Exploring the influence of acceptor-strength in alkoxyphenanthrene-based A–π–D–π–A versus D–π–A architectures for resistive WORM memory devices

Abstract

In the proliferation of resistive memory devices, organic small molecules play a vital role in high-density data storage technology. Effective tuning of organic molecules through strategic design enhances their memory characteristics. Herein, we present the first systematic investigation comparing symmetric A–π–D–π–A versus D–π–A-architected compounds, revealing fundamental structure–property relationships that govern the performance of memory devices. We synthesized a series of novel compounds featuring alkoxyphenanthrene as a central core donor moiety and an ethynyl spacer linking it with indoloquinoxaline/dibenzo[a,c]phenazine as the acceptor unit. All the synthesized compounds exhibited potent binary non-volatile WORM memory behavior with ON/OFF current ratios ranging from 10³ to 10⁴, long retention times of 2 × 10³ s, and endurance characteristics of 100 cycles. Among the synthesized compounds, the A–π–D–π–A system attained a reduced threshold voltage of around −1.0 V over the other due to a well-balanced donor–acceptor system, leading to effective orbital overlap and charge distribution, a critical advancement over the D–π–A architecture device. The outperformance of the A–π–D–π–A systems was supported by the intramolecular charge transfer interactions and reduced energy band gap values observed in photophysical and electrochemical studies. The molecular simulations validated the efficient intramolecular charge transfer, which provides distinctive conductive states in the fabricated device, reinforcing the experimental observations. Thus, these insights suggest that the increase in acceptor strength in the system balances the push–pull interactions, aiming for a promising candidate for memory device applications.