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

Light-Induced Spin Crossover in an Fe(II) Low-Spin Complex Enabled by Surface Adsorption

“…This leads to characteristic and distinct X-ray absorption (XA) spectra for the HS and LS states as previously reported for Fe 2+ -based SCO compounds. 17,29,[52][53][54][55] Figure 2a shows an XA spectrum at the Fe L 3 and L 2 edges for Fe-pypyr powder at 120 K (blue curve). As expected for a nominal LS compound, the XA spectrum is typical of that of a pure LS state.…”

Linking Electronic Transport through a Spin Crossover Thin Film to the Molecular Spin State Using X-ray Absorption Spectroscopy Operando Techniques

“…Impact at T = 300 K of sweeping photon energy across the Fe L 3 edge on a) X-ray absorption spectra measured on the 300x50 m 2 Au/[Fe(H 2 B(pz) 2 ) 2 (NH 2 -phen)]/Au junction in TFY mode with a 800x600 m 2 X-ray beam, and on b) the current flowing across the device for both signs of 10mV applied bias, i.e in a device-centric operando approach11 . The HS state witnessed in the TFY spectrum of panel (a) corroborates data for the thick SCO reference film ofFig.…”

Amine‐Functionalized Spin Crossover Building Blocks

“…by temperature, pressure or light . This translates into potential applicability for room temperature‐operable molecular electronics, sensors and displays, which prompted extensive studies on multiple families of SCO complexes . Given the pronounced sensitivity of most SCO compounds to minute changes in structure and environment, a key challenge remains: the functionalization of complexes enabling their facile integration via covalent links in a variety of materials relevant to the respective application while retaining their SCO characteristics .…”