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