LAUSR

The spectroscopic properties of silica nanoparticles decorated with fluorescent photochromic molecules at their surface were studied by combining UV–visible spectroscopy with fluorescence correlation spectroscopy on diluted samples of particles dispersed in dimethyl sulfoxide (DMSO). We have first studied the properties of the fluorescent photochromic diarylethene molecules in DMSO using two-photon excitation at 720 nm so as to induce the cyclization reaction of the photochromic molecules from the open to the closed form. This diarylethene compound is fluorescent in its open form and nonfluorescent in its closed form, so the photochromic reaction offers the opportunity of modulating the fluorescence intensity between a bright ON state and a dark OFF state. The analysis of the lifetime measurements indicates that at least three conformers contribute to the emission of fluorescence. These results are in good agreement with our density functional theory calculations, which help us to assign the conformers to...