy is proposed for the detection of ascorbic acid (AA) based on Fe-HOF. Fe3+ could effectively quench fluorescence emission of HOF. In the presence of AA, Fe3+ was reduced to Fe2+, which led to the fluorescence recovery of HOF, thus realizing the fluorescence quantitative detection of AA. These fluorescence responsive behaviors of Fe-HOF ensure fluorescence assay of AA within 0.5 − 8 μM, along with a limit of detection (LOD) of 0.14 μM. The sensing platform could realize the rapid detection of ascorbic acid in vitamin C pills, tablets and beverages in the detection of ascorbic acid with good recoveries.

Enhancing catalytic activity through self-assembled hydrogen-bonded organic framework-based catalysts at liquid/liquid interface for 4-nitrophenol reduction and energy challenges in methanol fuel cell

Hydrogen-bonded organic frameworks (HOFs) are pure organic framework structures endowed with appropriate flexibility and porosity, which have attracted special attention in the field of energy and water, air, and soil remediation. In this study, six HOF-based materials were synthesized as thin film at the liquid/liquid (toluene/water) interface and characterized by FT-IR, Raman, UV–Vis, PXRD, ICP, AFM, SEM, TGA, and BET techniques. The self-assembled HOF-based thin films were employed as catalysts for the 4-nitrophenol removal from water medium and, for the first time, for methanol oxidation of fuel cell, with satisfying results. Simultaneous in situ catalyst formation and 4-nitrophenol reduction occurred in the case of Pt(0)@HOF thin film, but an extraordinary removal (not reduction) occurred in the presence of Pt(0)-trimesic acid thin film by formation of a new HOF from trimesic acid and 4-nitrophenol. Successful reduction of 4-nitrophenol occurred also in the presence of freshly prepared Pt(0)-trimesic acid, Pt(0)-melamine and Pt(0)@HOF catalysts (ex situ strategy). The chemical and thermal stability of HOF structure was improved by the interpenetration of ZIF-8 crystal structure, by increasing the hydrogen bonding and π-π stacking in the presence of 2-methylimidazole. The interpenetration of ZIF-8 to the crystal structure of HOF caused a significant decrease of the pore diameter of the structure. These pores acted as specific sites for the guest molecules, and their dimensions did not permit 4-nitrophenol to penetrate into the cavity of structures whereas allowed methanol penetration into these cavities due to its smaller size.

Hydrogen-bonded organic framework modified separator for simultaneously enhancing the safety and electrochemical performance of Ni-rich lithium-ion battery

Nickel-rich layered oxide cathode (LiNixCoyMn1−x−yO2, x > 0.5, NCM) shows substantial potential for applications in longer-range electrical vehicles. However, the rapid capacity decay and serious safety concerns impede its practical viability. This work provides a hydrogen-bonded organic framework (HOF) modification strategy to simultaneously improve the electrochemical performance, thermal stability and incombustibility of separator. Melamine cyanurate (MCA), as a low-cost and reliable flame-retardant HOF, was implemented in the separator modification layer, which can prevent the battery short circuit even at a high temperature. In addition, the supermolecule properties of MCA provide unique physical and chemical microenvironment for regulating ion-transport behavior in electrolyte. The MCA coating layer enabled the nickel-rich layered oxide cathode with a high-capacity retention of 90.3% after 300 cycles at 1.0 C. Collectively, the usage of MCA in lithium-ion batteries (LIBs) affords a simple, low-cost and efficient strategy to improve the security and service life of nickel-rich layered cathodes.

Ultrasensitive dual-mode detection of amyloid β oligomer via Au NRs modulated photoelectrochemical/electrochemiluminescent response from HOFs/g-C3N4

In this work, a heterojunction composite of HOFs/g-C3N4 was synthesized using solution-plasticized self-assembly of g-C3N4 nanosheet on hydrogen-bonded organic frameworks (HOFs). HOFs/g-C3N4 was then used as a substrate material to construct a novel photoelectrochemical/electrochemiluminescent (PEC/ECL) biosensor for the detection of amyloid β oligomer (Aβo). HOFs/g-C3N4 composites were first drop-coated on the electrode surface. Subsequently, the Aβ aptamer was modified on the electrode surface via amide bonding. The target Aβo and the gold nanorods (Au NRs)-labeled Aβ recognition peptide (Au NRs-KLVFF) were simultaneously dropped onto the electrode surface, thus a “sandwich” dual-mode biosensor was constructed. In the PEC detection of the Aβo, the surface plasmon resonance effect of Au NRs enhanced the visible absorption of HOF/g-C3N4, and the sensor exhibited a "signal-on" photocurrent signal. Meanwhile, the ECL emission spectrum of HOF/g-C3N4 in ECL mode overlaps with the ultraviolet-visible (UV) absorption of Au NRs, and the sensor signal showed a “signal-off” ECL response. Under the optimal conditions experiments, the constructed dual-mode biosensor showed a wide detection range and low detection limit for Aβo. The proposed dual-mode detection method has a detection range of 10 fM to 10 nM with a detection limit of 5.97 fM for PEC detection and a detection range of 0.1 pM to 1.0 μM with a detection limit of 0.051 pM for ECL detection respectively. Additionally, the detection method achieved satisfactory results in the analysis of real samples. Dual-mode sensing platform provides a new strategy for HOFs application in PEC/ECL assay and sensitive detection of AβO.

Hypoxia-Responsive Hydrogen-Bonded Organic Framework-Mediated Protein Delivery for Cancer Therapy.

The efficient delivery of therapeutic proteins to tumor sites is a promising cancer treatment modality. Hydrogen-bonded organic frameworks (HOFs) have been successfully used for the protective encapsulation of proteins; however, easy precipitation and lack of controlled release of existing HOFs limit their further application for protein delivery in vivo. In this study, a hypoxia-responsive HOF, self-assembled from azobenzenedicarboxylate/polyethylene glycol-conjugated azobenzenedicarboxylate and tetrakis(4-amidiniumphenyl)methane through charge-assisted hydrogen-bonding, is developed for systemic protein delivery to tumor cells. The newly generated HOF platform efficiently encapsulates representative cytochrome C, demonstrating good dispersibility under physiological conditions. Moreover, it can respond to overexpressed reductases in the cytoplasm under hypoxic conditions, inducing fast intracellular protein release to exert therapeutic effects. The strategy presented herein can be applied to other therapeutic proteins and can be expanded to encompass more intrinsic tumor microenvironment stimuli. This offers a novel avenue for utilizing HOFs in protein-based cancer therapy. This article is protected by copyright. All rights reserved.

Construction of Adaptive Deformation Block: Rational Molecular Editing of the N-Rich Host Molecule to Remove Water from the Energetic Hydrogen-Bonded Organic Frameworks.

Energetic hydrogen-bonded organic frameworks (E-HOFs), as a type of energetic material, spark fresh vitality to the creation of high energy density materials (HEDMs). However, E-HOFs containing cations and anions face challenges such as reduced energy density due to the inclusion of crystal water. In this work, the modification of amino groups in N-rich organic units could form a smart building block of hydrogen-bonded frameworks capable of changing the volume of the void space in the molecule through adaptive deformation of E-MOF blocks, thus enabling the replacement of water. Based on the above strategy, we report an interesting example of a series of hydrogen-bonded organic frameworks (E-HOF 2a and 3a) synthesized using a facile method. The crystal structure data of all of the compounds were also obtained in this work. Anhydrous 2a and 3a exhibit higher density, good thermal stability, and low mechanical sensitivity. The strategy of covalent bond modification for the host molecules of energetic frameworks shows enormous potential in eliminating the crystalline H2O of hydration and exploring high energy density materials.

Structural Design and Energy and Environmental Applications of Hydrogen-Bonded Organic Frameworks: A Systematic Review.

Hydrogen-bonded organic frameworks (HOFs) are emerging porous materials that show high structural flexibility, mild synthetic conditions, good solution processability, easy healing and regeneration, and good recyclability. Although these properties give them many potential multifunctional applications, their frameworks are unstable due to the presence of only weak and reversible hydrogen bonds. In this work, the development history and synthesis methods of HOFs are reviewed, and categorize their structural design concepts and strategies to improve their stability. More importantly, due to the significant potential of the latest HOF-related research for addressing energy and environmental issues, this work discusses the latest advances in the methods of energy storage and conversion, energy substance generation and isolation, environmental detection and isolation, degradation and transformation, and biological applications. Furthermore, a discussion of the coupling orientation of HOF in the cross-cutting fields of energy and environment is presented for the first time. Finally, current challenges, opportunities, and strategies for the development of HOFs to advance their energy and environmental applications are discussed.

Protein‐Integrated Hydrogen‐Bonded Organic Frameworks: Chemistry and Biomedical Applications

AbstractHydrogen‐bonded organic frameworks (HOFs) are porous nanomaterials that offer exceptional biocompatibility and versatility for integrating proteins for biomedical applications. This minireview concisely discusses recent advancements in the chemistry and functionality of protein‐HOF interfaces. It particularly focuses on strategic methodologies, such as the careful selection of building blocks and the genetic engineering of proteins, to facilitate protein‐HOF interactions. We examine the role of enzyme encapsulation within HOFs, highlighting its capability to preserve enzyme function, a crucial aspect for applications in biosensing and disease diagnosis. Moreover, we discuss the emerging utility of nanoscale HOFs for intracellular protein delivery, illustrating their applicability as nanoreactors for intracellular catalysis and neuroprotective biorthogonal catalysis within cellular compartments. We highlight the significant advancement of designing biodegradable HOFs tailored for cytosolic protein delivery, underscoring their promising application in targeted cancer therapies. Finally, we provide a perspective viewpoint on the design of biocompatible protein‐HOF assemblies, underlining their promising prospects in drug delivery, disease diagnosis, and broader biomedical applications.

Protein-Integrated Hydrogen-Bonded Organic Frameworks: Chemistry and Biomedical Applications.

Hydrogen-bonded organic frameworks (HOFs) are porous nanomaterials that offer exceptional biocompatibility and versatility for integrating proteins for biomedical applications. This minireview concisely discusses recent advancements in the chemistry and functionality of protein-HOF interfaces. It particularly focuses on strategic methodologies, such as the careful selection of building blocks and the genetic engineering of proteins, to facilitate protein-HOF interactions. We examine the role of enzyme encapsulation within HOFs, highlighting its capability to preserve enzyme function, a crucial aspect for applications in biosensing and disease diagnosis. Moreover, we discuss the emerging utility of nanoscale HOFs for intracellular protein delivery, illustrating their applicability as nanoreactors for intracellular catalysis and neuroprotective biorthogonal catalysis within cellular compartments. We highlight the significant advancement of designing biodegradable HOFs tailored for cytosolic protein delivery, underscoring their promising application in targeted cancer therapies. Finally, we provide a perspective viewpoint on the design of biocompatible protein-HOF assemblies, underlining their promising prospects in drug delivery, disease diagnosis, and broader biomedical applications.

Supramolecular Entanglement in a Hydrogen-Bonded Organic Framework Enables Flexible-Robust Porosity for Highly Efficient Purification of Natural Gas.

The development of porous materials with flexible-robust characteristics shows some unique advantages to target high performance for gas separation, but remains a daunting challenge to achieve so far. Herein, we report a carboxyl-based hydrogen-bonded organic framework (ZJU-HOF-8a) with flexible-robust porosity for efficient purification of natural gas. ZJU-HOF-8a features a four-fold interpenetrated structure withdiatopology, wherein abundant supramolecular entanglements are formed between the adjacent subnetworks through weak intermolecular hydrogen bonds. This structural configuration could stabilize the whole framework to establish the permanent porosity, but also enable the framework to show some flexibility(so-called flexible-robust framework). The flexible-robust porosity of ZJU-HOF-8a was confirmed by gas sorption isotherms and SCXRDstudies, showing that the flexible pore pockets can be opened by C3H8and n-C4H10rather by C2H6and CH4. This leads to notably higher C3H8and n-C4H10uptakes with enhanced selectivities than C2H6over CH4, affording one of the highest n-C4H10/CH4selectivities. The gas-loaded single-crystal structures coupled with theoretical simulations reveal that the loading of n-C4H10can induce an obvious framework expansion along with pore-pocket opening to improve n-C4H10uptake and selectivity, while not for C2H6adsorption. This work suggests an effective strategy of designing flexible-robust HOFs for improving gas separation properties.

Hydrogen‐Bonded Organic Framework Supporting Atomic Bi−N2O2 Sites for High‐Efficiency Electrocatalytic CO2 Reduction

AbstractSingle atomic catalysts (SACs) offer a superior platform for studying the structure–activity relationships during electrocatalytic CO2 reduction reaction (CO2RR). Yet challenges still exist to obtain well‐defined and novel site configuration owing to the uncertainty of functional framework‐derived SACs through calcination. Herein, a novel Bi−N2O2 site supported on the (1 1 0) plane of hydrogen‐bonded organic framework (HOF) is reported directly for CO2RR. In flow cell, the target catalyst Bi1‐HOF maintains a faradaic efficiency (FE) HCOOH of over 90 % at a wide potential window of 1.4 V. The corresponding partial current density ranges from 113.3 to 747.0 mA cm−2. And, Bi1‐HOF exhibits a long‐term stability of over 30 h under a successive potential‐step test with a current density of 100–400 mA cm−2. Density function theory (DFT) calculations illustrate that the novel Bi−N2O2 site supported on the (1 1 0) plane of HOF effectively induces the oriented electron transfer from Bi center to CO2 molecule, reaching an enhanced CO2 activation and reduction. Besides, this study offers a versatile method to reach series of M−N2O2 sites with regulable metal centers via the same intercalation mechanism, broadening the platform for studying the structure–activity relationships during CO2RR.

Efficient Multi-stimulus-Responsive Luminescent Eu(III)-Modified HOFs Materials: Detecting Thiram and Caffeic Acid and Constructing a Flexible Substrate Anti-counterfeiting Platform.

The powerful capability of multi-stimulus-responsive luminescent hydrogen-bonded organic frameworks (HOFs) to respond to external chemical or physical stimuli in various manners makes them appealing in the luminescence anti-counterfeiting field. Herein, a novel Eu3+-functionalized HOF (Eu@GC-2) that combines the emission of HOFs with the characteristic emission of Eu3+ ions has been successfully synthesized, which can generate various fluorescence at different excitation wavelengths. Eu@GC-2 has enormous potential as a raw material for a paper-based sensor that is designed for detecting the pesticides thiram and caffeic acid in crops with favorable selectivity, anti-interference, and high efficiency. Based on the above excellent properties, Ln3+-functionalized HOFs (Ln@GC-2) were then employed to produce four luminescent anti-counterfeiting inks. With the incorporation of back-propagation neural network and Gray code conversion functions, a multi-stimulus-responsive luminescent anti-counterfeiting platform, coregulated by the excitation light and the chemical reagent, has been constructed. This approach can not only achieve multiple encryptions and fast information identification but also enhance the code-breaking complexity, making it an efficient strategy for information encryption and decryption.

Artificial kagome lattices of Shockley surface states patterned by halogen hydrogen-bonded organic frameworks

Artificial electronic kagome lattices may emerge from electronic potential landscapes using customized structures with exotic supersymmetries, benefiting from the confinement of Shockley surface-state electrons on coinage metals, which offers a flexible approach to realizing intriguing quantum phases of matter that are highly desired but scarce in available kagome materials. Here, we devise a general strategy to construct varieties of electronic kagome lattices by utilizing the on-surface synthesis of halogen hydrogen-bonded organic frameworks (XHOFs). As a proof of concept, we demonstrate three XHOFs on Ag(111) and Au(111) surfaces, which correspondingly deliver regular, breathing, and chiral breathing diatomic-kagome lattices with patterned potential landscapes, showing evident topological edge states at the interfaces. The combination of scanning tunnelling microscopy and noncontact atomic force microscopy, complemented by density functional theory and tight-binding calculations, directly substantiates our method as a reliable and effective way to achieve electronic kagome lattices for engineering quantum states.

Structural, spectroscopic and computational studies of a new hydrogen-bonded organic framework containing carbazole moiety

A new hydrogen-bonded organic framework, CZ-1, containing a carbazole moiety was synthesized and characterized by SXRD, UV–Vis, FL and computational methods. SXRD analyses show that hydrogen bonding and π-π interactions are essential for the formation of its 3D supramolecular structure. IRI and NCI methods are used to analyze these weak interactions, while MPP and SDP descriptors are used to quantify the planarity of H3L in CZ-1. MEP highlighted nucleophilic and electrostatic regions in CZ-1, Hirshfeld surface analyses and RESP atomic charges visualized the interactions and depicted the charge distribution of H3L in CZ-1, respectively. The experimental and computed UV–Vis and FL spectra were compared using various density functional theory (DFT) functionals, with the PBE0 functional demonstrating the most accurate results. HOMO-LUMO and hole-electron analyses provided insights into the molecular electronic structure, enhancing the understanding of electronic excitation behavior within the molecule. Results from the RASPA program indicated that the porous structure of CZ-1 has the potential for adsorbing and separating CO2/N2 mixture.

Magnetic and Porous Regulation in Cobalt(II) Hydrogen-Bonded Organic Framework via Supramolecular Isomerism

Magnetic and Porous Regulation in Cobalt(II) Hydrogen-Bonded Organic Framework via Supramolecular Isomerism