Fluorescence and X-ray detected reversible switching of photochromic nanostructures

Ultrathin films of organic photochromic material (fulgides) are prepared via UHV-deposition on helium-cooled substrates. Controlled annealing results in two different types of nanostructures: amorphous dots of tunable size and nanocrystals. Both forms are stable at room temperature. Interconversion between the two photochromic isomers, the colorless E- and the colored C-isomer, can be achieved by irradiation with UV or visible light, respectively. Reversible optical switching of single dots is monitored by confocal fluorescence microscopy. For nanocrystals the isomeric state is monitored by optical-absorption spectroscopy and by X-ray Bragg diffraction.