Switching the memory behaviour from binary to ternary by triggering S 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(L)-based memories (L = pyridine and 3-methylpyridine) can exhibit only bipolar binary memory performances, but ZnS(L)-based memories (L = 2,2'-bipyridine and 1,10-phenanthroline) illustrate non-volatile ternary memory performances with high ON2/ON1/OFF ratios (10/10/1 and 10/10/1) 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 anions. The lower conjugated degrees in ZnS(L) result in less compact packing; consequently, the adjacent S rings are too long to trigger the S 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.