Exploring the Transformation of Static Random Access Memory to Write-Once-Read-Many-Times Memory Behavior in Imidazole–Triphenylamine-Based Devices

A series of D–A, A–D–D, and A–D–A-based compounds with imidazole and triphenylamine were designed and synthesized to study the memristor performance. The D–A system was functionalized with different substitutions (phenyl, anthracene, and indoloquinoxaline) in the terminal position of triarylamine to alter the coplanarity and conjugation length. The electrochemical investigations showed an irreversible anodic peak (1.01–1.25 V) with a band gap of 2.72–3.05 eV, and the photophysical studies revealed the intramolecular charge transfer. The compound with simple imidazole and triphenylamine exhibited static random access memory (SRAM) behavior due to the coplanar structure back charge transfer (CT). Besides, the A–D–D-based system with an anthracene substituent displayed the binary write-once-read-many-times (WORM) memory with the ON/OFF current ratio of 104. The indoloquinoxaline-substituted compound notably showed a ternary WORM memory due to two different charge-trapping centers in the A–D–A system. The devices with end-capped triphenylamine exhibited a long-lasting retention time (2 × 103) and endurance cycles. The molecular simulations unveiled the underlying mechanism for the conversion from SRAM to WORM via altering the dihedral angle by different substituents. Moreover, the compounds CT and charge trap support the binary and ternary WORM-based memory devices. This work demonstrates the strategy to convert the SRAM into WORM memory behavior by preventing the back CT from an excited state to the ground state.