Asymmetrically Functionalized Phenanthro[9,10-d]imidazole-Based Donor–Acceptor Architectures for High-Performance Ternary Memory Devices

A series of asymmetric D-A-D′- and D-A-A′-based compounds with phenanthroimidazole and triphenylamine were designed and synthesized for multilevel data storage. Different donors/acceptors in the D–A architecture influence the compound’s photophysical, electrochemical, and memory performance. The photophysical investigations confirm an efficient intramolecular charge transfer (ICT) range of 330–350 nm, and the electrochemical studies showed an irreversible anodic peak (1.01–1.06 V) with a narrow bandgap of 3.54–3.71 eV. The D-A-D′-based compounds with electron-donating substituents exhibited binary write-once-read-many (WORM) memory behavior with a long retention time (4 × 103 s) and good stability over 100 cycles. The pyrene-substituted compound showed a maximum ON/OFF current ratio of 107, with a low threshold voltage of −1.02 V. Notably, the compounds with electron-withdrawing groups displayed ternary WORM memory behavior due to the two distinct charge traps in the D-A-A′ system. The devices exhibited an ON/OFF current ratio of 1 × 105, with a threshold voltage of −1.20 V. The molecular simulations confirm the charge transfer and charge traps in the compounds, which signifies the underlying mechanism for these memory devices. This study has demonstrated the influence of different substituents on memory switching from binary to ternary. It provides insight into high-density data storage devices’ future design and development.