Synthesis, Characterization, and Non-Volatile Memory Device Application of an N-Substituted Heteroacene

Modified Donor End Caps for Binary-to-Ternary WORM Memory Conversion in N-Heteroaromatic Systems

A series of novel D-π-A type organic small molecules have been designed, synthesized, and demonstrated for non-volatile resistive switching WORM memory application. The electron-deficient phenazine and quinoxaline units were coupled with various functionalized triphenylamine end caps to explore the structure-property correlations. The photophysical investigations displayed considerable intramolecular charge transfer, and the electrochemical analysis revealed an optimum band gap of 2.44 to 2.83 eV. These factors and the thin film morphological studies suggest the feasibility of the compounds as better resistive memory devices. All the compounds indicated potent non-volatile resistive switching memory capabilities with ON/OFF ratios ranging from 103 to 104, and the lowest threshold voltage recorded stands at -0.74 V. A longer retention time of 103 s marks the substantial stability of the devices. The phenazine-based compounds outperformed the others in terms of memory performance. Exceptionally, the compound with -CHO substituted triphenylamine exhibited ternary memory performance owing to its multiple traps. The resistive switching mechanism for the devices was validated using density functional theory calculations, which revealed that the integrated effect of charge transfer and charge trapping contributes significantly to the resistive switching phenomena.

Effect of terminal substituent of iso-indigo-based materials on the intermolecular stacking and memory performance

Attributed to the characteristics of narrow band gap structural units and full spectral response, iso-indigo is often used as an electron acceptor in organic electronic materials. Organic molecules with large conjugated surfaces and strong intermolecular forces can form ordered stacked structures through self-assembly. In this paper, the self-assembly performances of IDCF3 and IDCN are regulated by changing the end groups. The effects of terminal groups on the resistive memory behaviours and reproducibility are investigated. The properties of IDCF3 and IDCN devices are characterized by UV-VIS spectroscopy, cyclic voltammetry and DSC diffraction. The results show that when the end groups with different steric hindrance are introduced into the ends of the molecules with good backbone plane, the conjugated surfaces of the molecules will bend due to the different steric hindrance of the end groups in the form of cambium and layer-ordered packing, which will affect the threshold voltage and device reproducibility.

Electron-Sponge Nature of Polyoxometalates for Next-Generation Electrocatalytic Water Splitting and Nonvolatile Neuromorphic Devices

Designing next-generation molecular devices typically necessitates plentiful oxygen-bearing sites to facilitate multiple-electron transfers. However, the theoretical limits of existing materials for energy conversion and information storage devices make it inevitable to hunt for new competitors. Polyoxometalates (POMs), a unique class of metal-oxide clusters, have been investigated exponentially due to their structural diversity and tunable redox properties. POMs behave as electron-sponges owing to their intrinsic ability of reversible uptake-release of multiple electrons. In this review, numerous POM-frameworks together with desired features of a contender material and inherited properties of POMs are systematically discussed to demonstrate how and why the electron-sponge-like nature of POMs is beneficial to design next-generation water oxidation/reduction electrocatalysts, and neuromorphic nonvolatile resistance-switching random-access memory devices. The aim is to converge the attention of scientists who are working separately on electrocatalysts and memory devices, on a point that, although the application types are different, they all hunt for a material that could exhibit electron-sponge-like feature to realize boosted performances and thus, encouraging the scientists of two completely different fields to explore POMs as imperious contenders to design next-generation nanodevices. Finally, challenges and promising prospects in this research field are also highlighted.

Tuning Electrochemical Stability of 5,10-Ditolylphenazine-Based Antiaromatic Materials for Unipolar Memristor toward Artificial Synapses Application

Three organic conjugated small molecules, DTA-DTPZ, Cz-DTPZ, and DTA-me-DTPZ comprising an antiaromatic 5,10-ditolylphenazine (DTPZ) core and electron-donating peripheral substituents with high HOMOs (-4.2 to -4.7 eV) and multiple reversible oxidative potentials are reported. The corresponding films sandwiched between two electrodes show unipolar and switchable hysteresis current-voltage (I-V) characteristics upon voltage sweeping, revealing the prominent features of nonvolatile memristor behaviors. The numerical simulation of the I-V curves suggests that the carriers generated by the oxidized molecules lead to the increment of conductance. However, the accumulated carriers tend to deteriorate the device endurance. The electroactive sites are fully blocked in the dimethylated molecule DTA-me-DTPZ, preventing the irreversible electrochemical reaction, thereby boosting the endurance of the memristor device over 300 cycles. Despite the considerable improvement in endurance, the decrement of on/off ratio from 105 to 101 after 250 cycles suggests that the excessive charge carriers (radical cations) remains a problem. Thus, a new strategy of doping an electron-deficient material, CN-T2T, into the unipolar active layer was introduced to further improve the device stability. The device containing DTA-me-DTPZ:CNT2T (1:1) blend as the active layer retained the endurance and on/off ratio (∼104) upon sweeping 300 cycles. The molecular designs and doping strategy demonstrate effective approaches toward more stable metal-free organic conjugated small-molecule memristors.

Carbon Nanodots Memristor: An Emerging Candidate toward Artificial Biosynapse and Human Sensory Perception System

In the era of big data and artificial intelligence (AI), advanced data storage and processing technologies are in urgent demand. The innovative neuromorphic algorithm and hardware based on memristor devices hold a promise to break the von Neumann bottleneck. In recent years, carbon nanodots (CDs) have emerged as a new class of nano-carbon materials, which have attracted widespread attention in the applications of chemical sensors, bioimaging, and memristors. The focus of this review is to summarize the main advances of CDs-based memristors, and their state-of-the-art applications in artificial synapses, neuromorphic computing, and human sensory perception systems. The first step is to systematically introduce the synthetic methods of CDs and their derivatives, providing instructive guidance to prepare high-quality CDs with desired properties. Then, the structure-property relationship and resistive switching mechanism of CDs-based memristors are discussed in depth. The current challenges and prospects of memristor-based artificial synapses and neuromorphic computing are also presented. Moreover, this review outlines some promising application scenarios of CDs-based memristors, including neuromorphic sensors and vision, low-energy quantum computation, and human-machine collaboration.

High-Performance Flexible Polymer Memristor Based on Stable Filamentary Switching

Polymer-based atomic switch memristors via the formation/dissolution of atomic-scale conductive filaments are considered as the leading candidate for next-generation nonvolatile memory. However, the instability of conductive filaments of incomplete bridge makes their switching performances unsatisfied. In this work, we report a flexible polymeric memristor using polyethylenimine incorporated with silver salt. The memristor device exhibited superior performances at room temperature with a favorable endurance, high ON/OFF ratio, good retention, and low operating voltage. These satisfactory performances are attributed to the pre-existing Ag ions in the polymer, guiding the formation of a robust Ag filament. In addition, the device shows stable bipolar switching behavior in bending conditions or after hundreds of bending cycles. In our work, we provide a simple and efficient method to construct robust filament-based memristors for flexible electronics.

Dibenzo[d,d′]benzo[2,1-b:3,4-b′]difurans with extended π-conjugated chains: synthetic approaches and properties

Ru-Catalysed reaction of 3,8-di(hexyn-1-yl)dibenzo[d,d']benzo[2,1-b,3,4-b′]difuran [3,8-di(hexyn-1-yl)-DBBDF] with 2 equivalents of methyl (E)-penta-2,4-dienoate produces 3,8-bis[(1E,3E,5E)-2-butyl-6-methoxycarbonylhexa-1,3,5-trien-1-yl]-DBBDF (9a).

Azaacenes Based Electroactive Materials: Preparation, Structure, Electrochemistry, Spectroscopy and Applications-A Critical Review

This short critical review is devoted to the synthesis and functionalization of various types of azaacenes, organic semiconducting compounds which can be considered as promising materials for the fabrication of n-channel or ambipolar field effect transistors (FETs), components of active layers in light emitting diodes (LEDs), components of organic memory devices and others. Emphasis is put on the diversity of azaacenes preparation methods and the possibility of tuning their redox and spectroscopic properties by changing the C/N ratio, modifying the nitrogen atoms distribution mode, functionalization with electroaccepting or electrodonating groups and changing their molecular shape. Processability, structural features and degradation pathways of these compounds are also discussed. A unique feature of this review concerns the listed redox potentials of all discussed compounds which were normalized vs. Fc/Fc⁺. This required, in frequent cases, recalculation of the originally reported data in which these potentials were determined against different types of reference electrodes. The same applied to all reported electron affinities (EAs). EA values calculated using different methods were recalculated by applying the method of Sworakowski and co-workers (Org. Electron. 2016, 33, 300-310) to yield, for the first time, a set of normalized data, which could be directly compared.

Toward Highly Robust Nonvolatile Multilevel Memory by Fine Tuning of the Nanostructural Crystalline Solid-State Order

Organic resistive memory (ORM) offers great promise for next-generation high-density multilevel-cell (MLC) data storage. However, the fine tuning of crystalline order among its active layer still remains challenging, which largely restricts ORM behavior. Here, an exceptional solid-state transition from disordered orientations to highly-uniform orientation within the ORM layer is facilely triggered via molecular strategic tailoring. Two diketopyrrolopyrrole-based small molecular analogues (NI₁ TDPP and NI₂ TDPP) are demonstrated to display different symmetry. The asymmetric NI₁ TDPP shows an irregular solid-state texture, while the centro-symmetric NI₂ TDPP conforms to an ordered out-of-plane single-crystalline pattern that aligns with the foremost charge transportation along the substrate normal, and exhibits excellent MLC memory characteristics. Moreover, this highly oriented pattern guarantees the large-area film uniformity, leading to the twofold increase in the yield of as-fabricated ORM devices. This study reveals that the solid-state crystalline nanostructural order of organic materials can be controlled by reasonable molecular design to actuate high-performance organic electronic circuits.

Recent Progress in Polycyclic Aromatic Hydrocarbon-Based Organic Co-Crystals

Recently, the development of polycyclic aromatic hydrocarbon (PAH)-based organic co-crystals has attracted increasing interest due to their unique packing modes, optic-electronic properties and various potential applications in electronic, optic-electronic and magnetic devices. In this account, we mainly discuss the definition, classification, packing patterns, preparation methods, and applications of PAH-based co-crystals. Specifically, the main categories of PAH-based organic co-crystals, the frequent methods to prepare them, three main packing patterns, their optical and electrical properties, and their potential applications will be presented. Finally, an outlook of this field is provided.

Recent Progress in High Linearly Fused Polycyclic Conjugated Hydrocarbons (PCHs, n > 6) with Well-Defined Structures

Although polycyclic conjugated hydrocarbons (PCHs) and their analogues have gained great progress in the fields of organic photoelectronic materials, the in-depth study on present PCHs is still limited to hexacene or below because longer PCHs are insoluble, unstable, and tediously synthesized. Very recently, various strategies including on-surface synthesis are developed to address these issues and many higher novel PCHs are constructed. Therefore, it is necessary to review these advances. Here, the recent synthetic approach, basic physicochemical properties, single-crystal packing behaviors, and potential applications of the linearly fused PCHs (higher than hexacene), including acenes or π-extended acenes with fused six-membered benzenoid rings and other four-membered, five-membered or even seven-membered and eight-membered fused compounds, are summarized.

Benzoselenadiazole-Based Conjugated Molecules: Active Switching Layers with Nanofibrous Morphology for Nonvolatile Organic Resistive Memory Devices

In this work, two symmetrical donor-acceptor-donor (D-A-D) type benzoselenadiazole (BSeD)-based π-conjugated molecules were synthesized and employed as an active switching layer for non-volatile data storage applications. BSeD-based derivatives with different donor units attached through common vinylene linkers showed different electrical and optical properties. 4,7-Di((E)-styryl)benzo[c][2,1,3]selenadiazole (DSBSeD) and 4,7-bis((E)-4-methoxystyryl)benzo[c][2,1,3]selenadiazole (DMBSeD) are sandwiched between gallium-doped ZnO (GZO) and metal aluminum electrodes respectively through solution-processed spin-coating method. The solution-processed nanofibrous switching layer containing the DMBSeD-based memory device showed reliable memory characteristics in terms of write and erase operations with low SET voltage than the random-aggregated DSBSeD-based device. The nanofibrous molecular morphology of switching layer overcomes the interfacial hole transport energy barrier at the interface of the DMBSeD thin-film and the bottom GZO electrode. The memory device GZO/DMBSeD/Al based on nanofibrous switching layers shows switching characteristics at compliance current of 10 mA with V_set =0.79 V and V_reset =-0.55 V. This work will be beneficial for the rational design of advanced next-generation organic memory devices by controlling the nanostructured morphology of active organic switching layer for enhanced charge-transfer phenomenon.

Interfacial synthesis of a large-area coordination polymer membrane for rewritable nonvolatile memory devices

The facile synthesis of large-area coordination polymer membranes with controlled nanoscale thicknesses is critical towards their applications in information storage electronics. Here, we have reported a facile and substrate-independent interfacial synthesis method for preparing a large-area two-dimensional (2D) coordination polymer membrane at the air–liquid interface. The prepared high-quality 2D membrane could be transferred onto an indium tin oxide (ITO) substrate to construct a nonvolatile memory device, which showed reversible switching with a high ON/OFF current ratio of 10³, good stability and a long retention time. Our discovery of resistive switching with nonvolatile bistability based on the substrate-independent growth of the 2D coordination polymer membrane holds significant promise for the development of solution-processable nonvolatile memory devices with a miniaturized device size.

Stable nonvolatile memory devices with a high ON/OFF current ratio have been realized based on a large-area two-dimensional coordination polymer membrane.

Recent Progress in Organic Electron Transport Materials in Inverted Perovskite Solar Cells

Organic n-type materials (e.g., fullerene derivatives, naphthalene diimides (NDIs), perylene diimides (PDIs), azaacene-based molecules, and n-type conjugated polymers) are demonstrated as promising electron transport layers (ETLs) in inverted perovskite solar cells (p-i-n PSCs), because these materials have several advantages such as easy synthesis and purification, tunable frontier molecular orbitals, decent electron mobility, low cost, good solubility in different organic solvents, and reasonable chemical/thermal stability. Considering these positive factors, approaches toward achieving effective p-i-n PSCs with these organic materials as ETLs are highlighted in this Review. Moreover, organic structures, electron transport properties, working function of electrodes caused by ETLs, and key relevant parameters (PCE and stability) of p-i-n PSCs are presented. Hopefully, this Review will provide fundamental guidance for future development of new organic n-type materials as ETLs for more efficient p-i-n PSCs.

Efficient Inverted Perovskite Solar Cells by Employing N-Type (D-A1 -D-A2 ) Polymers as Electron Transporting Layer

It is highly desirable to employ n-type polymers as electron transporting layers (ETLs) in inverted perovskite solar cells (PSCs) due to their good electron mobility, high hydrophobicity, and simplicity of film forming. In this research, the capability of three n-type donor-acceptor₁ -donor-acceptor₂ (D-A₁ -D-A₂ ) conjugated polymers (pBTT, pBTTz, and pSNT) is first explored as ETLs because these polymers possess electron mobilities as high as 0.92, 0.46, and 4.87 cm² (Vs)^-1 in n-channel organic transistors, respectively. The main structural difference among pBTT, pBTTz, and pSNT is the position of sp² -nitrogen atoms (sp² -N) in the polymer main chains. Therefore, the effect of different substitution positions on the PSC performances is comprehensively studied. The as-fabricated p-i-n PSCs with pBTT, pBTTz, and pSNT as ETLs show the maximum photoconversion efficiencies of 12.8%, 14.4%, and 12.0%, respectively. To be highlighted, pBTTz-based device can maintain 80% of its stability after ten days due to its good hydrophobicity, which is further confirmed by a contact angle technique. More importantly, the pBTTz-based device shows a neglected hysteresis. This study reveals that the n-type polymers can be promising candidates as ETLs to approach solution-processed highly-efficient inverted PSCs.

Organic and hybrid resistive switching materials and devices

This review presents a timely and comprehensive summary of organic and hybrid materials for nonvolatile resistive switching memory applications in the “More than Moore” era, with particular attention on their designing principles for electronic property tuning and flexible memory performance.

Solvents Effects on Film Morphologies and Memory Behavior of a Perylenediimide-Containing Pendent Polymer

The large polydispersity index of functional pendant polymers has hindered their application in semiconductors. Herein, a novel pendant polymer with perylenediimide (PDI) in the side chains was successfully synthesized through ring-opening metathesis polymerization (ROMP) with a very low polydispersity index. The synthesized polymers were spin-coated on indium tin oxide (ITO) substrate by using a mixture of 1,2-dichlorobenzene (o-DCB) and methanol (MeOH) solvents. The surface morphologies and intermolecular π-π stacking of the fabricated film could be adjusted through tuning of the ratio of o-DCB and MeOH, and thus, the sandwich-structured device of ITO/polymer/aluminum exhibited different electrical behavior. The threshold voltages of the devices decreased as the MeOH content was increased from 0 to 30 % (v/v); however, the device changed from being unrewritable to rewritable if the MeOH content was increased to 40 %; a probable mechanism for this process is discussed. It is hoped that this new idea of synthesizing narrow polydispersity index pendant polymers, and the fabrication of high-quality films through the use of a mixture of solvents could allow high-performance memory devices to be prepared in the future.

Synthesis, Crystal Analysis, and Optoelectronic Properties of Diazole-Functionalized Acenes and Azaacenes

Doping heteroatoms into the skeletons of parent acenes can provide more opportunities to construct novel thermally and photostable organic π-conjugated semiconductors. Herein, a family of diazole-decorated acenes (APyS and APySe) and azaacenes (PyP, PyTh, PyPy, PyPh, and PyAP) have been successfully synthesized through the classical reactions. Single-crystal X-ray analyses showed that these as-formed diazole-modified derivatives adopted a twisted topology configuration, whereas the azaacenes display reclining-chair architectures, besides a twisted structure. All these compounds displayed yellow or red light in solution. Moreover, their electrochemical behaviors were also examined. We also found that the azaacenes exhibited a positive spectroscopic response to acid.

The Effect of Random and Block Copolymerization with Pendent Carbozole Donors and Naphthalimide Acceptors on Multilevel Memory Performance

Polymeric materials have been widely used in the fabrication of data-storage devices, owing to their unique advantages and defined conduction mechanisms. To date, the most-functional polymers that have been reported for memory devices were synthesized through random copolymerization, whilst there have been no reports regarding the memory effect of block polymers. Herein, we synthesized a random copolymer (PMCz₈ -co-PMBNa₂ ) and its corresponding block copolymer (PMCz₈ -b-PMBNa₂ ) to study the effect of the method of polymerization on the memory properties of the corresponding devices. Interestingly, both devices (ITO/PMCz₈ -co-PMBNa₂ /Al and ITO/PMCz₈ -b-PMBNa₂ /Al) exhibited ternary memory performance, with threshold voltages of -1.7 V/-3.3 V and -2.7 V/-3.8 V, respectively. However, based on comprehensive measurements, the memory properties of PMCz₈ -co-PMBNa₂ and PMCz₈ -b-PMBNa₂ were found to be owing to the operation of different conduction mechanisms, which resulted from different molecular stacking in the film state. Therefore, we expect that this work will be helpful for improving our understanding of the conduction mechanisms in polymer-based data-storage devices.

Recent Advances of Flexible Data Storage Devices Based on Organic Nanoscaled Materials

Following the trend of miniaturization as per Moore's law, and facing the strong demand of next-generation electronic devices that should be highly portable, wearable, transplantable, and lightweight, growing endeavors have been made to develop novel flexible data storage devices possessing nonvolatile ability, high-density storage, high-switching speed, and reliable endurance properties. Nonvolatile organic data storage devices including memory devices on the basis of floating-gate, charge-trapping, and ferroelectric architectures, as well as organic resistive memory are believed to be favorable candidates for future data storage applications. In this Review, typical information on device structure, memory characteristics, device operation mechanisms, mechanical properties, challenges, and recent progress of the above categories of flexible data storage devices based on organic nanoscaled materials is summarized.

Triboelectrification-Enabled Self-Powered Data Storage

Data storage by any means usually requires an electric driving power for writing or reading. A novel approach for self-powered, triboelectrification-enabled data storage (TEDS) is presented. Data are incorporated into a set of metal-based surface patterns. As a probe slides across the patterned surface, triboelectrification between the scanning probe and the patterns produces alternatively varying voltage signal in quasi-square wave. The trough and crest of the quasi-square wave signal are coded as binary bits of "0" and "1," respectively, while the time span of the trough and the crest is associated with the number of bits. The storage of letters and sentences is demonstrated through either square-shaped or disc-shaped surface patterns. Based on experimental data and numerical calculation, the theoretically predicted maximum data storage density could reach as high as 38.2 Gbit in-2. Demonstration of real-time data retrieval is realized with the assistance of software interface. For the TEDS reported in this work, the measured voltage signal is self-generated as a result of triboelectrification without the reliance on an external power source. This feature brings about not only low power consumption but also a much more simplified structure. Therefore, this work paves a new path to a unique approach of high-density data storage that may have widespread applications.

Changing molecular conjugation with a phenazine acceptor for improvement of small molecule-based organic electronic memory performance

Two small molecules with electron-accepting azobenzene or phenazine blocks, were synthesized. The experimental findings suggest that the molecule with larger conjugation may promote the memory performance by an enhanced strong charge transfer effect.

Evolutionary Metal Oxide Clusters for Novel Applications: Toward High-Density Data Storage in Nonvolatile Memories

Because of current fabrication limitations, miniaturizing nonvolatile memory devices for managing the explosive increase in big data is challenging. Molecular memories constitute a promising candidate for next-generation memories because their properties can be readily modulated through chemical synthesis. Moreover, these memories can be fabricated through mild solution processing, which can be easily scaled up. Among the various materials, polyoxometalate (POM) molecules have attracted considerable attention for use as novel data-storage nodes for nonvolatile memories. Here, an overview of recent advances in the development of POMs for nonvolatile memories is presented. The general background knowledge of the structure and property diversity of POMs is also summarized. Finally, the challenges and perspectives in the application of POMs in memories are discussed.

An all-in-one memory cell based on a homopolymer with a pyrene side chain and its volatile and nonvolatile resistive switch behaviors

Memory devices based on PMPPE exhibit a rewritable ternary memory behaviour (0, 1, 2, three conductivity states).

Nonvolatile resistive memories utilizing functional PES-based supramolecular film

This study reports the fabrication and characterization of polymer resistive switching memory devices fabricated from poly(ether sulfone)s (PESs), containing carboxylic functional groups for hydrogen bonding with disperse red 1. PES-based supramolecular memory devices exhibited write-once read-many-times-type memory effects, with low switching threshold voltages below −5.0 V and high ON/OFF current ratios of 105. It is the first time that the concept of azobenzene supramolecular PES based on hydrogen bonding for electrical memory device application was investigated. A possible switching mechanism based on the charge transfer interaction was proposed through molecular simulation, optical absorption, and cyclic voltammetry. These results render the PES-based supramolecular memory devices as promising components for high-performance polymer memory devices.

Composition-dependent nanoelectronics of amido-phenazines: non-volatile RRAM and WORM memory devices

A metal-free three component cyclization reaction with amidation is devised for direct synthesis of DFT-designed amido-phenazine derivative bearing noncovalent gluing interactions to fabricate organic nanomaterials. Composition-dependent organic nanoelectronics for nonvolatile memory devices are discovered using mixed phenazine-stearic acid (SA) nanomaterials. We discovered simultaneous two different types of nonmagnetic and non-moisture sensitive switching resistance properties of fabricated devices utilizing mixed organic nanomaterials: (a) sample-1(8:SA = 1:3) is initially off, turning on at a threshold, but it does not turn off again with the application of any voltage, and (b) sample-2 (8:SA = 3:1) is initially off, turning on at a sharp threshold and off again by reversing the polarity. No negative differential resistance is observed in either type. These samples have different device implementations: sample-1 is attractive for write-once-read-many-times memory devices, such as novel non-editable database, archival memory, electronic voting, radio frequency identification, sample-2 is useful for resistive-switching random access memory application.

Thermoresponsive Memory Behavior in Metallosupramolecular Polymer-Based Ternary Memory Devices

Thermal-sensitive materials, such as metallosupramolecular polymers, have been integrated into devices for a broad range of applications. However, the role of these materials is limited to temperature sensing and the lack of a memory function. Herein, we present novel [PolyCo-L1_xL2_y-PF₆]-based organic resistive memories (ORMs) possessing both a thermal response and ternary memory behavior with three electrical resistance states [high (HRS), intermediate (IRS), and low (LRS)]. Furthermore, the thermal behavior can be memorized by the Al/[PolyCoL1_xL2_y-PF₆]/indium-tin oxide devices. Heating and cooling the devices at a LRS results in a switch from the LRS to a HRS and further to a LRS, indicating that the thermal behavior can be efficiently memorized. Following the heating and cooling process, devices at a HRS retain their ternary memory behavior, while an unstable resistance variation behavior is observed at the IRS. We propose a possible mechanism for the thermoresponsive memory behavior, and this finding provides a guide for the design of future thermoresponsive ORMs.

Synthesis, Optoelectronic and Self-Assembly Properties of Diazadioxaacene Derivatives

Two novel diazadioxaacene derivatives (ADOP and ADOQ) have been successfully synthesized and characterized. Their single crystal analyses disclose that molecule ADOP forms a twisted topology configuration, whereas ADOQ adopts reclining-chair architecture. Both of them emit strong blue fluorescence in organic solvents. Moreover, they can self-assemble to form regular nanobelts and nanowires, respectively, via a simple surfactant-assisted method.

Fluorine-Induced Highly Reproducible Resistive Switching Performance: Facile Morphology Control through the Transition between J- and H-Aggregation

Improving the reproducibility and air-endurance of organic resistance switching (RS) devices, in particular multilevel-cell RS devices, is critical for the confirmation of its competency to realize big data storage capability. However, such enhancement still remains challenging. In this report, we demonstrated that fluorine (F)-embedding should be an effective way to enhance the overall performance of RS devices. Four new azo-cored analogues (IDAZO, FIDAZO, F₂IDAZO, and F₄IDAZO) have been designed and synthesized. These four compounds have similar structures with different numbers of F substituents. Interestingly, UV-vis measurements reveal that upon F-embedding, an exceptional transition from molecular J-aggregation to H-aggregation is achieved. As a result, the morphology of RS films becomes more and more uniform, as determined by AFM and XRD. Meanwhile, the hydrophobicity of RS film is promoted, which further improves the device atmospheric stability. The total RS reproducibility increases to 96% (the uppermost value), and the tristage RS reproducibility rises to 64%, accompanied by a more stable OFF state and lower logic SET voltages. Our study suggests F-embedding would be a promising strategy to achieve highly reproducible and air-endurable organic multilevel-cell RS devices.

Synthesis, Physical Properties and Memory Device Application of a Twelve-Ring Fused Twistheteroacene

Developing new organic conjugated materials for high density memory devices is highly desirable. In this research, a novel donor-acceptor-type twelve-ring fused twistheteroacene, 2,7,19,24-tetra-tert-butyl-13,30-didodecyl-9,17,26,34-tetraphenyl benzo[8',9']triphenyleno[2',3':7,8]dibenzo[b,e][1,4]dioxino[1,2,3,4-lmn]dibenzo[6',7':10',11']tetraceno[2',3':5,6][1,4]dioxino[2,3-f][3,8]phenanthroline-12,14,29,31(13H,30H)-tetraone (DPyN) has been synthesized and characterized. It displays high thermal stability, possesses a broad absorption band centered at 510 and 538 nm, and emits red fluorescence in organic solvents. A solution-processed memory device with DPyN as an active element shows an excellent memory performance with an ON/OFF current ratio of 10^3.46 :1 and a threshold voltage of -2.44 V.