Förster Resonance Energy Transfer (FRET) enables the exciton diffusion between molecules through a characteristic distance of 1 to 10 nm. The association of multiple fluorophores represents a solution to facilitate exciton diffusion over a longer range, taking profit of homo-FRET and hetero-FRET phenomena. FRET is a fundamental aspect in the development of photo-switchable luminescent devices. At the molecular level, the design of photo-switchable systems relies on the association of two components: a luminescent material and a photochromic compound. The formation of nano-objects with similar molecules leads to intriguing responses in fluorescence and photochromic behavior due to multiple energy transfers. However, these systems are poorly used in molecular logic, and they switch between bright and dark states. Considering an emissive acceptor (a second bright state) would allow exciton diffusion over longer distances and enable its detection.

The FLUOGATE project objective is the preparation and characterization of photoswitchable luminescent molecular nanostructures that behaves as an excitonic gate. The initial step is the preparation and study of 2D photoswitchable monolayers with controlled organization. The combination of optical and local probe measurements will permit the characterization of fluorescence photoswitching following the structural change at the single molecule scale and determination of the quenching radius. Then, the preparation and study of 3D architectures will be undertaken. The strategy entails the successive deposition of various dyes. Layers of the donor fluorophore will be deposited just above the substrate, followed by layers of the photochromic compound and finally layers of the acceptor fluorophore. The ultimate goal will consist in exploring the replacement of the photochromic layer by a photochromic nanoparticle in a polymer matrix.