Surface Stabilization to Enhance Single Molecule Toroidal Behavior in {Dy3} Molecules: the Impact of Au(111), MgO, and Graphene Surfaces

Single-molecule toroids (SMTs), with vortex-like magnetic anisotropy axes, hold promise for quantum technologies, but controlling their toroidal states on the surface remains challenging. To address this, the SMT behavior of [Dy3(mu 3-OH)2L3Cl(H2O)5]Cl3 (where L = ortho-vanillin) grafted onto Au(111), MgO has been studied, and graphene surfaces in pristine form (1) and with pyrene (2) and (CH2)8S (3) linkers, using periodic density functional theory and ab initio CASSCF/RASSI-SO methods. Both pristine and chemically functionalized molecules are stable on Au(111) and graphene surfaces; however, functionalization provides higher binding energies and, in some cases, enhances the SMT properties. The MgO surface, however, is found to be unsuitable as it abstracts an H atom from the molecule, leading to the loss of its SMT characteristics. The energy gap (Delta E) between the toroidal (nonmagnetic) and spin-flip (magnetic) states in complex 1 on Au(111) and graphene surfaces are 6.9 and 6.6 cm-1, respectively. Complexes 2 on Au(111) and 3 on graphene exhibit Delta E and toroidal blocking fields of 9.8 cm-1/1.2 T and 6.8 cm-1/0.83 T, respectively, representing the highest recorded values for this class of SMTs. These findings demonstrate the potential of surface stabilization to improve the functionality and applicability of SMTs in advanced quantum technologies.