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Ce projet de thèse consiste dans un premier temps à synthétiser des systèmes moléculaires multifonctionnels possédants un grand nombre d’entités fluorescentes et photochromes. De telles architectures nécessitent ensuite une étude photophysique poussée pour caractériser leurs propriétés d’émission photo-activée pour jouer le rôle de sondes moléculaires fluorescentes super-résolutives en imagerie de fluorescence. En effet, l’accès aux observations nanométriques par microscopie optique est actuellement un domaine de recherche extrêmement actif et prometteur. Ici, la combinaison astucieuse de molécules photochromes (de type diaryléthène) et fluorescentes (de type dicyanométhylène pyranes ou benzophénoxazines) à l’échelle nanométrique, grâce à des plateformes moléculaires telles que des oligosaccharides et des peptides fonctionnalisés par “chimie click”, doit permettre d’obtenir des structures aux géométries variées avec des distances et orientations inter-chromophores diverses, dont l’optimisation doit conduire à des interactions efficaces menant à l’émergence d’effets collectifs coopératifs. Pour ces assemblages moléculaires mixtes, il est attendu que la présence d’une unité photochrome puisse engendrer l’extinction de fluorescence de plusieurs fluorophores lorsque ces entités sont situées à une distance appropriée pour que le transfert d’énergie ait lieu de manière amplifiée. Par ailleurs, même une faible conversion des photochromes doit permettre d’atteindre un contraste de fluorescence extrêmement efficace avoisinant 100% et ainsi obtenir des super-molécules dont la photo-commutation serait rapide et économe en photons. Il s’agira enfin de démontrer que les systèmes moléculaires multichromophoriques ainsi optimisés présentent le comportement souhaité à l’échelle de la molécule unique pour l’imagerie de fluorescence super-résolution. / The synthesis of photoswitchable emissive molecular system still represents a challenge, in order to develop fluorescence-based devices for nanotechnologies. In the last decade, excitation energy transfer processes (EET) have been advantageously employed to design photoswitchable fluorescent molecular systems between a photochromic dye and an appropriate fluorescent molecule. More recently, photochromic dyes of particular interest, showing no emission in the open-form (P-OF) but a strong emission signal in the closed-form (P-CF), have been developed. Such molecules allow a multi-emission switch when combined with a fluorescent moiety. In this project, we will design and synthesize fluorescent photochromic diarylethene covalently linked to different fluorophores, such as benzothiadiazole (BTD) and BODIPY derivatives. By choosing a fluorophore moiety with blue/green emission (F) and a photochromic moiety with orange/red emission in closed-form (P-CF), EET can occur between F and P-CF leading to photoswitchable multi-emission properties. Photophysical characteristics of dyads will be studied by spectroscopy with the aim of presenting their light-controllable optical properties and the intramolecular EET processes between fluorescent and photochromic moieties.

Light stabilisation of photochromic dyes is seen as the most challenging part in the development of photochromic dyes. The aim of this research is to compare stabilisation methods and their effect on the lifetime of a photochromic print on textile. The vision is to create a textile UV-sensor that detects current UV light exposure in the surroundings and alarms the wearer by showing colour. The developed inks have been formulated for ink-jet printing as a novel production method with resource saving properties. UV-LED light curable ink formulations were prepared for two dye classes; a non-commercial spirooxazine, a commercial spirooxazine (Oxford Blue) and a commercial naphthopyran (Ruby Red). Two different stabilisation methods were applied; chemically by incorporation of hindered amine light stabilisers and physically by polyurethane coating. Fatigue tests were performed to evaluate and compare the stabilisation methods. The tests included were household washing, multiple activations and intensive sun-lamp exposure. As a result it was found that Oxford Blue and spirooxazine had an initial better resistance to photodegradation than Ruby Red. The coating reduced the ability of colour development in higher extend for Oxford Blue and spirooxazine compared to Ruby Red. Moreover, the photocolouration increased with the number of activations for Oxford Blue and spirooxazine in particular. In general, the physically stabilised samples showed a better or similar fatigue resistance compared to chemically stabilised samples. On the other hand the results are weak in significance. It is concluded that the developed coating method in combination with further optimising has potential.