Single-Molecule Spin Switch Based on Voltage-Triggered Distortion of the Coordination Sphere

Here, we report on a new single-molecule-switching concept based on the coordination-sphere-dependent spin state of FeII species. The perpendicular arrangement of two terpyridine (tpy) ligands within heteroleptic complexes is distorted by the applied electric field. Whereas one ligand fixes the complex in the junction, the second one exhibits an intrinsic dipole moment which senses the E field and causes the distortion of the FeII coordination sphere triggering the alteration of its spin state. A series of complexes with different dipole moments have been synthesized and their transport features were investigated via mechanically controlled break-junctions. Statistical analyses support the hypothesized switching mechanism with increasing numbers of junctions displaying voltage-dependent bistabilities upon increasing the FeII complexes' intrinsic dipole moments. A constant threshold value of the E field required for switching corroborates the mechanism.