Researchers at the BIST Community centre ICN2 have developed novel thermochromic compounds capable of reversibly changing from colourless to coloured when heated. This functionality opens the door to promising applications in diverse areas such as product labelling and security inks, as well as in photoprotective coatings for smart windows.
In recent years, the Nanosfun (Nanostructured Functional Materials) Group at the Catalan Institute of Nanoscience and Nanotechnology (ICN2) has established itself as a leading international reference in the design of functional thermochromic materials – materials that change colour when heated or cooled.
In their latest study, led by CSIC Prof. Daniel Ruiz and Dr. Claudio Roscini, the team presents materials that are colourless at room temperature but become coloured when heated. This behaviour is difficult to achieve and opens up a wide range of industrial possibilities. Their work, which also involved researchers Noel Muñoz and Diptiman Dinda, has recently been published in the journal Small.
The new material is based on a precisely designed combination of three elements: a special dye (a leuco dye), a bioinspired catechol-based activator, which triggers a colour change on contact with the dye, and a phase-change-material (a fatty acid) which melts at a specific temperature, enabling the other two components to interact.
The principle is simple: at room temperature, the mixture is colourless. When heated, the phase-change material melts, enabling the activator and dye to interact and produce a strong, clearly visible colour. While most reported materials work in the opposite way, with the interaction between the activator and the dye taking place in the solid state of the phase-change material, this new composition allows colour to appear when heated.
This has several advantages: an invisible, colourless state at low temperatures, which is ideal for security inks, and colour development at high temperatures, which is much more visible to the naked eye than colour fading and is therefore useful for colour-based temperature sensors. By adjusting the composition of the mixture, the researchers can precisely control both the temperature at which the colour change occurs and the resulting colour, making the system highly adaptable for different applications.
This advance represents a significant milestone in the development of a new generation of smart thermochromic materials that can respond visually to temperature changes. Potential applications include temperature sensors and ‘invisible’ inks and security features for product labelling to help prevent counterfeiting – an area in which the spin-off company Distinkt has emerged as a key player in recent years. This work once again demonstrates how nanotechnology can transform everyday materials into advanced technological solutions that enhance many aspects of daily life.
Reference article:
Dinda, D; Muñoz Pérez, N; Faraudo, J; Ruiz‑Molina, D; Roscini, C. High‑Contrast Colorless‑to‑Colored Thermochromic Materials. Small. (2025). DOI: https://doi.org/10.1002/smll.202511454
