Coordination structure conversion of protonated bisporphyrinato terbium( iii ) double-decker complexes and creation of a Kondo assembly by electron injection on the Au(111) surface

The first step towards the synthesis of single-molecule magnet (SMM)-based spintronics devices is the organization and manipulation of magnetic molecules on surfaces. Our previous studies on bulk crystals demonstrated that protonated porphyrinato double-decker complexes [Tb(Hoep)(oep)] (oep = 2,3,7,8,12,13,17,18-octaethylporphyrinato) are not SMMs; however, once a hydrogen is removed to produce their neutral radical forms, [Tb(oep)₂], they convert to SMMs. These intriguing properties encouraged us to examine the electronic/spin properties of these complexes and their chemical conversion ability after their transfer onto a metal substrate, similar to the environment required for the practical application of SMMs. Herein, we conducted a single-molecule-scale conversion of the protonated bis(porphyrinato)terbium(iii) double-decker complex [Tb(Hoep)(oep)], whose hepta-coordinated terbium ion changes into octa-coordinated [Tb(oep)₂] on detaching a hydrogen atom by scanning tunnelling microscopy. This conversion can be caused by the injection of tunnelling electrons of energy 1.5-2.5 eV. We confirmed the conversion by analysing the topographic image and the spin state of the molecule. The latter was achieved by examining the Kondo resonance, which originated from the screening of the molecular spin by the conduction electrons of the metal. The Kondo resonance was not observed for [Tb(Hoep)(oep)] but was observed for the converted species, which agrees well with a model containing the [Tb(oep)₂] molecule and Kondo resonance originating from the π-electron spin of the porphyrin ligand. Even though it is not possible to provide complete evidence of the SMM properties of the transferred molecule, we have demonstrated a possible path to realize the switch-on SMM properties of a single molecule.