(bipy) Complex Through Gold Electrodes: An Ab Initio Study*

Spin-crossover (SCO) molecules coupled to electrodes show promise as possible spintronic devices because the conductance changes with spin state. Prior ab initio transport studies find, however, that different configurations of the electrode can lead to different predictions, most likely due to the coupling of the electrodes with the molecular complex.^[1] To address this, we investigate the impact on ab initio non-equilibrium Green’s function transport calculations by isolating an Fe(II) complex Fe[H₂B(Pz)₂]₂(bipy) placed between two Au(111) electrodes by inserting graphene supports between the lead and the SCO molecule. We find that the interplay between the graphene and the SCO molecule orbitals provides transport channels within a small bias window, effectively removing the direct coupling of the electrode to the SCO molecule. These channels show different transmission profiles above and below the Fermi energy depending on whether the molecule is in the high spin (S=2) state or the low spin (S=0) state. We calculate a relatively large rise in the current for the high spin state at small bias (V = 0.1 eV), which is not seen in the low spin state, leading to a high current on/off ratio.

[1] D. Li, et al., J. Phys. Chem. Lett., 2022, 13, 7514. DOI: 10.1021/acs.jpclett.2c01934