Design and processing as ultrathin films of a sublimable Iron(II) spin crossover material exhibiting efficient and fast light-induced spin transition

TL;DR

This paper introduces a novel sublimable iron(II) spin crossover complex that retains its bistability and exhibits rapid, efficient light-induced spin transitions even in ultrathin film form, enabling potential electronic device applications.

Contribution

It reports the synthesis, characterization, and successful formation of ultrathin films of a new sublimable SCO complex that maintains its properties after processing.

Findings

The complex is thermally stable and sublimable.

Ultrathin films (15 nm) exhibit fast light-induced spin transition.

SCO properties are preserved after film formation.

Abstract

Materials based on spin crossover (SCO) molecules have centred the attention in Molecular Magnetism for more than forty years as they provide unique examples of multifunctional and stimuli-responsive materials, which can be then integrated into electronic devices to exploit their molecular bistability. This process often requires the preparation of thermally stable SCO molecules that can sublime and remain intact in contact with surfaces. However, the number of robust sublimable SCO molecules is still very scarce. Here we report a novel example of this kind. It is based on a neutral iron (II) coordination complex formulated as [FeII(neoim)2], where neoimH is the ionogenic ligand 2-(1H-imidazol-2-yl)-9-methyl-1,10-phenanthroline. In the first part a comprehensive study, which covers the synthesis and magneto-structural characterization of the [FeII(neoim)2] complex as a bulk microcrystalline material, is reported. Then, in the second part we investigate the suitability of this material to form thin films through high vacuum (HV) sublimation. Finally, the retainment of all present SCO capabilities in the bulk when the material is processed is thoroughly studied by means of X-ray absorption spectroscopy. In particular, a very efficient and fast light-induced spin transition (LIESST effect) has been observed, even for ultrathin films of 15 nm.