One dye fits all: new materials with multiple fluorescence modes for different applications

by Virginia Greco

A team of researchers led by members of the ICN2 Nanostructured Functional Materials Group has developed a technology that allows creating photo- and thermo-responsive fluorescent materials starting from a unique dye, while adapting the matrix in which it is dispersed. This approach simplifies the applicability of fluorescence switching materials, in particular in anticounterfeiting and optical sensing technologies.

Fluorescent materials that switch on and off or change colour upon an external stimulus are attracting a lot of interest for a variety of applications, ranging from optical memories, to sensing, to anti-counterfeiting technologies. Different fluorescence switching modes can be used according to the specific needs. But, for each case, a specific dye must be designed and synthesized, which limits the general applicability of this technology. In contrast, a system in which several types of emission switching can be achieved using the same dye is highly sought after.

A team of researchers from the ICN2 Nanostructured Functional Materials Group (Nanosfun) and from the Universitat Autónoma de Barcelona (UAB) has achieved this objective by reversing the modulation approach: in their system, what changes under the effect of the external stimulus is not the dye, which is fixed, but the material (or, the matrix) where it is dissolved. As explained in a scientific paper recently published in Advanced Optical Materials –with Dr Claudio Roscini (ICN2) and Dr Jordi Hernando (UAB) as corresponding authors, and Jaume Ramón Otaegui (ICN2) as first author— the researchers adopted phase charge materials (PCMs) as matrices, since they can pass from a solid to a liquid state under photo-thermal heating. It has been recently proven that such state change produces a modulation of the fluorescence emitted by the dye immersed in them.

The authors of the study demonstrated that this approach is successful by designing and testing a system based on the phase change material called eicosane (EC), used as the matrix, and a fluorophore called (in short) PDI, as the unique fluorescent dye. The latter presents multiple emissive response that can be activated by means of different stimuli; specifically, its fluorescence can be turned from green to red and, with the inclusion of an additive, an off/on switching can be achieved. In addition, by slightly changing the matrix (in this case, EC is combined with another PCM), the thermo-responsive on/off switching can also be obtained.

As highlighted in the article, this approach can be generalized to other fluorescence emitting substances and the dye-matrix mixture can be applied on substrates, such as paper, flat glass, and polystyrene films. The scientists also used it to deposit patterns on surfaces, which they could later turn on and off, or even switch between patterns, using different stimulus conditions.

The use of a unique dye for multiple fluorescence modulation, as achieved in this study, simplifies the production of smart materials whose fluorescence response changes according to some external stimulus (generally, light or temperature) and which can provide new options for application in anti-counterfeiting and optical sensing, among others.

Reference article:

Jaume Ramon Otaegui, Aleix Carrascull-Marín, Daniel Ruiz-Molina, Jordi Hernando, Claudio Roscini, Multimodal Fluorescence Switching Materials: One Dye to Have Them All. Advanced Optical Materials, volume 10, issue 18, 2022. DOI: 10.1002/adom.202200083