The incorporation of the ionization effect in organic semiconductors assists in triggering multilevel resistive memory behaviors

The introduction of the ionization effect into organic small molecules could be a promising strategy for modulating their memory behaviors. Herein, two new ionic and zwitterionic D/A-conjugated small molecules (LD-IOM and LD-ZIOM) have been prepared via salification and further zwitterionization from their neutral parent structure LD, a pyridine-based molecule. Incredible blue-shifting absorptions of LD-IOM and LD-ZIOM by 44 and 88 nm, respectively, were observed as compared with LD. Molecular dynamics simulations suggest the preferential molecular packing modes of J-, Slide-H- and H-aggregations for LD, LD-IOM and LD-ZIOM, which are in good agreement with the experimental results. LD-based memory devices exhibited binary WORM-type memory performance with the probability for minor misreading, while LD-IOM and LD-ZIOM-based devices revealed upgraded ternary memory behaviors. The counterions in LD-IOM manifested an induction effect on the molecular packing orientations and caused two separate threshold voltage distributions, attributed to ion fractionation and the migration effect.