Chains of Spin-Crossover Complexes Synthesized on the Ag(111) Surface

Artificial spin chains composed of switchable units are a key objective in molecular spintronics, but their creation on surfaces is a challenge. Spin-crossover molecules allow for the reversible switching between spin states and could provide a means of creating such functional nanostructures through on-surface synthesis. We report the first on-surface thermally activated Ullmann coupling of spin-crossover complexes on a Ag(111) surface. Using scanning tunneling microscopy, we demonstrated the formation of molecular chains with electrically tunable spin states. The conductance spectra of individual molecules in chains exhibit spin-flip excitations. A comparison to a Heisenberg spin chain shows that the spins are antiferromagnetically coupled. Reversible manipulation of the molecules in the chains suppresses the spin excitations, indicating a transition from high spin to low spin S = 0. Overall, these observations confirm that Ullmann coupling on surfaces is a viable strategy for engineering electrically programmable spin chains with a spin-crossover functionality.