Study of Electronic and Steric Effects of Different Substituents in Donor–Acceptor Molecules on Multilevel Organic Memory Data Storage Performance

To study the influence of different types of substituent moieties onto the molecular backbones of conjugated donor–acceptor (D–A) molecules on the thin-film morphology and performance of their memory devices, three new molecules X-TBT were synthesized, which consist of the same backbone of two triphenylamine (T) groups and benzothiadiazole (BT) group, but have different substituents (X) with different electronic effects, that is, cyano group (CN), tert-butyl group (^tBu), and methoxy group (OMe). Nonvolatile ternary write-once-read-many-times (WORM) data storage behavior is achieved for the CN-TBT and ^tBu-TBT based devices as compared to the binary memory characteristic of TBT (X = H). In contrast, OMe-TBT based device still maintains binary WORM behavior due to its unfavorable molecular packing motif and weak intermolecular charge transfer effect, but exhibits the lowest operating voltage (1.4 V) as a result of the lowest energy barrier between electrode and active layer. Notably, the ^tBu-TBT based device displays the highest I_ON2/I_ON1/I_OFF ratio of 10⁷:10³:1. Altering the substituents in D–A molecules can adjust the molecular packing, thin film morphology, and electron trap depth of the active layer, which then significantly influence the memory performance.