Molecularly Engineered Ferrocene-Indolo[2,3-b]Quinoxaline D-π-A-D'/A' Systems for Non-Volatile WORM Memory Device Application

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 10²-10⁴, 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 (∼10⁴). 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.