Spin controlled transport switching with negative differential resistance in a chiral molecular device

Manipulating electron transport through spin control is fundamental to molecular spintronics. We show that adjusting the crystal field and oxidation state of a magnetic center embedded in a chiral framework allows accurate regulation of transport across spin states ranging from S = 0 to 2. Our results reveal pronounced current drops (up to 70%) during spin transitions and the appearance of negative differential resistance (NDR), arising from bias-driven realignment of the highest occupied molecular orbitals and accompanying shifts in the transmission spectrum. We further show that asymmetric coupling to the environment, in particular through a CO axial ligand, leads to current rectification and robust NDR under reverse bias. In addition, Fe(III) junctions exhibit remarkable spin-filtering capabilities, with the S = 3/2 state achieving a spin polarization exceeding 0.95 at low bias, highlighting a versatile strategy for molecular spin-state engineering.