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Reversible switching of physical and chemical properties can be achieved by light, by means of photochromic substances. A large number of applications are sought for: protection against light, hyper-resolution microscopy, memories, etc. Moreover, photochromic molecules or moieties can be associated to other molecules or moieties with high performance in a given property for the purpose of switching. For example, materials containing photochromic and fluorescent molecules or moieties, interacting at a nanometric scale, are being investigated, for fluorescence photoswitching between OFF (no emission of light) and ON (with emission of light) states.
A general concern is to obtain big effects with small inputs. In this regard, our strategy is based on the exploitation of nanoscale interactions, such as energy transfer or plasmonic effect, in order to amplify photoswitching. In our presentation, we will focus on two aspects:
1. Accelerated photoswitching, in hybrid systems, containing gold nanoparticles and photochromic molecules. Due to plasmonic effect taking place in the gold nanoparticles, an increase of the photoswitching rate of the photochromic molecules is observed.
2. Enhanced photoswitching of fluorescence in nanoparticles containing photochromic and fluorescent moieties. The fluorescence of a large number (up to 400 moieties) can be turned ON or OFF by only one photon. This unconventional phenomenon was obserd in various systems: multichromophoric molecules, nanoparticles containing photochrome-fluorophore dyads, and silica nanoparticles grafted with photochromic and fluorescent moieties. This effect stems from the multiple energy transfer occurring at molecular and nanometric scale.
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