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

Poly(3,4-ethylenedioxythiophene)-Poly(styrenesulfonate) Interlayer Insertion Enables Organic Quaternary Memory

Herein, for the first time, quaternary resistive memory based on an organic molecule is achieved via surface engineering. A layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) was inserted between the indium tin oxide (ITO) electrode and the organic layer (squaraine, SA-Bu) to form an ITO/PEDOT-PSS/SA-Bu/Al architecture. The modified resistive random-access memory (RRAM) devices achieve quaternary memory switching with the highest yield (∼41%) to date. Surface morphology, crystallinity, and mosaicity of the deposited organic grains are greatly improved after insertion of a PEDOT-PSS interlayer, which provides better contacts at the grain boundaries as well as the electrode/active layer interface. The PEDOT-PSS interlayer also reduces the hole injection barrier from the electrode to the active layer. Thus, the threshold voltage of each switching is greatly reduced, allowing for more quaternary switching in a certain voltage window. Our results provide a simple yet powerful strategy as an alternative to molecular design to achieve organic quaternary resistive memory.

Linking ReI and PtII Chromophores with Aminopyridines: A Simple Route to Achieve a Complicated Photophysical Behavior

The bifunctional aminopyridine ligands H₂ N-(CH₂ )_n -4-C₅ H₄ N (n=0, L1; 1, L2; 2, L3) have been utilized for the preparation of the rhenium complexes [Re(phen)(CO)₃ (L1-L3)]⁺ (1-3; phen=phenanthroline). Complexes 2 and 3 with NH₂ -coordinated L2 and L3, respectively, were coupled with cycloplatinated motifs {Pt(ppy)Cl} and {Pt(dpyb)}⁺ (ppy=2-phenylpyridine, dpyb=dipyridylbenzene) to give the bimetallic species [Re(phen)(CO)₃ (μ-L2/L3)Pt(ppy)Cl]⁺ (4, 6) and [Re(phen)(CO)₃ (μ-L2/L3)Pt(dpyb)]²⁺ (5, 7). In solution, complexes 4 and 6 show ³ MLCT {Re}-based emission at 298 K, which changes to the ³ IL(ppy) state at 77 K. The photophysical properties of compounds 5 and 7 display a pronounced concentration dependence, presumably due to the formation of bimolecular aggregates. Analysis of the spectroscopic data, combined with TD-DFT simulations, suggest that unconventional heteroleptic {Re(phen)}⋅⋅⋅{Pt(dpyb)} π-π stacking operates as the driving force for ground-state association. The latter, together with intra- and intermolecular energy-transfer processes, determines the appearance of multiple emission bands and results in nonlinear relaxation kinetics of the excited states.

Smart Luminescent Coordination Polymers toward Multimode Logic Gates: Time-Resolved, Tribochromic and Excitation-Dependent Fluorescence/Phosphorescence Emission

In this work, we propose that lanthanide cations (such as Eu³⁺ and Tb³⁺)-doped long-afterglow coordination polymers (CPs) can be an effective tool for designing multimode optical logic gates based on their tunable fluorescence/phosphorescence transformation and state-dependent emission. First, multicolor and white-light luminescence across the blue/green/yellow/red visible regions can be obtained by balancing the co-doping ratio of Eu³⁺/Tb³⁺ cations and suitable excitations. Additionally, a new tribochromic Eu-Cd-CP was developed based on the mechanism of a change in structural symmetry. Benefitting from long-afterglow, tribochromism, and excitation-dependent emission on the same luminescent CP, a new three-input and three-output logic gate was obtained. Therefore, this work not only provides detailed insights into the interesting fields of tribochromism and tunable photoemission, but also confirms that long-afterglow CPs can serve as a new platform for the construction of smart luminescent systems and multimode optical logic gates.

Switching of Resistive Memory Behavior from Binary to Ternary Logic via Alteration of Substituent Positioning on the Subphthalocyanine Core

Two new axially or peripherally functionalized subphthalocyanines with the decoration of donor-acceptor substituents have been successfully synthesized, characterized and employed in the application of resistive memory device via solution-processable technique. Axially substituted subphthalocyanine shows ternary resistive memory behavior with well-separated current ratios of 1:10⁶:10⁸ between "OFF", "ON1" and "ON2" states, while only binary logic is observed for peripherally substituted subphthalocyanine. Computational studies show the presence of two well-separated charge transfer states in the axially substituted subphthalocyanine, while the charge transfer processes between the peripheral substituents and the subphthalocyanine core are found to be very close in energy. This work has demonstrated the impact of the substituent positioning on the subphthalocyanine-based memory device performance, providing a new research dimension for the future design and development of multistate organic resistive memory.

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.

A Stimuli-Responsive Smart Lanthanide Nanocomposite for Multidimensional Optical Recording and Encryption

A stimuli-responsive lanthanide-based smart nanocomposite has been fabricated by supramolecular assembly and applied as an active material in multidimensional memory materials. Conjugation of the lanthanide complexes with carbon dots provides a stimuli response that is based on the modulation of the energy level of the ligand and affords microsecond-to-nanosecond fluorescence lifetimes, giving rise to intriguing memory performance in the spatial and temporal dimension. The present study points to a new direction for the future development of multidimensional memory materials based on inorganic-organic hybrid nanosystems.

Triindole-Tris-Alkynyl-Bridged Trinuclear Gold(I) Complexes for Cooperative Supramolecular Self-Assembly and Small-Molecule Solution-Processable Resistive Memories

A novel class of luminescent trinuclear alkynylgold(I) complexes with N-alkyl substituted triindole ligands has been synthesized and characterized. They are found to exhibit rich photophysical and electrochemical properties. The complexes have been demonstrated to display interesting supramolecular assembly with spherical nanostructures in aqueous THF solution through a cooperative growth mechanism. The self-assembly process is shown to be mediated by the π-π stacking interactions and hydrophobic-hydrophobic interactions of the triindole moieties upon solvent modulation. These gold(I) complexes have been employed as active materials in the fabrication of solution-processable resistive memory devices, showing promising binary memory performances with low switching threshold voltages of ca. 1.5 V, high ON/OFF current ratio of up to 10⁵, long retention time of over 10⁴ s, and excellent stability. The present work opens up a new avenue for the future design of versatile organogold(I) complexes that could serve as multifunctional materials.

Luminescent closed shell nickel(ii) pyridyl-azo-oximates and the open shell anion radical congener: molecular and electronic structure, ligand redox behaviour and biological activity

Luminescent nickel(ii) complexes have been synthesized using redox-active azo-oximes. The superior π-acidity of the organic backbone is a key to the isolation of Ni(ii) anion radicals.

Synthesis of new conjugated polymers with coordinated praseodymium complexes for polymer memory devices

A series of novel praseodymium(Pr)-coordinated polymers with phthalimide moieties were synthesized. The effects of the phthalimide moiety and neutral Pr complex on the polymer memory device performance were investigated.

Surface engineering to achieve organic ternary memory with a high device yield and improved performance

Organic memories fabricated on surface-engineered indium tin oxide show the highest ternary yield (82%) to date and better performance.

Squaraine molecules deposited on indium tin oxide (ITO) substrates modified with phosphonic acids crystalize more orderly than do those on untreated ITO. The as-fabricated electro-resistive memories show the highest ternary device yield observed to date (82%), a narrower switching voltage distribution, and better retention as well as resistance uniformity.

Evaluation of bis-cyclometalated alkynylgold(iii) sensitizers for water photoreduction to hydrogen

Gold(iii) acetylide complexes actively catalyzed the light-driven evolution of hydrogen in water when using [Co(2,2′-bipyridine)₃]Cl₂ or [Rh(4,4′-di-tert-butyl-2,2′-bipyridine)₃](PF₆)₃ as a H₂-evolved catalyst.