Engineering On-Surface Spin Crossover: Spin-State Switching in a Self-Assembled Film of Vacuum-Sublimable Functional Molecule.

Kumar, Kuppusamy Senthil; Studniarek, Michał; Heinrich, Benoît; Arabski, Jacek; Schmerber, Guy; Bowen, Martin; Boukari, Samy; Beaurepaire, Eric et al. · Adv Mater · 2018

basic_science · Level V

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Abstract

The realization of spin-crossover (SCO)-based applications requires study of the spin-state switching characteristics of SCO complex molecules within nanostructured environments, especially on surfaces. Except for a very few cases, the SCO of a surface-bound thin molecular film is either quenched or heavily altered due to: (i) molecule-surface interactions and (ii) differing intermolecular interactions in films relative to the bulk. By fabricating SCO complexes on a weakly interacting surface, the interfacial quenching problem is tackled. However, engineering intermolecular interactions in thin SCO active films is rather difficult. Here, a molecular self-assembly strategy is proposed to fabricate thin spin-switchable surface-bound films with programmable intermolecular interactions. Molecular engineering of the parent complex system [Fe(H<sub>2</sub> B(pz)<sub>2</sub> )<sub>2</sub> (bpy)] (pz = pyrazole, bpy = 2,2'-bipyridine) with a dodecyl (C<sub>12</sub> ) alkyl chain yields a classical amphiphile-like functional and vacuum-sublimable charge-neutral Fe<sup>II</sup> complex, [Fe(H<sub>2</sub> B(pz)<sub>2</sub> )<sub>2</sub> (C<sub>12</sub> -bpy)] (C<sub>12</sub> -bpy = dodecyl[2,2'-bipyridine]-5-carboxylate). Both the bulk powder and 10 nm thin films sublimed onto either quartz glass or SiO<sub>x</sub> surfaces of the complex show comparable spin-state switching characteristics mediated by similar lamellar bilayer like self-assembly/molecular interactions. This unprecedented observation augurs well for the development of SCO-based applications, especially in molecular spintronics.