Spin crossover in soft matter

Abstract

This review article is devoted to the study of the spin crossover phenomenon in soft matter. Spin crossover compounds, though known for decades, bear the potential for practical applications in switching, sensing and display devices. Having arrived at a reasonable understanding of the spin transition process in solid and liquid states, one trend in this research field is to extend the knowledge into soft matter. The review begins with a brief description of Langmuir–Blodgett thin films based on FeII coordination compounds since it represents the first study of the spin crossover phenomenon in soft matter. The following section illustrates the FeII, FeIII and CoII complexes reported so far and the interplay-synergy observed between the spin crossover or valence tautomerism phenomenon and the crystal–liquid crystal or crystal–liquid phase transitions. The spin crossover phenomenon in gels is subject of another chapter, where it is described the development of thermochromic gels making use of the change of color associated with the spin transition in FeII coordination compounds. The last sections encompass the study of dendrimer and lipid complexes that undergo thermally induced spin crossover properties as well as a particular case of amphiphilic Fe(III) complexes exhibiting cooperative spin transition in solution.