Spin crossover in metallomesogens

In this review article are illustrated the strategies developed in order to achieve interplay/synergy between spin transition and liquid crystal transition. The synthesised Fe(II) metallomesogens exhibit different types of interplay between both phase transitions. A classification according to the analysis of the magnetic and structural data has led to the separation of three types of interplay, namely: type i systems with coupled phase transitions, subdivided into three groups a, b and c (in a the structural changes associated with the Cr ↔ LC drive the spin transition while in b these structural changes influence the spin state of the metallic centers but they are not the driving force of the spin state transition; and c concerns the systems where the vitrification of the material inhibits the SCO properties); type ii: systems where both transitions coexist in the same temperature region but are not coupled due to competition with the dehydration; type iii: systems where both transitions occur in different temperature regions and therefore are uncoupled. The synthesised Fe(II) metallomesogens present thermochromism in the room temperature region. By exploiting the fluid nature of these bi-functional materials it is possible to prepare thermochromic thin films of a few μm.