Samuthira Nagarajan

The development of efficient and scalable organic memory devices requires molecular systems with tunable electronic properties and stable switching behavior. Herein, we report a series of redox‐active donor‐π‐acceptor‐donor/acceptor (D‐π‐A‐D′/A′) molecules incorporating ferrocene as an electron‐rich donor and indoloquinoxaline as the acceptor, connected through a conjugated phenylethynyl bridge. The electronic properties were systematically tuned by introducing various donor substituents (triphenylamine, dibenzothiophene, dibenzofuran) and an acceptor substituent (quinoline). Spectroscopic, electrochemical, and computational studies reveal efficient intramolecular charge transfer from ferrocene to the acceptor unit, with reversible Fe(II)/Fe(III) redox behavior. All compounds exhibit reliable non‐volatile resistive switching with ON/OFF ratios of 10 ² –10 ⁴ , good endurance (> 100 cycles), and retention times exceeding 4000s. Among the investigated compounds, the triphenylamine‐substituted derivative exhibited the best memory performance, delivering a lower threshold voltage of ‐1.04 V and a higher ON/OFF current ratio (∼10 ⁴ ). This improvement can be attributed to the stronger electron‐donating nature of triphenylamine, which promotes more efficient donor‐acceptor electronic communication. Density functional theory calculations further support the experimental observations, revealing that enhanced intramolecular charge transfer together with the redox‐active ferrocene unit plays a key role in the resistive switching process. These results demonstrate a promising strategy for designing high‐performance organic memory materials.

A series of ferrocene-based D–π–A-A/D′ molecules was designed and synthesized, exhibiting efficient charge transfer, low-voltage non-volatile resistive switching, high ON/OFF ratios (10 ² –10 ⁵ ), and excellent stability.

A series of pyrazole-functionalized quinolines with donor–acceptor (D–A) and donor–acceptor–donor (D–A–D) architectures was synthesized for application in multilevel organic memory devices. The donor substituents, such as tert-butyl and methoxyphenyl groups, as well as the functionalization of the pyrazole moiety on the quinoline, enable the transition from binary to ternary and quaternary memory states, thereby enhancing charge storage density. Notably, quaternary memory devices, which are rarely reported, have three ON states and one OFF state, enabling multilevel data storage and allowing two bits to be stored in a single memory cell. These devices exhibit low threshold voltages of –0.58 to –3.09 V and ON/OFF ratios of 102 to 105, thereby improving memory device performance. Photophysical and electrochemical analyses indicate enhanced charge-transfer capabilities, as evidenced by a red shift in the absorption spectra and reduced band gaps (3.02–3.15 eV). All compounds demonstrated nonvolatile write-once-read-many memory behavior, in which charge transport is primarily influenced by intramolecular charge transfer and trap-controlled space-charge-limited current mechanisms. The devices also exhibited significant stability over 100 reading cycles and 2000 s under constant stress at 0.5 V. The observed memory performance is strongly correlated with molecular structure, showing that the nature of the donor substituents and molecular architecture influence charge-transfer efficiency, trap distribution, and, ultimately, multilevel memory performance. These findings represent a significant advancement in the development of organic high-density storage memory devices.

The effect of terminal substituents on resistive memory characteristics was studied in a series of Donor‐π‐Acceptor/Donor (D‐π‐A/D) molecules with fluorene as the core donor, incorporating different terminal substitutions using a styryl π‐spacer, which were synthesized via Knoevenagel condensation followed by Suzuki cross‐coupling. The photophysical and electrochemical studies showed that all the synthesized compounds have a narrow band gap of 3.02–3.09 eV and irreversible oxidation peaks. All the memory devices fabricated from these compounds exhibited non‐volatile binary Write‐Once‐Read‐Many ( WORM) memory characteristics, with an I _ON /I _OFF ratio of 10 ³ , and the trifluoromethyl terminal group exhibited a lower threshold voltage of −1.34 V under negative bias. All the fabricated devices showed improved reliability and cell‐to‐cell reproducibility, as evidenced by statistical analyses of threshold voltages and ON/OFF current ratios. Density Functional Theory (DFT) calculations and electrostatic potential analysis support a combined charge‐transfer and charge‐trapping resistive memory mechanism, consistent with the experimental data. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) analyses confirm good film coverage and moderate roughness. Thus, the potential of the terminal substitution strategy in the D‐π‐A/D system with fluorene as the core donor has unlocked the development of efficient, solution‐processable resistive memory devices for data storage.

The ever‐increasing demand for data storage and efficient electronics has driven researchers to explore novel materials beyond traditional silicon‐based semiconductors. The distinct structure‐dependent properties of small organic molecules made them versatile materials for memory storage applications. Herein, we present quinoxaline‐based donor‐acceptor (D‐A)architected small organic molecules for nonvolatile, write‐once, read‐many (WORM) resistive‐switching memory applications. The molecule of interest, with quinoxaline as the electron acceptor and triphenylamine (TPA) and dibenzofuran as the electron donors, exhibited a significant ON/OFF ratio in the range of 10 ² –10 ^5, with the lowest threshold voltage being −0.62 V. The longer retention time of 2000 s and endurance of up to 100 cycles reveal the stability of the fabricated devices. The photo‐physical and electro‐analytical techniques revealed that the synthesized compounds possessed an ideal band gap of 2.53 to 3.03 eV, which ensures effective charge carrier transfer from HOMO to LUMO levels. These factors, along with thin‐film morphological studies, suggest that the compounds are viable as potential resistive memory devices. This study thus demonstrates that the fine‐tweaked quinoxalines are potent and versatile small organic molecules for high‐density data storage.

A series of novel donor‐bridge‐acceptor (D‐π‐A) organic small molecules featuring pyridine‐functionalized cores was designed, synthesized, and systematically investigated for application in nonvolatile resistive switching memory devices. The molecular framework was tailored via Pd‐catalyzed Suzuki cross‐coupling and Wittig–Horner condensation to integrate diverse electron‐donating and electron‐withdrawing functionalities. The molecular architecture integrated electron‐rich units, such as tert‐butylphenyl, methoxyphenyl, and dibenzofuran, with strong acceptors, such as cyano and nitroaryl groups, enable fine‐tuning of electronic properties through structural asymmetry. Photophysical studies confirmed strong intramolecular charge transfer (ICT), and electrochemical analysis revealed narrow optical bandgaps of 3.10–3.20 eV. All materials exhibited stable binary memory behavior, with ON/OFF current ratios and retention times exceeding 10 ³ s. Notably, the dibenzofuran‐nitrophenyl derivative exhibited superior performance, with a low threshold voltage of −1.11 V and an ON/OFF ratio of 10 ⁵ . Density functional theory (DFT) and electrostatic potential analyses supported a charge transfer‐assisted, charge trapping‐enabled resistive‐switching mechanism. Thin‐film morphology and GI‐XRD studies further indicated uniform film coverage and crystalline ordering. The tunable donor–acceptor substitution strategy provides valuable insights into molecular design principles for solution‐processable, high‐performance organic memory devices.

This study explores the influence of aromatic π-extension on the resistive memory performance of phenathroimidazole-based D–A compounds, with anthracene derivative showing superior performance (ON/OFF current ratio ∼10 ⁶ ).