Periodic Reporting for period 4 - MECHANO-FLUO (Mechanofluorochromism: from molecular engineering to the elaboration of smart materials)
Reporting period: 2021-09-01 to 2023-02-28
Fluorescent materials, designed through appropriate molecular engineering, are able to signal different stimuli with a high sensitivity, in a non-destructive manner. In particular, mechanofluorochromism relates to fluorescent compounds for which emission spectrum in the solid state changes upon application of a mechanical stimulus. The interest for this phenomenon has enormously increased for the last 10 years but many examples remain qualitative: neither the nature of the mechanical stress (pressure, shearing force…) that triggers the fluorescence changes nor its intensity are known.
The overall objective of the MECHANO-FLUO project is to prepare mechanofluorochromic
molecules and materials, understand and tune their photophysical and mechanofluorochromic
properties, and implement these new materials as quantitative mechanical force sensors. To achieve this overall objective, several work packages are defined:
- The first one comprises the synthesis of a small library of mechanofluorochromic molecules, in our group or in external collaborations. Over the course of the project, several families of compounds have been studied. We have achieved a better comprehension of the origin of their sensitivity to mechanical forces and we have obtained promising molecular materials for the others parts of the project.
- In the second work package, we have studied mechanofluorochromism at the micro- to nanoscale. We have developed a protocol allowing to follow the mechanofluorochromic response of structurally diverse materials. This is a crucial step in order to develop nanostructured materials allowing local force measurements, and to quantify their sensitivity.
- The third work package covers the quantification of the mechanofluorochromic response at the macroscopic scale. Different setups have been developed to allow this quantification on molecular materials (powder or thin films) and on polymers. Work continues to evaluate the potential applications in stress metrology: fluorescent materials with a quantitative mechanofluorochromic response could give access to the stress level in various materials and thus constitute an entirely new method for in situ control of the damaging of materials.
- In the fourth work package, we have developed biocompatible mechanofluorochromic materials, in the form thin layers covering the inside of microfluidic channels. We are studying the sensitivity of these thin layers to the friction exerted by microalgaes. In the future, we hope to extend this work in order to provide a tool for direct force measurement at the cellular scale. This would have tremendous implications for the comprehension of biological phenomena where mechanotransduction is implied, such as tumour proliferation.
While the first two work packages mainly have implications in the field of materials chemistry (beyond mechanofluorochromism, a better understanding of the sensitivity of fluorescent materials to forces is useful for different applications, such as the development of flexible organic electronics devices), the third and fourth work packages aim at providing innovative tools in other fields of science, namely solid state mechanics and mechanobiology.
The overall objective of the MECHANO-FLUO project is to prepare mechanofluorochromic
molecules and materials, understand and tune their photophysical and mechanofluorochromic
properties, and implement these new materials as quantitative mechanical force sensors. To achieve this overall objective, several work packages are defined:
- The first one comprises the synthesis of a small library of mechanofluorochromic molecules, in our group or in external collaborations. Over the course of the project, several families of compounds have been studied. We have achieved a better comprehension of the origin of their sensitivity to mechanical forces and we have obtained promising molecular materials for the others parts of the project.
- In the second work package, we have studied mechanofluorochromism at the micro- to nanoscale. We have developed a protocol allowing to follow the mechanofluorochromic response of structurally diverse materials. This is a crucial step in order to develop nanostructured materials allowing local force measurements, and to quantify their sensitivity.
- The third work package covers the quantification of the mechanofluorochromic response at the macroscopic scale. Different setups have been developed to allow this quantification on molecular materials (powder or thin films) and on polymers. Work continues to evaluate the potential applications in stress metrology: fluorescent materials with a quantitative mechanofluorochromic response could give access to the stress level in various materials and thus constitute an entirely new method for in situ control of the damaging of materials.
- In the fourth work package, we have developed biocompatible mechanofluorochromic materials, in the form thin layers covering the inside of microfluidic channels. We are studying the sensitivity of these thin layers to the friction exerted by microalgaes. In the future, we hope to extend this work in order to provide a tool for direct force measurement at the cellular scale. This would have tremendous implications for the comprehension of biological phenomena where mechanotransduction is implied, such as tumour proliferation.
While the first two work packages mainly have implications in the field of materials chemistry (beyond mechanofluorochromism, a better understanding of the sensitivity of fluorescent materials to forces is useful for different applications, such as the development of flexible organic electronics devices), the third and fourth work packages aim at providing innovative tools in other fields of science, namely solid state mechanics and mechanobiology.
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.
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.
The understanding of the molecular origins of mechanofluorochromism on boron diketonate complexes clearly represents a progress beyond the state of the art in the field, and provides us solid bases to develop performant new compounds in this family. The study of the “mechano-CPL” effect is fully unprecedented.
Concerning the study at the nanoscale, we successfully showed for the 1st time, on compounds displaying an off to on fluorescence switch, that the fluorescence intensity observed after mechanical stimulation increased with the force applied. We have also studied another family of compounds and we have shown that in this case the mechanofluorochromic responses at the macroscale and nanoscale were different.
Concerning the quantification of mechanofluorochromism at the macroscale, the setup and analysis protocol we developed allowed us to obtain the compression and shearing thresholds necessary to observe a change in fluorescence. This undoubtedly represents a progress beyond the state of the art of the field. The fact that we have been able to obtain mechanofluorochromic polymers sensitive to friction forces is also unprecedented.
A proof of principle has been obtained for the WP4 “probing forces in biological systems”: we have been able to graft mechanofluorochromic thin films into microfluidic channels and to show that these coatings were sensitive enough to detect the friction force exerted by microalgae. This is a significant progress, beyond the state of the art.
Concerning the study at the nanoscale, we successfully showed for the 1st time, on compounds displaying an off to on fluorescence switch, that the fluorescence intensity observed after mechanical stimulation increased with the force applied. We have also studied another family of compounds and we have shown that in this case the mechanofluorochromic responses at the macroscale and nanoscale were different.
Concerning the quantification of mechanofluorochromism at the macroscale, the setup and analysis protocol we developed allowed us to obtain the compression and shearing thresholds necessary to observe a change in fluorescence. This undoubtedly represents a progress beyond the state of the art of the field. The fact that we have been able to obtain mechanofluorochromic polymers sensitive to friction forces is also unprecedented.
A proof of principle has been obtained for the WP4 “probing forces in biological systems”: we have been able to graft mechanofluorochromic thin films into microfluidic channels and to show that these coatings were sensitive enough to detect the friction force exerted by microalgae. This is a significant progress, beyond the state of the art.