Engineering on-surface spin crossover: spin-state switching in a self-assembled film of vacuum-sublimable functional molecule

Abstract

Realization of spin crossover (SCO) based applications requires studying of\nspin state switching characteristics of SCO complex molecules at nanostructured\nenvironments especially on-surface. Except for a very few cases, the SCO of a\nsurface bound thin molecular film is either quenched or heavily altered due to\n(i) strong molecule-surface interactions and (ii) differing intermolecular\ninteractions in films relative to the bulk. By fabricating SCO complexes on a\nweakly interacting surface such as highly oriented pyrolytic graphite (HOPG)\nand copper nitride (CuN), the interfacial quenching problem has been tackled.\nHowever, engineering intermolecular interactions in thin SCO active films is\nrather difficult. This work proposes a molecular self-assembly strategy to\nfabricate thin spin switchable surface bound films with programmable\nintermolecular interactions. Molecular engineering of the parent complex system\n[Fe(H$_{2}$B(pz)$_{2}$)$_{2}$(bpy)] (pz = pyrazole, bpy = 2,2'-bipyridine) with\na dodecyl (C$_{12}$) alkyl chain yielded a classical amphiphile-like functional\nand vacuum sublimable charge neutral Fe$^{\\rm II}$ complex,\n[Fe(H$_{2}$B(pz)$_{2}$)$_{2}$(C$_{12}$-bpy)] (C$_{12}$-bpy =\ndodecyl[2,2'-bipyridine]-5-carboxylate). The bulk powder and 10 nm thin film,\non quartz glass/SiO$_{\\rm x}$ surface, of the complex showed comparable spin\nstate switching characteristics mediated by similar lamellar bilayer like\nself-assembly/molecular interactions in both bulk and thin film states. This\nunprecedented observation augurs well for the development of SCO based\napplications, especially in molecular spintronics.\n