Asymmetrically Functionalized\nPhenanthro[9,10-d]imidazole-Based\nDonor–Acceptor Architectures for High-Performance Ternary Memory\nDevices

A series\nof asymmetric D-A-D′- and D-A-A′-based compounds\nwith phenanthroimidazole and triphenylamine were designed and synthesized\nfor multilevel data storage. Different donors/acceptors in the D–A\narchitecture influence the compound’s photophysical, electrochemical,\nand memory performance. The photophysical investigations confirm an\nefficient intramolecular charge transfer (ICT) range of 330–350\nnm, and the electrochemical studies showed an irreversible anodic\npeak (1.01–1.06 V) with a narrow bandgap of 3.54–3.71\neV. The D-A-D′-based compounds with electron-donating substituents\nexhibited binary write-once-read-many (WORM) memory behavior with\na long retention time (4 × 10<sup>3</sup> s) and good stability\nover 100 cycles. The pyrene-substituted compound showed a maximum\nON/OFF current ratio of 10<sup>7</sup>, with a low threshold voltage\nof −1.02 V. Notably, the compounds with electron-withdrawing\ngroups displayed ternary WORM memory behavior due to the two distinct\ncharge traps in the D-A-A′ system. The devices exhibited an\nON/OFF current ratio of 1 × 10<sup>5</sup>, with a threshold\nvoltage of −1.20 V. The molecular simulations confirm the charge\ntransfer and charge traps in the compounds, which signifies the underlying\nmechanism for these memory devices. This study has demonstrated the\ninfluence of different substituents on memory switching from binary\nto ternary. It provides insight into high-density data storage devices’\nfuture design and development.