Photoswitchable and/or multicolor fluorescent nanoparticles can be prepared by incorporation of photochromic dithienylethene or spiropyran derivatives in silica.
When these compounds are converted into their coloured form, they are able to quench the fluorescence of selected dyes via an energy transfer mechanism.
We synthesized new photoswitchable silica nanoparticles by different approaches:
(1) Dithienylethenes were incorporated in the outer shell of dye-doped core-shell nanoparticles, close enough to the dyes entrapped in the core to efficiently quench their fluorescent states by energy transfer when photoconverted with UV light. The emission can be switched on again by irradiation with visible light.
(2) A second type of switchable fluorescent silica nanoparticle was prepared by covalently incorporating both a rhodamine B (fluorophore) and a spiropyran (photochromic compound) inside the particle core. Again the fluorescence can be switched reversibly between an on- and off-state (see animation). The particles were characterized in terms of size, switching properties, and fluorescence efficiency by TEM, UV-Vis and fluorescence spectroscopy.
These NPs with photoswitchable fluorescence have commercial relevance in the market of labelling agents for high resolution optical imaging in relation with Super-Resolution fluorescence microscope systems recently developed and made commercially available by few microscopy companies. Super-Resolution (SR) microscopy includes various recently developed methods in fluorescence-based light microscopy that have by-passed the resolution limit imposed by diffraction on lens based optical systems. These SR imaging methods show great promise as a research tool for basic biological research as they have the theoretical potential to achieve resolutions equaling those of electron microscopy, while also being far less expensive and less invasive.
 D. Genovese, M. Montalti, L. Prodi, E. Rampazzo, N. Zaccheroni, O. Tosic, K. Altenhöner, F. May, J. Mattay, Chem. Commun.2011, 47, 10975–10977. [10.1039/c1cc14800a]
 F. May, M. Peter, A. Hütten, L. Prodi, J. Mattay, Chem. Eur. J.2012, 18, 814–821. [10.1002/chem.201102961]
 B. Seefeldt, K. Altenhöner, O. Tosic, T. Geisler, M. Sauer, J. Mattay, Photochem. Photobiol. Sci.2011, 10, 1488–1495. [10.1039/c1pp05051f]