A Phosphole Oxide-Containing Organogold(III) Complex for Solution-Processable Resistive Memory Devices with Ternary Memory Performances

Pd-catalysed C-H alkynylation of benzophospholes

A palladium-catalysed C2-H alkynylation of benzophospholes with alkynyl bromides has been developed to afford the corresponding phosphole-alkyne conjugations in good to high yields. The C-C triple bond as well as terminal alkyne C-H bond in the obtained products is a good synthetic handle for further manipulations, thus giving the versatile π-conjugated benzophosphole derivatives. The optoelectronic properties of the newly synthesized conjugated benzophospholes are also described.

Synapse-Mimicking Memristors Based on 3,6-Di(tpy)-9-Phenylcarbazole Unimer and Its Copolymer with Cobalt(II) Ions

The title compound, unimer U (tpy stands for 2,2':6',2″-terpyridin-4'-yl end-group), by itself shows the memristor effect with a retention time of 18 h and persistence of 11 h. Its coordination copolymer with Co(II) ions, [CoU]n, exhibits multimodal resistance changes similar to the synaptic responses observed in biological systems. More than 320 cycles of potentiation and depression measured in continuous sequence occurred without observing a significant current change, confirming the operational stability and reproducibility of the device based on the [CoU]n polymer. The synaptic effect of a device with an indium tin oxide (ITO)/[CoU]n/top-electrode (TE) configuration is more pronounced for the device with TE = Au compared to devices with TE = Al or Ga. However, the latter TEs provide a cost-effective approach without any significant compromise in device plasticity. The detected changes in the synaptic weight, about 12% for pair-pulse facilitation and 80% for its depression, together with a millisecond trigger and reading pulses that decay exponentially on the time scale typical of neurosynapses, justify the device's ability to learn and memorize. These properties offer potential applications in neuromorphic computation and brain-inspired synaptic devices.

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.

Design and synthesis of a solution-processed redox-active bis(formazanate) zinc complex for resistive switching applications

In this paper, we report the synthesis and characterization of a mononuclear zinc complex (1) containing a redox-active bis(4-antipyrinyl) derivative of the 3-cyanoformazanate ligand. Complex 1 was readily obtained by refluxing zinc acetate with 3-cyano-1,5-(4-antipyrinyl)formazan (LH) in a methanolic solution. Single-crystal X-ray diffraction analysis of complex 1 shows that the formazanate ligands bind to the zinc center in a five-member chelate "open" form via the 1- and 4-positions of the 1,2,4,5-tetraazapentadienyl formazanate backbone leading to the formation of the mononuclear bis(formazanate) zinc complex exhibiting a distorted octahedral geometry. We also report the study of resistive-switching random access memory application of this solution-processable bis(formazanate) Zn(II) complex to facilitate the practical implementation of transition metal complex-based molecular memory devices. The complex demonstrated high conductance switching with a large ON-OFF ratio, good stability, and a long retention time. A trap-controlled space charge limited current mechanism is proposed for the observed resistive switching behavior of the device, wherein the role played by the [ZnIIL2] complex that comprises the extended redox-active conjugated ligand backbone is revealed by corroborating electrochemical studies, spectrochemical experiments, and DFT calculations. In addition to providing significant insights into the molecular design of transition metal complexes for memory applications, this study also presents the utilization of ZnIIL2 towards the realization of non-volatile resistive random access memory (RRAM) devices with inorganic/organic hybrid active layers that are highly cost-effective and sustainable. These devices exhibited multilevel switching and low current operation, both of which are desirable for advanced memory applications.

Many-Body Molecular Interactions in a Memristor

Electronic transitions in molecular-circuit elements hinge on complex interactions between molecules and ions, offering a multidimensional parameter space to embed, access, and optimize material functionalities for target-specific applications. This opportunity is not cultivated in molecular memristors because their low-temperature charge transport, which is a route to decipher molecular many-body interactions, is unexplored. To address this, robust, temperature-resilient molecular memristors based on a Ru complex of an azo aromatic ligand are designed, and current-voltage sweep measurements from room temperature down to 2 K with different cooling protocols are performed. By freezing out or activating different components of supramolecular dynamics, the local Coulombic interactions between the molecules and counterions that affect the electronic transport can be controlled. Operating conditions are designed where functionalities spanning bipolar, unipolar, nonvolatile, and volatile memristors with sharp as well as gradual analog transitions are captured within a single device. A mathematical design space evolves, thereof comprising 36 tuneable parameters in which all possible steady-state functional variations in a memristor characteristic can be attainable. This enables a deterministic design route to engineer neuromorphic devices with unprecedented control over the transformation characteristics governing their functional flexibility and tunability.

Switching the memory behaviour from binary to ternary by triggering S62- relaxation in polysulfide-bearing zinc-organic complex molecular memories

The use of crystalline metal-organic complexes with definite structures as multilevel memories can enable explicit structure-property correlations, which is significant for designing the next generation of memories. Here, four Zn-polysulfide complexes with different degrees of conjugation have been fabricated as memory devices. ZnS₆(L)₂-based memories (L = pyridine and 3-methylpyridine) can exhibit only bipolar binary memory performances, but ZnS₆(L)-based memories (L = 2,2'-bipyridine and 1,10-phenanthroline) illustrate non-volatile ternary memory performances with high ON2/ON1/OFF ratios (10^4.22/10^2.27/1 and 10^4.85/10^2.58/1) and ternary yields (74% and 78%). Their ON1 states stem from the packing adjustments of organic ligands upon the injection of carriers, and the ON2 states are a result of the ring-to-chain relaxation of S₆^2- anions. The lower conjugated degrees in ZnS₆(L)₂ result in less compact packing; consequently, the adjacent S₆^2- rings are too long to trigger the S₆^2- relaxation. The deep structure-property correlation in this work provides a new strategy for implementing multilevel memory by triggering polysulfide relaxation based on the conjugated degree regulation of organic ligands.

A 3D multistage information encryption platform with self-erasure function based on a synergistically shape-deformable and AIE fluorescence-tunable hydrogel

The traditional stored information is statically shown on single 2D planes, which leads to low information storage capacity and secondary information leakage without the proper handling of decrypted information. Developing a 3D multistage information encryption platform with self-erasure function is highly desirable. Here, a novel bilayer hydrogel with synergistic deformation and fluorescence color (SDFC) change is designed for 3D multistage information encryption. The bilayer hydrogel consisting of a shape-deformable hydrogel layer and a fluorescence hydrogel layer with aggregation-induced emission (AIE) properties can exhibit pH-responsive SDFC change. Fluorescence information can be ionoprinted on the fluorescent hydrogel layer based on electrostatic interactions and dynamic covalent bonds. The 2D bilayer hydrogel encoded with information can synergistically produce predesigned 3D shape configuration and enhanced background fluorescence to wrap information, which is only readable after sequential shape recovery with the disappearance of background fluorescence. Furthermore, multistage information can be further obtained by stepwise decryption due to information with differential fluorescence fading rates. The displayed information is automatically self-erased in the end, avoiding the information secondary leakage. This study paves an avenue for broadening conventional 2D single-level information encryption platforms to 3D multistage counterparts with self-erasure and multi-decryption capabilities based on SDFC change of the bilayer hydrogel.

Redox Switching Behavior in Resistive Memory Device Designed Using a Solution-Processable Phenalenyl-Based Co(II) Complex: Experimental and DFT Studies

We herein report a novel square-planar complex [Co^IIL], which was synthesized using the electronically interesting phenalenyl-derived ligand LH₂ = 9,9'-(ethane-1,2-diylbis(azanediyl))bis(1H-phenalen-1-one). The molecular structure of the complex is confirmed with the help of the single-crystal X-ray diffraction technique. [Co^IIL] is a mononuclear complex where the Co(II) ion is present in the square-planar geometry coordinated by the chelating bis-phenalenone ligand. The solid-state packing of [Co^IIL] complex in a crystal structure has been explained with the help of supramolecular studies, which revealed that the π···π stacking present in the [Co^IIL] complex is analogous to the one present in tetrathiafulvalene/tetracyanoquinodimethane charge transfer salt, well-known materials for their unique charge carrier interfaces. The [Co^IIL] complex was employed as the active material to fabricate a resistive switching memory device, indium tin oxide/Co^IIL/Al, and characterized using the write-read-erase-read cycle. The device has interestingly shown a stable and reproducible switching between two different resistance states for more than 2000 s. Observed bistable resistive states of the device have been explained by corroborating the electrochemical characterizations and density functional theory studies, where the role of the Co^II metal center and π-conjugated phenalenyl backbone in the redox-resistive switching mechanism is proposed.

Synthesis, Structures, and Properties of π-Extended Phosphindolizine Derivatives

Dibenzo[b,g]phosphindolizine oxide and three types of benzo[e]naphthophosphindolizine oxides have been synthesized by the ring-closing metathesis of benzo[b]phosphole oxide and naphthophosphole oxides with two olefin tethers. Their molecular structures and properties were revealed by X-ray crystallographic analysis, UV-vis spectroscopy, and electrochemical analysis. The number and position of the benzene rings were found to alter the structural geometry and the HOMO/LUMO energy levels, and their effects were investigated by theoretical calculations. Among the phosphindolizine oxide derivatives investigated, only benzo[e]naphtho[2,3-b]phosphindolizine oxide with the naphthalene ring fused at 2,3-positions showed weak yellow fluorescence with a large Stokes shift.

Effective Transport Tunnels Achieved by 1,2,4,5-Tetrazine-Induced Intermolecular C-H...N Interaction and Anion Radicals for Stable ReRAM Performance

The D-A structured small-molecule-based resistive random-access memory (ReRAM) device has been well-researched in the last decade, and the switching mechanism was mainly induced by the intramolecular/intermolecular charge transfer processes from the donors to the acceptors. However, in the previous work, some small molecules with pristine electron acceptors in the backbone could still show the typical memory behaviors, of which the switching mechanism is still ambiguous. In this work, two 1,2,4,5-tetrazine based n-type small-molecular isomers, 2-DPTZ and 4-DPTZ, with the same electron acceptor, 1,2,4,5-tetrazine and pyridine, are chosen to investigate the isomeric effects on molecular packing, switching mechanism, and memory performance. Because of the abundant nitrogen atoms with a localized lone pair of electrons in the sp² orbital, 2-DPTZ and 4-DPTZ compounds could self-assemble into a long-range ordered molecular packing through intermolecular C-H...N interactions, affording effective transporting tunnels for charge-carrier transport. As expected, the sandwich-structured ITO/2-DPTZ or 4-DPTZ/Al memory devices both showed binary memory characteristics, with 2-DPTZ based memory devices showing the write once read many times (WORM) memory behavior and 4-DPTZ based memory devices having the negative differential resistance (NDR) memory performance. These distinct ReRAM properties arose from the different morphologies of 2-DPTZ and 4-DPTZ films that were induced by the different packing styles between the adjacent molecules, as confirmed by X-ray diffraction (XRD) and tapping-mode atomic force microscopy (AFM) height images. Most importantly, the switching mechanism was thought to be attributed to the injected electrons that reduced the neutral molecules of 2-DPTZ and 4-DPTZ to their corresponding anion radicals. Thus, this present work helps us better understand the conducting mechanism of small molecules with pristine electron acceptors in the backbone and provides a supplementary guideline for designing multilevel small molecules to match the structure-stacking-property relationship.

Metal-containing organic compounds for memory and data storage applications

With the upcoming trend of Big Data era, some new types of memory technologies have emerged as substitutes for the traditional Si-based semiconductor memory devices, which are encountering severe scaling down technical obstacles. In particular, the resistance random access memory (RRAM) and magnetic random access memory (MRAM) hold great promise for the in-memory computing, which are regarded as the optimal strategy and pathway to solve the von Neumann bottleneck by high-throughput in situ data processing. As far as the active materials in RRAM and MRAM are concerned, organic semiconducting materials have shown increasing application perspectives in memory devices due to their rich structural diversity and solution processability. With the introduction of metal elements into the backbone of molecules, some new properties and phenomena will emerge accordingly. Consequently, the RRAM and MRAM devices based on metal-containing organic compounds (including the small molecular metal complexes, metallopolymers, metal-organic frameworks (MOFs) and organic-inorganic-hybrid perovskites (OIHPs)) have been widely explored and attracted intense attention. In this review, we highlight the fundamentals of RRAM and MRAM, as well as the research progress of the applications of metal-containing organic compounds in both RRAM and MRAM. Finally, we discuss the challenges and future directions for the research of organic RRAM and MRAM.

Ternary Conductance Switching Realized by a Pillar[5]arene-Functionalized Two-Dimensional Imine Polymer Film

Nowadays, most manufacturing memory devices are based on materials with electrical bistability (i. e., "0" and "1") in response to an applied electric field. Memory devices with multilevel states are highly desired so as to produce high-density and efficient memory devices. Herein, we report the first multichannel strategy to realize a ternary-state memristor. We make use of the intrinsic sub-nanometer channel of pillar[5]arene and nanometer channel of a two-dimensional imine polymer to construct an active layer with multilevel channels for ternary memory devices. Low threshold voltage, long retention time, clearly distinguishable resistance states, high ON/OFF ratio (OFF/ON1/ON2=1 : 10 : 10³ ), and high ternary yield (75 %) were obtained. In addition, the flexible memory device based on 2DP_TPAZ+TAPB can maintain its stable ternary memory performance after being bent 500 times. The device also exhibits excellent thermal stability and can tolerate a temperature as high as 300 °C. It is envisioned that the results of this work will open up possibilities for multistate, flexible resistive memories with good thermal stability and low energy consumption, and broaden the application of pillar[n]arene.

Memristors Based on an Iridium(III) Complex Containing Viologen for Advanced Synaptic Bionics

Memristors with nonvolatile memory properties are expected to open the era of neuromorphic computing. However, it remains a huge challenge to develop memristors with high uniformity, high stability, and low power consumption for advanced synaptic bionics. Herein, an electroactive iridium(III) complex Ir-vio was designed and synthesized by incorporating a viologen moiety into its N^∧N ligand. Complex Ir-vio showed multiple redox states and high sensitivity to an electrical stimulus. Importantly, two-terminal memristors with Ag/Ir-vio/W structure were successfully fabricated by the solution-processable method, which exhibited multilevel storage characteristics with a low switching threshold voltage of 0.5 V and high ON1/ON2/ON3/OFF current ratio of 10⁵/10³/10²/1 at a low reading bias of 0.05 V. Moreover, the memristors can mimic synaptic plasticity, indicating that they can act as artificial synapses to construct brain-inspired neural networks. The memristive mechanisms can be ascribed to the interconversion among different charge-transfer and redox states under various electrical stimulus. To the best of our knowledge, this work is the first experimental demonstration of memristors based on iridium(III) complexes, opening a new era for the development of synaptic bionic devices based on organometallic compounds.

Irreversible Resistive State Switching in Devices with a Homoleptic Cobalt(II) Complex Active Layer

Molecules with bi-stable electronic transport behaviour have been in upfront research topics of the molecular semiconductor devices in the past few decades due to the use of such materials in resistive data storage devices. Transition metal complexes (TMC) are expected to be potential candidates in regard to the tunable and manifold redox behaviour expecting multiple bulk transport states. Finding alternate mechanisms in such devices with TMC as the active layer materials would revoke the multifaceted approach to the functional gain. We have succeeded in demonstrating write once-read many (WORM) type of resistive memory device using a homoleptic Cobalt(II) (Co(II)) complex with large on/off current ratio ensuring the easy readout process at lower voltage. The advantage of this device was the turn on voltage was found to be the low (<2.7 V) operational voltage and the success ratio of the devices were more than 83%. The durability of the stored data was found to be more than 35,000 seconds which ensures the stability of the bistable state in the fabricated devices. Such ambient stable, solution processable devices are important for the large-scale printable devices. The manuscript describes the preparation, optical and electrochemical characterisation of the metal complex used along with a detailed mechanistic investigations and electrical characterisation of memory device obtained from a stable cobalt complex.

A Macrocyclic Gold(I)-Biphenylene Complex: Triangular Molecular Structure with Twisted Au2 (diphosphine) Corners and Reductive Elimination of [6]Cycloparaphenylene

The digold(I) complex [Au₂ Cl₂ (Cy₂ PCH₂ PCy₂ )] reacts with 4,4'-diphenylene diboronic acid to form a triangular macrocyclic complex with twisted Au-P-C-P-Au groups at the three corners. The synthesis of the complex and its chemical oxidation produced [6]cycloparaphenylene ([6]CPP) in 59 % overall yield.

Synthesis, Photophysical, Photochromic, and Photomodulated Resistive Memory Studies of Dithienylethene-Containing Copper(I) Diimine Complexes

A series of dithienylethene-containing copper(I) diimine complexes have been synthesized and structurally characterized. Systematic studies on their photophysics, electrochemistry, and photochromism have been carried out. The photoinduced color changes of the copper(I) complexes have been achieved by photoexcitation into the metal-to-ligand charge-transfer (MLCT) absorption bands, indicating the photosensitization of light-induced cyclization by the ³MLCT excited state. In addition, by an increase in either the steric bulkiness around the copper(I) center or the structural rigidity of the complexes, the quantum efficiencies of photoluminescence and photocyclization can be effectively enhanced because of suppression of the flattening distortion of the complexes at the MLCT excited state. Furthermore, one of the complexes has been employed as an active component in the fabrication of solution-processed resistive memory devices. Notable lowering of the switching threshold voltage of the binary memory devices has been realized through photocyclization of the dithienylethene-containing copper(I) system.

Graphene Oxide: Graphene Quantum Dot Nanocomposite for Better Memristic Switching Behaviors

Tristable memristic switching provides the capability for multi-bit data storage. In this study, all-inorganic multi-bit memory devices were successfully manufactured by the attachment of graphene quantum dots (GQDs) onto graphene oxide (GO) through a solution-processable method. By means of doping GQDs as charge-trapping centers, the device indium-tin oxide (ITO)/GO:0.5 wt%GQDs/Ni revealed controllable memristic switching behaviors that were tunable from binary to ternary, and remarkably enhanced in contrast with ITO/GO/Ni. It was found that the device has an excellent performance in memristic switching parameters, with a SET1, SET2 and RESET voltage of -0.9 V, -1.7 V and 5.15 V, as well as a high ON2/ON1/OFF current ratio (103:102:1), and a long retention time (104 s) together with 100 successive cycles. The conduction mechanism of the binary and ternary GO-based memory cells was discussed in terms of experimental data employing a charge trapping-detrapping mechanism. The reinforcement effect of GQDs on the memristic switching of GO through cycle-to-cycle operation has been extensively investigated, offering great potential application for multi-bit data storage in ultrahigh-density, nonvolatile memory.

Charge disproportionate molecular redox for discrete memristive and memcapacitive switching

Electronic symmetry breaking by charge disproportionation results in multifaceted changes in the electronic, magnetic and optical properties of a material, triggering ferroelectricity, metal/insulator transition and colossal magnetoresistance. Yet, charge disproportionation lacks technological relevance because it occurs only under specific physical conditions of high or low temperature or high pressure. Here we demonstrate a voltage-triggered charge disproportionation in thin molecular films of a metal-organic complex occurring in ambient conditions. This provides a technologically relevant molecular route for simultaneous realization of a ternary memristor and a binary memcapacitor, scalable down to a device area of 60 nm². Supported by mathematical modelling, our results establish that multiple memristive states can be functionally non-volatile, yet discrete-a combination perceived as theoretically prohibited. Our device could be used as a binary or ternary memristor, a binary memcapacitor or both concomitantly, and unlike the existing 'continuous state' memristors, its discrete states are optimal for high-density, ultra-low-energy digital computing.

Chameleon Luminophore for Erasable Encrypted and Decrypted Devices: From Dual-Channel, Programmable, Smart Sensory Lanthanide Hydrogel to Logic Devices

With the rapid development of the data security technology, increasing attention has been paid to programmable memory materials with desirable security. However, most conventional memory devices only have a single switchable color state. In this research, a kind of pH-responsive Chameleon luminescent sensor (Lap@Eu-OFX, Lap = laponite, OFX = ofloxacin) based on lanthanide doping has been fabricated, which can realize highly contrast, dynamically controlled full-color display by changing the pH value of the solution. The advanced programmable security inks, including the green and red luminescent inks, have been prepared and used to protect confidential information. More interestingly, triethylamine and hydrochloric acid are selected as encryption and decryption reagents, which can repeatedly switch the emission color of important data. Hence, the high-tech security inks show great potential in data coding, multiencryption, and decryption under UV light. Furthermore, the designed dual-channel memory device, Lap@Eu-OFX@CS (CS = Chitosan), enables reversible synchronous switching of sol-gel and emission color when converting from acid to base conditions. This can be dynamically monitored by a subsequent logic gate system and can be converted and stored into binary values. This work provides an effective approach for the design and promising application of information encryptor, smart monitor, and circuit controllers.

Dual stimuli-responsive lanthanide-based phosphors for an advanced full-color anti-counterfeiting system

Dual stimuli-responsive lanthanide (Ln)-based phosphors were prepared for constructing a multi-level full color anti-counterfeiting system. The encrypted information can be visually read out under UV irradiation. Further triggered by water, not only are the fluorescence colors changed, but so are the patterns of the encrypted information. The Ln-based phosphors can be cost-effectively prepared in a simple way, presenting great potential application in constructing an advanced anti-counterfeiting system with a convenient authentication assay.

Dual stimuli-responsive lanthanide-based phosphors were prepared for constructing a multilevel full color anti-counterfeiting system, augmenting the security level for information protection.

Highly Robust Organometallic Small-Molecule-Based Nonvolatile Resistive Memory Controlled by a Redox-Gated Switching Mechanism

Although organic small-molecule-based memory devices (OSMDs) have been demonstrated to show great potential for the application in next-generation data-storage technology, progress toward their further development has been hugely hindered by the ambiguity of their electrical switching mechanism. Thus, purposely fabricating OSMDs with a definite switching behavior is very urgent. Here, we reported a redox-gated nonvolatile rewritable memory device using an organometallic small molecule as an active material. By introducing the redox-active ferrocene into an organic skeleton, the target small molecule exhibits reliable and robust FLASH-type bistable electrical characteristics with a clear redox-controlled switching mechanism, which leads to low operational voltages, good endurance, and long retention. Our study offers a proof-of-concept strategy to design controllable OSMDs with excellent performances.

Photochromic Barbiturate Pendant-Containing Benzo[b]phosphole Oxides with Co-Assembly Property and Photoinduced Morphological Changes

A series of novel barbiturate pendant-containing benzo[b]phosphole oxides has been demonstrated to exhibit photochromic and co-assembly properties. Both the open form and the photogenerated closed form of the diarylethene-based benzo[b]phosphole oxides have displayed color changes with new appearance of the bathochromic-shifted lowest-energy absorption bands upon addition of the H-bonding ditopic receptor that is complementary to the barbiturate groups, probably resulting in the formation of a supramolecular polymer. The co-assembly mixtures have displayed dissociation and association processes upon heating and cooling, respectively. Moreover, both the unassembled and co-assembled states of the benzo[b]phosphole oxide have exhibited photoinduced coloration, leading to a near-infrared absorption behavior. Multiaddressable states of the co-assembly mixture with multiple colors have been achieved via the combination of photochromism and thermochromism. More interestingly, photoinduced morphological changes from extensive porous network structures to ring-like aggregates have been observed for the co-assembly upon photoirradiation. The present work provides important insight for further developments of the multiaddressable systems and the supramolecular polymers with photo- and thermo-responsive behaviors, paving the way for the future design of photochromic materials with interesting photocontrollable functions.

Dibenzo[b,e]phosphindolizines synthesized by a ring-closing metathesis of benzo[b]phospholes with two vinyl tethers

Dibenzo[b,e]phosphindolizines 1 were successfully synthesized by a ring-closing metathesis of benzo[b]phosphole chalcogenides 2a-2c with two vinyl tethers (for chalcogen analogs 1a-1c), and by a deselenization reaction (for lone-pair analog 1d). The structures, properties, and bowl inversion derived from a phosphorus atom were fully investigated.

Ternary Memristic Effect of Trilayer-Structured Graphene-Based Memory Devices

A tristable memory device with a trilayer structure utilizes poly(methyl methacrylate) (PMMA) sandwiched between double-stacked novel nanocomposite films that consist of 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) doped with graphene oxide (GO). We successfully fabricated devices consisting of single and double GO@PBD nanocomposite films embedded in polymer layers. These devices had binary and ternary nonvolatile resistive switching behaviors, respectively. Binary memristic behaviors were observed for the device with a single GO@PBD nanocomposite film, while ternary behaviors were observed for the device with the double GO@PBD nanocomposite films. The heterostructure GO@PBD/PMMA/GO@PBD demonstrated ternary charge transport on the basis of I–V fitting curves and energy-band diagrams. Tristable memory properties could be enhanced by this novel trilayer structure. These results show that the novel graphene-based memory devices with trilayer structure can be applied to memristic devices. Charge trap materials with this innovative architecture for memristic devices offer a novel design scheme for multi-bit data storage.

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure-Property Relationships and Applications

Conjugated poly-ynes and poly(metalla-ynes) constitute an important class of new materials with potential application in various domains of science. The key factors responsible for the diverse usage of these materials is their intriguing and tunable chemical and photophysical properties. This review highlights fascinating advances made in the field of conjugated organic poly-ynes and poly(metalla-ynes) incorporating group 4-11 metals. This includes several important aspects of conjugated poly-ynes viz. synthetic protocols, bonding, electronic structure, nature of luminescence, structure-property relationships, diverse applications, and concluding remarks. Furthermore, we delineated the future directions and challenges in this particular area of research.

Amphiphilic Carbazole-Containing Compounds with Lower Critical Solution Temperature Behavior for Supramolecular Self-Assembly and Solution-Processable Resistive Memories

The self-organization and resistive memory performances of a series of newly synthesized water-soluble amphiphilic carbazole derivatives have been explored. Temperature-dependent UV/Vis absorption spectroscopy has been conducted to study the isodesmic self-assembly mechanism of the carbazole-containing compounds. This class of compounds also exhibits interesting lower critical solution temperature properties, which are sensitive to concentration and ionic additives. One of the compounds has been solution-processed and utilized as an active material in the engineering of resistive memory devices, exhibiting a switching voltage of about 3.9 V, a constant ON/OFF current ratio of 10⁶ , and a long retention time of 10⁴  s. The present work demonstrates the versatile potential applications of water-soluble amphiphilic carbazole-containing compounds in supramolecular chemistry and resistive memory devices.

Cyclometalated gold(iii) complexes: noticeable differences between (N,C) and (P,C) ligands in migratory insertion

Gold(iii) complexes are garnering increasing interest for opto-electronic, therapeutic and catalytic applications.

Gold(iii) complexes are garnering increasing interest for opto-electronic, therapeutic and catalytic applications. But so far, very little is known about the factors controlling their reactivity and the very influence of the ancillary ligand. This article reports the first comprehensive study on this topic. The reactivity of a cationic (N,C) gold(iii) complex, namely 1A, towards ethylene has been thoroughly studied and compared with that of the related (P,C) complex 1C. A cationic gold(iii) complex 5A resulting from double insertion of ethylene was selectively obtained. Complex 5A was found to be remarkably stable. It was trapped with chloride and fully characterized. In marked contrast to that observed with 1C, no β-H elimination or linear-to-branched rearrangement of the alkyl chain occurred with 1A. The energy profile for the reactions of 1A with ethylene has been comprehensively investigated computationally, and the influence of the ancillary ligand has been precisely delineated. Because nitrogen is a weaker donor than carbon (and phosphorus), the (N,C) ligand is very electronically dissymmetric, much more than the (P,C) ligand. This makes the two reactive sites at gold quite different, which noticeably influences the competition between migratory insertion and β-H elimination, and actually changes the outcome of the olefin insertion at gold. This study provides valuable insight into the influence of ancillary ligands on gold(iii) reactivity, something critical to further develop Au(iii) and Au(i)/Au(iii) catalysis.

Memristic Characteristics from Bistable to Tristable Memory with Controllable Charge Trap Carbon Nanotubes

The incorporation of the one-dimensional carbon nanomaterial carbon nanotubes (CNTs) in poly(methyl methacrylate) (PMMA) was found to successfully develop a resistive switching. It implements memristic characteristics which shift from bistable to tristable memory. The localized current pathways in the organic nanocomposite layers for each intermediate resistive state (IRS) are attributed to the trapping mechanism consistent with the fluorescent measurements. Multi-bit organic memories have attracted considerable interest, which provide an effective way to increase the memory density per unit cell area. This study will be useful for the development and tuning of multi-bit storable organic nanocomposite memory device systems.

Supramolecular Assembly of Phosphole Oxide Based Alkynylplatinum(II) 2,6-Bis(N-alkylbenzimidazol-2'-yl)pyridine Complexes-An Interplay of Hydrophobicity and Aromatic π-Surfaces

A new class of phosphole oxide based alkynylplatinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine (bzimpy) complexes were synthesized and characterized. Their self-assembly was driven by hydrophobic-hydrophobic and π-π stacking interactions. The self-assembly properties were also investigated by UV/Vis absorption spectroscopy, which revealed that the alkyl-chain length of the bzimpy moiety and the π-surface area of the alkynyl ligand have significant influence on the overall self-assembly process. The alkyl-chain length also affected the morphological structures of the aggregates, which were studied by transmission electron microscopy and scanning electron microscopy.

Fluorescent and magnetic anti-counterfeiting realized by biocompatible multifunctional silicon nanoshuttle-based security ink

Herein, we present the first example of a silicon nanoshuttle-based security ink simultaneously featuring attractive optical and magnetic properties, suitable for fluorescent and magnetic anti-counterfeiting and encryption. Significantly, the information can be dual-encrypted through multi-color fluorescence and longitudinal (T₁)/transverse (T₂) relaxation contrast by using the silicon nanoshuttle-based security ink. We further demonstrate the feasibility of this high-performance ink for practical application in banknote anti-counterfeiting.

Robust resistive memory devices using solution-processable metal-coordinated azo aromatics

Non-volatile memories will play a decisive role in the next generation of digital technology. Flash memories are currently the key player in the field, yet they fail to meet the commercial demands of scalability and endurance. Resistive memory devices, and in particular memories based on low-cost, solution-processable and chemically tunable organic materials, are promising alternatives explored by the industry. However, to date, they have been lacking the performance and mechanistic understanding required for commercial translation. Here we report a resistive memory device based on a spin-coated active layer of a transition-metal complex, which shows high reproducibility (∼350 devices), fast switching (≤30 ns), excellent endurance (∼10¹² cycles), stability (>10⁶ s) and scalability (down to ∼60 nm²). In situ Raman and ultraviolet-visible spectroscopy alongside spectroelectrochemistry and quantum chemical calculations demonstrate that the redox state of the ligands determines the switching states of the device whereas the counterions control the hysteresis. This insight may accelerate the technological deployment of organic resistive memories.

Resistive memory devices based on a triphenylamine-decorated non-precious cobalt(ii) bis-terpyridine complex

The ITO/active material/Au sandwiched devices of a cobalt(ii) bis-terpyridine complex decorated with two triphenylamine motifs display appealing flash-type resistive switching with a large ON/OFF ratio (>10³) and low operating voltages (<±3 V). In contrast, devices with the triphenylamine-appended terpyridine ligand show WORM-type memory behaviour.