Surface effects on temperature-driven spin crossover in Fe(phen)₂(NCS)₂

Despite their importance in molecular spintronics, the surface effects on spin crossover (SCO) behaviors are still poorly understood. Here, we report the impact of substrates on thermal SCO in Fe(phen)(2)(NCS)(2) (phen = 1,10-phenanthroline) deposited on metallic surfaces and monolayer two-dimensional materials. By first-principles calculations, we show that temperature-driven SCO is preserved on both hexagonal boron nitride and molybdenum disulfide (MoS2), while low-spin ground states are locked on metal surfaces, including Cu(111), Ag(111), and Au(111). On the contrary, the molecule in contact with graphene exhibits a high-spin ground state. We demonstrate that the spin transition temperature T-c depends critically on surface environments, and we correlate this effect with the modification of electronic structures and molecular vibrations upon adsorption. In particular, a sulfur vacancy in MoS2 considerably increases T-c. These findings open a way to nanoscale applications related to spin state bistability.