On-surface coupling of spin-crossover molecules - scanning tunneling microscopy investigations

• Applicants: Professor Dr. Richard Berndt; Professor Dr. Felix Tuczek
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas ; Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560789750

New vacuum-evaporable Fe(II) spin-crossover complexes supported by linear tridentate ligands with halogen substituents are developed for on-surface Ullmann coupling. Analogous complexes supported by hexadentate ligands with halogen substituents are also synthesised. Increased stability of the latter systems with respect to their analogues with bis(tridentate) ligation is achieved by strapping the two tridentate subunits with a propylene or biphenyl spacer. Finally, similar systems with ethinyl substituents instead of halogen substituents are prepared for on-surface Glaser coupling. All these systems are used to generate arrays of spin-switchable Fe(II) centres on surfaces (noble metals, lead). The complexes are first deposited on these surfaces by vacuum evaporation and then coupled by Ullmann or Glaser coupling. Insight into the spin states of the individual molecules (before coupling) and the individual spin centres within the arrays formed by surface coupling is obtained by scanning tunneling microscopy and spectroscopy using relatively direct probes. These include spectroscopy of spin excitations and Yu-Shiba-Rusinov resonances. Switching will be induced by electron current and by controlling the molecular environment. In this context, the extent to which switching of a particular molecule in an array can be achieved "remotely" by manipulating neighbouring molecules will be explored. The work will address some of the core issues of SPP2491, such as electron-induced switching, interactions with neighbouring switches in a configurable matrix and with surfaces, and understanding switching mechanisms at the level of single molecules.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2491: Interactive Spin-State Switching
• Co-Investigator: Dr. Alexander Weismann