These compounds change color irreversibly after surpassing a certain temperature

Scientists at CNRS have synthesized copper-based compounds whose luminescence changes color irreversibly once a critical temperature is exceeded. This color change, a unique indicator of the thermal history of their environment, is of interest for developing innovative non-destructive testing procedures.


Recent events have clearly highlighted modern societies' dependence on sources of strategic raw materials. This crucial dependence is notably evident in the domain of luminescent materials used daily in screens (mobile phones, computers) and numerous detection applications. Indeed, luminescence properties are often generated by photoactive derivatives based on heavy, precious and/or rare atoms, which sometimes present significant toxicities. This heavily limits their large-scale use.

In this context, luminescent materials based on Cu(I) ions are particularly attractive given their low cost and the natural abundance of copper. Additionally, their flexible molecular structure, which can be easily modified by applying external stimuli (temperature, pressure...), allows for modulation of their luminescence characteristics.

Chemists from the Institute of Chemical Sciences of Rennes (CNRS/University of Rennes/ENSCR/INSA Rennes) have developed a simple and rapid synthesis of a wide range of metallic complexes exhibiting remarkable photoluminescence properties at room temperature.

For this synthesis, the scientists devised a luminescent precursor made up of four Cu(I) ions linked by organic molecules, the nature of which allows for tuning the emission wavelength. They then observed an irreversible color change in the solid-state emission of the material above a specific temperature distinct to each compound. They attributed the origin of this unprecedented transition to a dissociation of the polymeric structure of these assemblies activated by crossing a temperature threshold.

Such original behaviors are a direct result of the great flexibility of the luminescent Cu(I) ion-based precursor assemblies. It is possible to dissociate these structures by increasing the temperature while maintaining the molecular structure of the precursor intact within the new material responsible for the luminescence. This new material then presents luminescence that is significantly different from that of the initial polymeric assembly.

This novel property makes these materials indicators of the thermal history of their environment. Consequently, it is possible to envision incorporating them into technological devices to ensure they have not exceeded certain temperatures for proper functionality. These findings are published in the journal Adv. Opt. Mater.

Writer: CCdM

Reference:
A. Schlachter, F. Moutier, R. Utrera-Melero, J. Schiller, A. Moustafa Khalil, G. Calvez, M. Scheer, K. Costuas & C. Lescop.
Photoluminescent Cu(I) Assemblies With High Temperature Solid-State Transitions as a New Class of Thermic History Tracers
Adv. Opt. Mater, 2024
https://onlinelibrary.wiley.com/doi/full/10.1002/adom.202400347