USE OF TRANSITION SPIN FILM COMPOSITE AS A TEMPERATURE SENSOR

Spin crossover (SCO) compounds are coordination complexes that have the ability to switch between two states of different electronic configuration. The most exploited stimulus to induce the SCO phenomenon is temperature. Generally, such compounds present durability and stability problems because together with the spin transition there is a significant change in the volume of the material. As a consequence, the films lose their initial structure after a few temperature cycles, limiting their applicability in single (or few) use devices. In fact, most patents in thermo-optical switching use other types of materials. In order to make real use of the properties of spin transition composites, two requirements must be met: they must be processable and have robust and reproducible spin transition reversibility. These factors greatly limit the available materials. UV research personnel have developed the present invention in relation to the use of the spin transition molecular compound [iron(ii)(hydrotris(3,5-dimethyl-1-pyrazolyl)borate)2] in thin film format for applications in devices such as thermo-optical switch and optical temperature sensor in the range between -70 and 50 °C. Unlike other proposals, the patented method consists of working at temperatures far from the transition. In this way, we avoid the volume change in the material and thus solve the problem of structural stability of SCO composites in film form. This is possible in our composite because we have detected that this material presents a linear dependence of its transparency with temperature long before the transition temperature (-160ºC), so we can know the temperature of the film through its absorption spectrum. On the other hand, it has been demonstrated a good contrast in transparency in the range of interest for both industrial and domestic applications. In summary, it is possible to solve the problems presented by most of these materials in devices, such as their number of uses and the robustness of the resulting devices. In addition, the complexity of the manufacturable device is relatively low, since the present invention only requires the material itself deposited on a substrate as a film, using a very small amount of the same, and a simple camera that captures the light through this film or the light reflected by the same.