Implementation of Thermal-Triggered Binary–Ternary Switchable Memory Performance in Zn/polysulfide/organic Complex-Based Memorizers by Finely Modulating the S62– Relaxation

Polysulfide-based multilevel memorizers are promising as novel memorizers, in which the occurrence of Sn2– relaxation is key for their multilevel memory. However, the effects of crystal packing and the side group of organic ligands on Sn2– relaxation are still ambiguous. In this work, ionic [Zn(S6)2·Zn2(Bipy)2SO4 (1), Zn(S6)2·Zn(Pmbipy)3 (2)] and neutral [ZnS6(Ombipy) (3), ZnS6(Phen)2 (4)] Zn/polysulfide/organic complexes with different packing modes and structures of organic ligands have been synthesized and were fabricated as memory devices. In both ionic and neutral Zn complexes, the S62– relaxation will be blocked by steric hindrances due to the packing of counter-cations and hydrogen-bond restrictions. Consequently, only the binary memory performances can be seen in FTO/1/Ag, FTO/2/Ag, and FTO/4/Ag, which originate from the more condensed packing of conjugated ligands upon electrical stimulus. Interestingly, FTO/3/Ag illustrates the unique thermally triggered reversible binary–ternary switchable memory performance. In detail, after introducing a methyl group on the 6′-position of bipyridine in ZnS6(Ombipy) (3), the ring-to-chain relaxation of S62– anions at room temperature will be inhibited, but it can happen at a higher temperature of 120 °C, which has been verified by elongated S–S lengths and the strengthened C–H···S hydrogen bond upon heating. The rules drawn in this work will provide a useful guide for the design of stimulus-responsive memorizers that can be applied in special industries such as automobile, oil, and gas industries.