Spin state manipulation of a spiropyran (SP) and Dy complex with SP ligand molecules on Au(111) by scanning tunneling microscopy

We examine the isomerization and variation of the spin state of molecules adsorbed on the Au(111) surface by injecting tunneling electrons. We employed molecules of spiropyran (SP) and a SP-based Dy complex with the hexa-fluoro-acetylacetonate (hfac) ligand and DyN3O5 coordination, SP-DyL(hfac)2. SP molecules, transferred by vacuum sublimation, form an ordered lattice. Injection of tunneling electrons changes the conformation of the SP molecule, which can be accounted for by isomerization into a merocyanine (MC) molecule. The change of the magnetic property is confirmed by detecting the Kondo resonance, which is a high-density of states at the Fermi level by forming the spin-singlet in the neighbor of the spin impurity The appearance of the Kondo resonance is detected only in the converted MC molecule, which originated from the MC molecule's pi radicals. Injection of tunneling electrons can cause similar isomerization for the SP-DyL(hfac)2 molecule. The appearance of the magnetic moment is detected after the conversion by Kondo resonance, which suggests the formation of MC-DyL(hfac)2. Density functional theory calculations support experimental observations. Since the MC-DyL(hfac)2 molecule's single-molecule magnet nature was confirmed previously, the observations in this study might pave the way for designing and developing single-molecule magnets based on photoisomerization. The tunneling electrons triggered conformational changes of SP to MC and SP-DyL(hfac)2 to MC-DyL(hfac)2 were successfully implemented with tunneling electrons injection.