Redox-Active Azulene-based 2D Conjugated Covalent Organic Framework for Organic Memristors

Acridinedione-phthalimide conjugates: Intramolecular electron transfer and singlet oxygen generation studies for optical and photodynamic therapy applications

We reported herein the synthesis, characterization of hybrid conjugates composed of phthalimide (Phth) and acridine-1,8-diones (Acr) for optical and medical applications. For the synthetic procedure, a three-step synthetic strategy has been utilized. The optical properties of the examined 1,8-acridinedione-phthalimide connected molecules (AcrPhth 1-5) have been examined utilizing various spectroscopic techniques, e.g., steady-state absorption and fluorescence, and time-correlated single photon counting. The steady-state absorption studies showed that AcrPhth 1-5 absorbs the light in the UV and visible region. The fluorescence studies of AcrPhth 1-5 exhibited significant fluorescence quenching compared to the acridinedione control compounds (Acr 1-5) suggesting the occurrence of electron-transfer reactions from the electron donating acridinedione moiety (Acr) to the electron accepting phthalimide moiety (Phth). The rate and efficiency of the electron-transfer reactions were determined from the fluorescence lifetime measurements indicating the fast electron-transfer processes of the covalently connected AcrPhth 1-5 conjugates. Computational studies supported the intramolecular electron-transfer reaction of AcrPhth conjugates using ab initio B3LYP/6-311G methods. In the optimized structures, the HOMO was found to be entirely located on the Acr entity, while the LUMO was found to be entirely on the Phth entity. Further, the synthesized compounds were tested as photosensitizers for generating the singlet oxygen species, which is a key factor in the photodynamic therapy (PDT) applications. The nanosecond laser flash measurements enable us to detect the triplet-excited states of examined Acr and AcrPhth conjugates, determining the triplet quantum yields, and direct detecting the singlet oxygen in an accurate way. From this observation, the singlet quantum yields were found to be in the range of 0.12-0.27 (for Acr 1-5) and 0.07-0.19 (for AcrPhth 1-5 conjugates). The molecular docking studies revealed that compound AcrPhth 2 exhibited high binding affinity with for key genes (p53, TOP2B, p38, and EGFR) suggesting its potential as a targeted anticancer therapy.

An Artificial Universal Tactile Nociceptor Based on 2D Polymer Film Memristor Arrays with Tunable Resistance Switching Behaviors

Nociceptor is an important receptor in the organism's sensory system; it can perceive harmful stimuli and send signals to the brain in order to protect the body in time. The injury degree of nociceptor can be divided into three stages: self-healing injury, treatable injury, and permanent injury. However, the current studies on nociceptor simulation are limited to the self-healing stage due to the limitation of the untunable resistance switching behavior of memristors. In this study, we constructed Al/2DPTPAK+TAPB/Ag memristor arrays with adjustable memory behaviors to emulate the nociceptor of biological neural network of all three stages. For this purpose, a PDMS/AgNWs/ITO/PET pressure sensor was assembled to mimic the tactile perception of the skin. The memristor arrays can not only simulate all the response of nociceptor, i.e., the threshold, relaxation, no adaptation, and sensitization with the self-healing injury, but can also simulate the treatable injury and the permanent injury. These behaviors are both demonstrated with a single memristor and in the form of pattern mapping of the memristor array.

One-Dimensional Covalent Organic Framework-Based Multilevel Memristors for Neuromorphic Computing

Memristors are essential components of neuromorphic systems that mimic the synaptic plasticity observed in biological neurons. In this study, a novel approach employing one-dimensional covalent organic framework (1D COF) films was explored to enhance the performance of memristors. The unique structural and electronic properties of two 1D COF films (COF-4,4'-methylenedianiline (MDA) and COF-4,4'-oxydianiline (ODA)) offer advantages for multilevel resistive switching, which is a key feature in neuromorphic computing applications. By further introducing a TiO2 layer on the COF-ODA film, a built-in electric field between the COF-TiO2 interfaces could be generated, demonstrating the feasibility of utilizing COFs as a platform for constructing memristors with tunable resistive states. The 1D nanochannels of these COF structures contributed to the efficient modulation of electrical conductance, enabling precise control over synaptic weights in neuromorphic circuits. This study also investigated the potential of these COF-based memristors to achieve energy-efficient and high-density memory devices.

Resistive Memristors Using Robust Electropolymerized Porous Organic Polymer Films as Switchable Materials

Porous organic polymers (POPs) with inherent porosity, tunable pore environment, and semiconductive property are ideally suitable for application in various advanced semiconductor-related devices. However, owing to the lack of processability, POPs are usually prepared in powder forms, which limits their application in advanced devices. Herein, we demonstrate an example of information storage application of POPs with film form prepared by an electrochemical method. The growth process of the electropolymerized films in accordance with the Volmer-Weber model was proposed by observation of atomic force microscopy. Given the mechanism of the electron transfer system, we verified and mainly emphasized the importance of porosity and interfacial properties of porous polymer films for memristor. As expected, the as-fabricated memristors exhibit good performance on low turn-on voltage (0.65 ± 0.10 V), reliable data storage, and high on/off current ratio (104). This work offers inspiration for applying POPs in the form of electropolymerized films in various advanced semiconductor-related devices.

2D Conjugated Polymer Thin Films for Organic Electronics: Opportunities and Challenges

2D conjugated polymers (2DCPs) possess extended in-plane π-conjugated lattice and out-of-plane π-π stacking, which results in enhanced electronic performance and potentially unique band structures. These properties, along with predesignability, well-defined channels, easy postmodification, and order structure attract extensive attention from material science to organic electronics. In this review, the recent advance in the interfacial synthesis and conductivity tuning strategies of 2DCP thin films, as well as their application in organic electronics is summarized. Furthermore, it is shown that, by combining topology structure design and targeted conductivity adjustment, researchers have fabricated 2DCP thin films with predesigned active groups, highly ordered structures, and enhanced conductivity. These films exhibit great potential for various thin-film organic electronics, such as organic transistors, memristors, electrochromism, chemiresistors, and photodetectors. Finally, the future research directions and perspectives of 2DCPs are discussed in terms of the interfacial synthetic design and structure engineering for the fabrication of fully conjugated 2DCP thin films, as well as the functional manipulation of conductivity to advance their applications in future organic electronics.

Porous organic framework membranes based on interface-induced polymerisation: design, synthesis and applications

Porous organic frameworks (POFs) are novel porous materials that have attracted much attention due to their extraordinary properties, such as high specific surface area, tunable pore size, high stability and ease of functionalisation. However, conventional synthesised POFs are mostly large-sized particles or insoluble powders, which are difficult to recycle and have low mass transfer efficiencies, limiting the development of their cutting-edge applications. Therefore, processing POF materials into membrane structures is of great significance. In recent years, interface engineering strategies have proved to be efficient methods for the formation of POF membranes. In this perspective, recent advances in the use of interfaces to prepare POF membranes are reviewed. The challenges of this strategy and the potential applications of the formed POF membranes are discussed.

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.

MoS2 Quantum Dot-Optimized Conductive Channels for a Conjugated Polymer-Based Synaptic Memristor

Donor-acceptor-type conjugated polymers are widely used in memristors due to their unique push-pull electron structures and charge transfer mechanisms. However, the inherently inhomogeneous microstructure of polymer films and their low crystallinity produce randomness that destabilizes formed conductive channels, giving polymer-based memristors unstable switching behavior. In this contribution, we prepared a synaptic device based on PM6-MoS2 QD (molybdenum disulfide quantum dot) nanocomposites. In the composites, MoS2 QDs provided the active centers for forming conductive channels via electron trapping and detrapping. They also controlled the directional formation of conductive channels between PM6 and MoS2 QDs, reducing randomness and giving devices a narrow switching voltage range and cycling longevity. The device exhibited continuous multistage conductance states under a direct current voltage sweep and simulated a variety of synaptic functions, including long-term potentiation, long-term depression, short-term potentiation, short-term depression, paired-pulse facilitation, spiking-rate-dependent plasticity, and "learning experience" behavior. The memristor could also perform arithmetic, including "counting" and "subtraction" operations. This work provides a new approach to improving the performance of memristors for neuromorphic computing.

Emerging Robust Polymer Materials for High-Performance Two-Terminal Resistive Switching Memory

Facing the era of information explosion and the advent of artificial intelligence, there is a growing demand for information technologies with huge storage capacity and efficient computer processing. However, traditional silicon-based storage and computing technology will reach their limits and cannot meet the post-Moore information storage requirements of ultrasmall size, ultrahigh density, flexibility, biocompatibility, and recyclability. As a response to these concerns, polymer-based resistive memory materials have emerged as promising candidates for next-generation information storage and neuromorphic computing applications, with the advantages of easy molecular design, volatile and non-volatile storage, flexibility, and facile fabrication. Herein, we first summarize the memory device structures, memory effects, and memory mechanisms of polymers. Then, the recent advances in polymer resistive switching materials, including single-component polymers, polymer mixtures, 2D covalent polymers, and biomacromolecules for resistive memory devices, are highlighted. Finally, the challenges and future prospects of polymer memory materials and devices are discussed. Advances in polymer-based memristors will open new avenues in the design and integration of high-performance switching devices and facilitate their application in future information technology.

Porous crystalline materials for memories and neuromorphic computing systems

Porous crystalline materials usually include metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs) and zeolites, which exhibit exceptional porosity and structural/composition designability, promoting the increasing attention in memory and neuromorphic computing systems in the last decade. From both the perspective of materials and devices, it is crucial to provide a comprehensive and timely summary of the applications of porous crystalline materials in memory and neuromorphic computing systems to guide future research endeavors. Moreover, the utilization of porous crystalline materials in electronics necessitates a shift from powder synthesis to high-quality film preparation to ensure high device performance. This review highlights the strategies for preparing porous crystalline materials films and discusses their advancements in memory and neuromorphic electronics. It also provides a detailed comparative analysis and presents the existing challenges and future research directions, which can attract the experts from various fields (e.g., materials scientists, chemists, and engineers) with the aim of promoting the applications of porous crystalline materials in memory and neuromorphic computing systems.

Convolution Neural Network-Assisted Smart Fluorescent-Tongue Based on Lanthanide Ion-Induced Forming MOF/HOF Composite for Differentiation of Flavor Compounds and Wine Identification

Wine flavor is a vital quality characteristic in wine, influenced by those flavor components with low sensory thresholds. It is crucial to recognize and classify the wine components related to their flavor contribution. The integration of fluorescent sensors and artificial intelligence shows huge potential in flavor recognition by emulation of the gustatory perception system. Meanwhile, achieving information identification of wine based on multiple information barcodes has hopeful applications in anticounterfeiting. In this study, we present a simple method in which organic linkers are weaved into a hydrogen-bonded organic framework (HOF) for the available transformation of a metal-bonded organic framework (MOF) induced by lanthanide ions (Ln3+). The fluorescent Ln-MOF/HOF composite exhibits high sensitivity, rapid response, and good recyclability for detecting seven flavor compounds in wine, including tannic acid, ionone, vanillin, anethole, anisaldehyde, hydroxybenzaldehyde, and 4-hydroxy-2-methylacetophenone. Depending on its satisfactory detectability, a novel strategy is provided in which a fluorescent sensor is able to function as a smart fluorescent-tongue (F-tongue) by the aid of convolutional neural network to differentiate these seven flavor compounds. In addition, the Ln-MOF/HOF composite has been used to prepare multiple information barcodes for wine information identification on the basis of dynamic fluorescence response toward tannic acid. The mimetic gustatory perception system developed in this study may offer a promising strategy for flavor recognition in food and further food anticounterfeiting.

Unravelling the Superiority of Nonbenzenoid Acepleiadylene as a Building Block for Organic Semiconducting Materials

Acepleiadylene (APD), a nonbenzenoid isomer of pyrene, exhibits a unique charge-separated character with a large molecular dipole and a small optical gap. However, APD has never been explored in optoelectronic materials to take advantage of these appealing properties. Here, we employ APD as a building block in organic semiconducting materials for the first time, and unravel the superiority of nonbenzenoid APD in electronic applications. We have synthesized an APD derivative (APD-IID) with APD as the terminal donor moieties and isoindigo (IID) as the acceptor core. Theoretical and experimental investigations reveal that APD-IID has an obvious charge-separated structure and enhanced intermolecular interactions as compared with its pyrene-based isomers. As a result, APD-IID displays significantly higher hole mobilities than those of the pyrene-based counterparts. These results imply the advantages of employing APD in semiconducting materials and great potential of nonbenzenoid polycyclic arenes for optoelectronic applications.

Covalent Organic Frameworks for Neuromorphic Devices

Neuromorphic computing could enable the potential to break the inherent limitations of conventional von Neumann architectures, which has led to widespread research interest in developing novel neuromorphic memory devices, such as memristors and bioinspired artificial synaptic devices. Covalent organic frameworks (COFs), as crystalline porous polymers, have tailorable skeletons and pores, providing unique platforms for the interplay with photons, excitons, electrons, holes, ions, spins, and molecules. Such features encourage the rising research interest in COF materials in neuromorphic electronics. To develop high-performance COF-based neuromorphic memory devices, it is necessary to comprehensively understand materials, devices, and applications. Therefore, this Perspective focuses on discussing the use of COF materials for neuromorphic memory devices in terms of molecular design, thin-film processing, and neuromorphic applications. Finally, we provide an outlook for future directions and potential applications of COF-based neuromorphic electronics.

Second order nonlinear optical properties of poled films containing azobenzenes tailored with azulen-1-yl-pyridine

Azo compounds, which are highly versatile molecules, have attracted a considerable attention both for their fundamental properties and for practical applications, especially in photonics. The conjugated azo-aromatic systems containing 4-(R-azulen-1-yl)-2,6-dimethyl-pyridine were investigated for their nonlinear optical properties. These molecules were embedded in polymethyl methacrylate (PMMA) matrix, and the obtained guest-host systems were processed into good optical quality thin film by spin coating technique. The dipolar moments of dissolved in PMMA molecules were oriented by applying a high DC electric field at a temperature close to the polymer glass transition temperature. The second - order nonlinear optical (NLO) properties of poled films were studied by the optical second harmonic generation technique (SHG). The poling kinetics, studied by in situ SHG as well as the measured second-order NLO susceptibilities of poled films are reported and discussed.