Solution-Processed Hydrogen-Bonded Organic Framework Nanofilms for High-Performance Resistive Memory Devices

Low-Power Memristor for Neuromorphic Computing: From Materials to Applications

As an emerging memory device, memristor shows great potential in neuromorphic computing applications due to its advantage of low power consumption. This review paper focuses on the application of low-power-based memristors in various aspects. The concept and structure of memristor devices are introduced. The selection of functional materials for low-power memristors is discussed, including ion transport materials, phase change materials, magnetoresistive materials, and ferroelectric materials. Two common types of memristor arrays, 1T1R and 1S1R crossbar arrays are introduced, and physical diagrams of edge computing memristor chips are discussed in detail. Potential applications of low-power memristors in advanced multi-value storage, digital logic gates, and analogue neuromorphic computing are summarized. Furthermore, the future challenges and outlook of neuromorphic computing based on memristor are deeply discussed.

Intrinsically Stretchable Resistive Memory Devices Utilizing Wavy Structured Strategy Integrated with Metal-Organic Framework Glasses

Flexible resistive random-access memory (RRAM) holds significant promise for data storage applications in the realms of smart healthcare and wearable devices. However, most research has focused primarily on the development of stretchable electrodes, frequently neglecting the mechanical compatibility between the functional layer and the electrode. Consequently, the advancement of intrinsically stretchable memristors presents a substantial challenge. Herein, a glassy metal-organic framework (MOF) film with a wrinkle structure is integrated with a pre-stretched electrode to fabricate intrinsically stretchable memristors. These devices demonstrate an impressive switching ratio of up to 105, a bending radius limit of 10 mm, and a strain limit of 20%, all while maintaining stable switching characteristics. Furthermore, conductive atomic force microscope (C-AFM) and focused ion beam (FIB) techniques reveal that the resistive switching effect is primarily governed by the silver conductive filament mechanism. This work successfully developed an intrinsically stretchable memristor, paving the way for the application of MOFs as functional layers in flexible electronics. It is expected to inspire further application of MOFs in the design of high-performance, flexible electronic technologies.

Hydrogen-Bonded Organic Framework Films Integrated with Wavy Structured Design for Wearable Bioelectronics

The integration of hydrogen-bonded organic frameworks (HOFs) with flexible electronic technologies offers a promising strategy for monitoring detailed health information, owing to their inherent porosity, excellent biocompatibility, and tunable catalytic capabilities. However, their application in wearable and real-time health monitoring remains largely unexplored, primarily due to the mechanical mismatch between the traditionally fragile HOFs particles and the softness of human skin. Herein, this study demonstrates an epidermal biosensor that maintains reliable sensing capability even under extreme deformation and complex environmental conditions by integrating HOFs films with wavy bioelectrodes. This wearable biosensor demonstrates ultrasensitive detection capabilities, with a limit of detection of 49.64 nM, and accurately measures nutritional content in sweat while conforming to curved skin surfaces. The sensor's performance is comparable to those obtained using high-performance liquid chromatography (HPLC). More strikingly, scratched HOFs films can be regenerated through a simple solvent rinsing process, enabling their reuse in the fabrication of new biosensors and offering a significant advantage over conventional sensing materials. This work has the potential to inspire the development of more flexible electronic devices, leveraging the structural adaptability and diversity of HOFs for personalized healthcare applications and real-time health monitoring.

Freestanding Hydrogen-Bonded Organic Framework Membrane for Efficient Wound Healing

Hydrogen-bonded organic frameworks (HOFs) are emerging as multifunctional materials with exceptional biocompatibility, abundant active sites, and tunable porosity, which are highly beneficial for advanced wound care. However, a significant challenge involves transforming pristine HOFs powders into lightweight, ultrathin, freestanding membranes compatible with soft biological systems. Herein, the study successfully develops shape-adaptive HOF-based matrix membranes (HMMs) using a polymer-assisted liquid-air interface technique. The HMMs conform seamlessly to tissues of different sizes and shapes, effectively stopping bleeding, and provide high water-vapor permeability. Notably, both in vitro and in vivo studies with mice wound models demonstrated that these tissue-conformable HMMs significantly accelerate wound healing by modulating the inflammatory environment of the injured tissue and promoting rapid re-epithelialization. Furthermore, RNA-seq analysis and mechanistic studies revealed that HMMs effectively reduce inflammation and facilitate the tissue transition from the proliferative stage to the remodeling stage of skin development. This work not only opens up new avenues for advanced wound care materials but also establishes a foundation for hybridizing HOFs with polymers for a wide range of potential applications.

In Situ Transformation of an Amorphous Supramolecular Coating to a Hydrogen-Bonded Organic Framework Membrane to Trigger Selective Gas Permeation

We introduce a "solution-processing-transformation" strategy, deploying solvent vapor as scaffolds, to fabricate high-quality hydrogen-bonded organic framework (HOF) membranes. This strategy can overcome the mismatch in processing conditions and crystal growth thermodynamics faced during the facile solution processing of the membrane. The procedure includes the vapor-trigged in situ transformation of dense amorphous supramolecules to crystalline HOF-16, with HOF-11 as the transient state. The mechanism involves a vapor-activated dissolution-precipitation equilibrium shifting and hydrogen bonding-guided molecule rearrangement, elucidated through combined experimental and theoretical analysis. Upon removal of the molecular scaffolds, the resulting HOF-16 membranes showcase significant improvement in hydrogen separation performance over their amorphous counterparts and previously reported HOF membranes. The method's broad applicability is evidenced by successfully extending it to other substrates and HOF structures. This study provides a fundamental understanding of guest-induced ordered supramolecular assembly and paves the way for the advanced manufacture of high-performance HOF membranes for gas separation processes.

Proton Conducting Neuromorphic Materials and Devices

Neuromorphic computing and artificial intelligence hardware generally aims to emulate features found in biological neural circuit components and to enable the development of energy-efficient machines. In the biological brain, ionic currents and temporal concentration gradients control information flow and storage. It is therefore of interest to examine materials and devices for neuromorphic computing wherein ionic and electronic currents can propagate. Protons being mobile under an external electric field offers a compelling avenue for facilitating biological functionalities in artificial synapses and neurons. In this review, we first highlight the interesting biological analog of protons as neurotransmitters in various animals. We then discuss the experimental approaches and mechanisms of proton doping in various classes of inorganic and organic proton-conducting materials for the advancement of neuromorphic architectures. Since hydrogen is among the lightest of elements, characterization in a solid matrix requires advanced techniques. We review powerful synchrotron-based spectroscopic techniques for characterizing hydrogen doping in various materials as well as complementary scattering techniques to detect hydrogen. First-principles calculations are then discussed as they help provide an understanding of proton migration and electronic structure modification. Outstanding scientific challenges to further our understanding of proton doping and its use in emerging neuromorphic electronics are pointed out.

Self-correcting mismatches in metastable hydrogen-bonded organic frameworks with an 11-fold interpenetrated array

The polymorphic self-correction from a metastable phase to a stable one often occurs and plays crucial roles in synthesizing robust hydrogen-bonded organic frameworks (HOFs). However, identifying metastable phases and understanding the self-correcting mechanisms is a challenging venture due to their intrinsic instability. Here, we for the first time introduce 1,8-naphtholactam (Np) as a hydrogen-bonding synthon positioned on the periphery of a bicarbazole to create a versatile molecular unit for 3D HOFs. The as-synthesized NCU-HOF1, analyzed by single-crystal X-ray diffraction (SCXRD), is found to be metastable. It exhibits an 11-fold interpenetrated dia topology with a quarter of the Np units exhibiting monomeric N-H⋯O interactions between adjacent Np link sites, which readily self-correct upon desolvation to form fully dimeric ones. Consequently, the resultant NCU-HOF1a becomes highly robust in polar solvents, strong acid or alkaline aqueous solutions, and has permanent porosity with contracted cavities for selective adsorption and efficient "turn-up" fluorescent sensing of C2H4 gas. This work not only debuts a new hydrogen-bonding synthon but offers more insights into investigating solid-state dynamics in metastable HOFs.

Optically Mediated Nonvolatile Resistive Memory Device Based on Metal-Organic Frameworks

Metal-organic frameworks (MOFs), characterized by tunable porosity, high surface area, and diverse chemical compositions, offer unique prospects for applications in optoelectronic devices. However, the prevailing research on thin-film devices utilizing MOFs has predominantly focused on aspects such as information storage and photosensitivity, often neglecting the integration of the advantages inherent in both photonics and electronics to enhance optical memory. This work demonstrates a light-mediated resistive memory device based on a highly oriented porphyrin-based MOFs film, in which the resistance state of the memristor is modulated by light, realizing the integration of the perception and storage of optical information. The memristor shows excellent performance with a wide light range of 405-785 nm and a persistent photoconductivity phenomenon up to 8.3 × 103 s. Further mechanistic studies have revealed that the resistive switching effect in the memristor is primarily associated with the reversible formation and annihilation of Ag conductive filaments.

Molecular-Potential and Redox Coregulated Cathodic Electrosynthesis toward Ionic Azulene-Based Thin Films for Organic Memristors

Organic memristors as promising electronic units are attracting significant attention owing to their simplicity of molecular structure design. However, fabricating high-quality organic films via novel synthetic technologies and exploring unprecedented chemical structures to achieve excellent memory performance in organic memristor devices are highly challenging. In this work, we report a cathodic electropolymerization to synthesize an ionic azulene-based memristive film (PPMAz-Py+Br-) under the molecular-potential and redox coregulation. During the cathodic electropolymerization process, electropositive pyridinium salts migrate to the cathode under an electric field, undergo a reduction-coupling deprotonation reaction, and polymerize into a uniform film with a controllable thickness on the electrode surface. The prepared Al/PPMAz-Py+Br-/ITO devices not only exhibit a high ON/OFF ratio of 1.8 × 103, high stability, long memory retention, and endurance under a wide range of voltage scans, but also achieve excellent multilevel storage and history-dependent memristive performance. In addition, the devices can mimic important biosynaptic functions, such as learning/forgetting function, synaptic enhancement/inhibition, paired-pulse facilitation/depression, and spiking-rate-dependent plasticity. The tunable memristive performances are attributed to the capture of free electrons on pyridinium cations, the migration of the aluminum ions (Al3+), and the form of Al conductive filaments under voltage scans.

Vapor-Phase Synthesis of Electrocatalytic Covalent Organic Frameworks

The inability to process many covalent organic frameworks (COFs) as thin films plagues their widespread utilization. Herein, a vapor-phase pathway for the bottom-up synthesis of a class of porphyrin-based COFs is presented. This approach allows integrating electrocatalysts made of metal-ion-containing COFs into the electrodes' architectures in a single-step synthesis and deposition. By precisely controlling the metal sites at the atomic level, remarkable electrocatalytic performance is achieved, resulting in unprecedentedly high mass activity values. How the choice of metal atoms, i.e., cobalt and copper, can determine the catalytic activities of POR-COFs is demonstrated. The theoretical data proves that the Cu site is highly active for nitrate conversion to ammonia on the synthesized COFs.

Supramolecular polynuclear clusters sustained cubic hydrogen bonded frameworks with octahedral cages for reversible photochromism

Developing supramolecular porous crystalline frameworks with tailor-made architectures from advanced secondary building units (SBUs) remains a pivotal challenge in reticular chemistry. Particularly for hydrogen-bonded organic frameworks (HOFs), construction of geometrical cavities through secondary units has been rarely achieved. Herein, a body-centered cubic HOF (TCA_NH4) with octahedral cages was constructed by a C3-symmetric building block and NH4+ node-assembled cluster (NH4)4(COOH)8(H2O)2 that served as supramolecular secondary building units (SSBUs), akin to the polynuclear SBUs in reticular chemistry. Specifically, the octahedral cages could encapsulate four homogenous haloforms including CHCl3, CHBr3, and CHI3 with truncated octahedron configuration. Crystallographic evidence revealed the cages served as spatially-confined nanoreactors, enabling fast, broadband photochromic effect associated with the reversible photo/thermal transformation between encapsulated CHI3 and I2. Overall, this work provides a strategy by shaping SSBUs to expand the framework topology of HOFs and a prototype of hydrogen-bonded nanoreactors to accommodate reversible photochromic reactions.

Orthogonal Postsynthetic Copolymerization of Hydrogen-Bonded Organic Frameworks into a PolyHOF Membrane

Hydrogen-bonded organic frameworks (HOFs) have shown promise in various fields; however, the construction of HOF/polymer hybrid membranes that can maintain both structural and functional integrity remains challenging. In this study, we here fabricated a new HOF (HOF-50) with reserved polymerizable allyl group via charge-assisted H-bonds between the carboxylate anion and amidinium, and subsequently copolymerized the HOF with monomers to construct a covalently bonded HOF/polymer hybrid (polyHOF) membrane. The resulting polyHOF membrane not only exhibits customizable mechanical properties and extreme stability, but also shows an exceptional ratiometric luminescent temperature-sensing function with very high sensitivity and visibility even when the lanthanide content is two orders of magnitude lower than that of the reported mixed-lanthanide metal-organic frameworks (MOFs) and lanthanide-doped covalent organic frameworks (COFs). This orthogonal postsynthesis copolymerization strategy may provide a general approach for preparing covalently connected HOF/polymer hybrid membranes for diverse applications.

Implementation of Thermal-Triggered Binary-Ternary Switchable Memory Performance in Zn/polysulfide/organic Complex-Based Memorizers by Finely Modulating the S62- Relaxation

Polysulfide-based multilevel memorizers are promising as novel memorizers, in which the occurrence of Sn2- relaxation is key for their multilevel memory. However, the effects of crystal packing and the side group of organic ligands on Sn2- relaxation are still ambiguous. In this work, ionic [Zn(S6)2·Zn2(Bipy)2SO4 (1), Zn(S6)2·Zn(Pmbipy)3 (2)] and neutral [ZnS6(Ombipy) (3), ZnS6(Phen)2 (4)] Zn/polysulfide/organic complexes with different packing modes and structures of organic ligands have been synthesized and were fabricated as memory devices. In both ionic and neutral Zn complexes, the S62- relaxation will be blocked by steric hindrances due to the packing of counter-cations and hydrogen-bond restrictions. Consequently, only the binary memory performances can be seen in FTO/1/Ag, FTO/2/Ag, and FTO/4/Ag, which originate from the more condensed packing of conjugated ligands upon electrical stimulus. Interestingly, FTO/3/Ag illustrates the unique thermally triggered reversible binary-ternary switchable memory performance. In detail, after introducing a methyl group on the 6'-position of bipyridine in ZnS6(Ombipy) (3), the ring-to-chain relaxation of S62- anions at room temperature will be inhibited, but it can happen at a higher temperature of 120 °C, which has been verified by elongated S-S lengths and the strengthened C-H···S hydrogen bond upon heating. The rules drawn in this work will provide a useful guide for the design of stimulus-responsive memorizers that can be applied in special industries such as automobile, oil, and gas industries.

Multistate structures in a hydrogen-bonded polycatenation non-covalent organic framework with diverse resistive switching behaviors

The inherent structural flexibility and reversibility of non-covalent organic frameworks have enabled them to exhibit switchable multistate structures under external stimuli, providing great potential in the field of resistive switching (RS), but not well explored yet. Herein, we report the 0D+1D hydrogen-bonded polycatenation non-covalent organic framework (HOF-FJU-52), exhibiting diverse and reversible RS behaviors with the high performance. Triggered by the external stimulus of electrical field E at room temperature, HOF-FJU-52 has excellent resistive random-access memory (RRAM) behaviors, comparable to the state-of-the-art materials. When cooling down below 200 K, it was transferred to write-once-read-many-times memory (WORM) behaviors. The two memory behaviors exhibit reversibility on a single crystal device through the temperature changes. The RS mechanism of this non-covalent organic framework has been deciphered at the atomic level by the detailed single-crystal X-ray diffraction analyses, demonstrating that the structural dual-flexibility both in the asymmetric hydrogen bonded dimers within the 0D loops and in the infinite π-π stacking column between the loops and chains contribute to reversible structure transformations between multi-states and thus to its dual RS behaviors.