In WP1 several new molecules have been prepared and studied, in our group and through national or international collaborations. In particular, we have developed a series of boron diketonate complexes for we which we have been able to identify the emissive species before and after mechanical stimulation, in collaboration with computational chemists (Dr. I. Ciofini, Paris – Adv. Mater., 2018). In collaboration with Prof T. Kawai (NAIST, Japan), we have developed the first compounds that are mechanofluorochromic and at the same time CPL (Circularly Polarized Luminescence) emitters, and display a change in CPL emission upon mechanical stimulation (Chem. Sci., 2019). Overall, the results obtained in this work package have led to 10 publications.
In WP2, a method to study mechanofluorochromism at the nanoscale has been developed. Three families of compounds have been studied. The first study has been published in J. Phys. Chem. Letters (2019). The second family of compounds studied display an off to on fluorescence emission switch upon shearing. We have shown that the fluorescence intensity observed after mechanical stimulation increases with the force applied, in the 20-200 nN range (Chem. Commun.(2019), PCCP (2021)). In a third family of compounds we have evidenced the reversibility of the mechanofluorochromic shift at the submicroscale (Adv. Mater. Interfaces, 2022).
For the quantification of mechanofluorochromism at the macroscale (WP3), a device has been built in collaboration with Dr. L. Bodelot (Laboratoire de Mécanique des Solides, Ecole Polytechnique, France) to quantify the forces that can trigger the fluorescence changes on a molecular solid. Several compounds have been studied and revealed a much higher sensitivity to shearing stress than to compression (J. Mater. Chem. C, 2021). Mechanofluorochromic polymers have been prepared and they revealed sensitive to traction and friction forces, with different emission colour changes (Macromolecular Rapid Communications, 2022).
Concerning the application of mechanofluorochromic compounds to measure forces in biology at the cellular scale, we have established a collaboration with B. Le Pioufle and S. Bensalem (Lumin, ENS Paris-Saclay, France). They evidenced earlier that flowing microalgae through microfluidic channels with size restriction enabled to exert mechanical stress on their cell wall. We have been able to graft a mechanofluorochromic thin layer inside these microfluidic channels and to show that the flow of microalgae triggered the mechanofluorochromic response. A first publication on this topic has been submitted, work will continue towards the quantification of the force exerted by the microalgae.
