• Universitat de València

Spin transition compounds (SCO spin crossover) are coordination complexes that have the ability to switch between two states of different electronic configuration. The most exploited stimulus when inducing the SCO phenomenon is temperature. Generally, these compounds present durability and stability problems since together with the spin transition there is an important 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 devices to a single use (or a few). 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 compounds, two requirements must be met: they must be processable and have a robust and reproducible spin transition reversibility. These factors greatly limit the materials available.

Research staff from the UV 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 compound because we have detected that this material has a linear dependence of its transparency on temperature long before the transition temperature (-160ºC), in this way we can know the temperature of the film through its absorption spectrum. On the other hand, a good contrast in transparency has been demonstrated in the range of interest for both industrial and domestic applications.

In summary, it is possible to solve the problems that most of these materials present in devices, such as their number of uses and the robustness of the resulting devices. Furthermore, the complexity of the manufacturing device is relatively low, since for the present invention it only requires the material itself deposited on a substrate such as a film, using a tiny amount of it, and a simple camera that captures light through this film or the light reflected by it.

Nanometric temperature sensor for:

• Aeronautics
• Automotive
• Home automation
• Scientific instruments

Thermo-optical switch for applications close to room temperature.

Some of the advantages it presents are:

• Miniaturization of optical devices and sensors by being able to use films around 10 nm thick.
• Minimum thermal inertia.
• Simple and compact device design.
• Possibility of carrying out measurements remotely, in closed environments and without cables.
• Longer lifespan than most similar devices
• Reduction in response times compared to proposals with similar materials.

• Patent granted