Research axis 1

New photoswitchable organic fluorescent nanoparticles: Dr. M. Sliwa, Pr. J. Abe

a) Photo-switchable NP with fast thermal back reaction.

Fast switchable fluorescent probes and fast & accurate data analyses require the consideration of multifold parameters: different labeling densities, the inter-dependence of blinking parameters for neighbored emitters, and finally the presence of inhomogeneous complex backgrounds, which are still key issues in super-resolution far field fluorescence microscopy. The target of this task is to understand the emission dynamics of organic fluorescent nanoparticles at the nanometer scale, especially the underlying cooperative processes arising in nanoparticles. The Lille Univ. group will use a whole range of ultrafast microscopy systems to characterize the energy & electron transfer involved in nanoparticles fabricated at ENS Paris-Saclay out of new molecules (rylene, fluorescent Fast-HABI) synthesized in Japan. Cooperative effects and multiphoton processes are foreseen and will be studied by Pr. H. Miyasaka group (Osaka Univ.) while the group of Pr. J. Abe (Aoyama Gakuin Univ.) will be in charge of the synthesis of the novel molecules. Within this task, Japanese students & researchers are planned to stay to study the system using ultrafast IR spectroscopy, RESOLFT & femtosecond microscopy, EPR imaging spectroscopy, and learn to use new data analysis methods for time-resolved spectroscopy & high resolution localization microscopy.


b) Development of ultra-high sensitivity photoresponsive organic NPs by giant amplification effects based on cooperativity of the molecular assemblies.

ENS Paris-Saclay demonstrated unique photochromic properties of nanoparticles or crystals, which differ from those observed in solution or bulk solid. These findings open the way to the development of highly efficient fluorescent and photo-switchable molecular nanoparticles. The switching properties of nanoparticles are expected to be improved compared to individual molecules, since intramolecular energy transfer but also long distance intermolecular energy transfer may occur. Indeed, the photochemical reaction of a small amount of molecules in nanoparticles results in energy trap sites, and consequently, amplified quenching phenomena are expected to occur with non-linear fluorescence changes. To achieve this concept, high photo-reactivity and excellent emissive properties of the nanoparticles are required. Therefore, within this task we plan to i) design and synthesize photoswitchable fluorescent molecules and NPs (ENS Paris-Saclay –); (ii) measure their properties by using imaging fluorescence microscopy and perform femtosecond-picosecond time-resolved spectroscopy of the photoresponsive molecular systems in solution and in the nanoparticles state (Lille Univ.). Optical control and mechanism elucidation of molecular assemblies with nonlinear formation behavior through cooperative association will be studied. Finally, we will also consider the application of the ultra-high sensitivity and giant amplification effects generated in the photoactive nanoparticles to the field of super-resolution fluorescence imaging or bio-imaging.

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