Switching the memory behaviour from binary to ternary by triggering S 6 2- relaxation in polysulfide-bearing zinc-organic complex molecular memories.

The use of crystalline metal-organic complexes with definite structures as multilevel memories can enable explicit structure-property correlations, which is significant for designing the next generation of memories. Here, four Zn-polysulfide complexes with different degrees of conjugation have been fabricated as memory devices. ZnS ₆ (L) ₂ -based memories (L = pyridine and 3-methylpyridine) can exhibit only bipolar binary memory performances, but ZnS ₆ (L)-based memories (L = 2,2'-bipyridine and 1,10-phenanthroline) illustrate non-volatile ternary memory performances with high ON2/ON1/OFF ratios (10 ^4.22 /10 ^2.27 /1 and 10 ^4.85 /10 ^2.58 /1) and ternary yields (74% and 78%). Their ON1 states stem from the packing adjustments of organic ligands upon the injection of carriers, and the ON2 states are a result of the ring-to-chain relaxation of S ₆ ^2- anions. The lower conjugated degrees in ZnS ₆ (L) ₂ result in less compact packing; consequently, the adjacent S ₆ ^2- rings are too long to trigger the S ₆ ^2- relaxation. The deep structure-property correlation in this work provides a new strategy for implementing multilevel memory by triggering polysulfide relaxation based on the conjugated degree regulation of organic ligands.