Switching the memory behaviour from binary to ternary by triggering S62− relaxation in polysulfide-bearing zinc–organic complex molecular memories

Abstract

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. ZnS₆(L)₂-based memories (L = pyridine and 3-methylpyridine) can exhibit only bipolar binary memory performances, but ZnS₆(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 S₆²⁻ anions. The lower conjugated degrees in ZnS₆(L)₂ result in less compact packing; consequently, the adjacent S₆²⁻ rings are too long to trigger the S₆²⁻ 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.