Description of the thesis topic

Soft materials displaying switchable luminescence properties in response to external stimuli are of great interest for applications in strain detection, sensor, optical recording, storage and anti-counterfeiting... Liquid crystal elastomers (LCEs), made of polymerisable liquid crystalline molecules able to self-organized in the liquid state, linked together by a cross-linkers, are an interesting class of polymers capable of undergoing large deformation with increase up to 400% of their initial size under mechanical stress or temperature change. Luminescent mechanochromic compounds are characterized by a change of their luminescence properties in response to mechanical constrains. Thus, the chemical integration of luminescent mechanochromic compounds within LCEs is expected to enable the development of highly responsive and original luminescent mechanochromic soft materials.
The aim of the present project is thus to use mechanochromic cross-linkers to develop stimuli-responsive polymer materials whose luminescence properties will be sensitive to mechanical constraints and temperature changes. For this purpose, polymerisable copper iodide cubane complexes [Cu4I4L4], known for their good mechanochromic properties, will be developed and used as cross-linkers for the preparation of elastomers (Scheme 1). The contraction and the elongation of the elastomers at the liquid crystal to isotropic phase transitions will directly apply mechanical constraints onto the complex core inducing modification of their luminescence properties. Molecular organization and luminescence switching as a function of temperature changes and/or mechanical stress will be characterized by state-of-the-art techniques such as small-angle X-ray diffraction, dynamic mechanical analysis and temperature epifluorescence. In a second step, photoresponsive mechanochromic luminescent materials will be developed by introducing a photothermal cross-linker in addition to the mechanochromic cross-linker. Such light responsive materials present wide application perspectives in control devices, soft-robotic and biomimetic devices.

Work Context

This thesis will be carried out at the Institut des Sciences Chimiques de Rennes (ISCR) as part of an ANR project in collaboration with the Institut des Matériaux de Nantes (IMN) and the Laboratoire Sciences et Ingénierie de la Matière Molle de Sorbonne Université (SIMM). This thesis will be supervised by Franck Camerel (DR, CNRS) at ISCR, who is an expert in soft materials. The PhD student will be responsible for synthesizing and characterizing mechanochromic crosslinkers, incorporating them into polymers, and assessing their processability and reactivity under various external stimuli, including laser irradiation. Working in a multi-disciplinary consortium will enable the PhD student to acquire additional and complementary skills in a variety of cutting-edge techniques, and to discover different working environments and practices.

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.

Constraints and risks

The Ph.D candidate will have to master synthesis techniques (organic chemistry, purification and characterization techniques). This project needs a motivated student willing to develop their skills and knowledge in synthesis, characterization of polymers (DSC, POM, SAXS, DMA), spectroscopic characterization and coordination chemistry. A good English level and knowledge on polymer chemistry would be a plus.