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

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(H₂B(pz)₂)₂(bpy)] (pz = pyrazole, bpy = 2,2′-bipyridine) with a dodecyl (C₁₂) alkyl chain yields a classical amphiphile-like functional and vacuum-sublimable charge-neutral Fe^II complex, [Fe(H₂B(pz)₂)₂(C₁₂-bpy)] (C₁₂-bpy = dodecyl[2,2′-bipyridine]-5-carboxylate). Both the bulk powder and 10 nm thin films sublimed onto either quartz glass or SiO_x 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.

Self-assembly and spin crossover go hand in hand, leading to the realization of comparable spin-state switching characteristics of a pseudoamphiphilic charge-neutral and vacuum-sublimable functional SCO complex in bulk and thin film states with implications for the development of large-area spintronics devices based on SCO complexes.

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