Bright Phosphorescence of All-Organic Chromophores Confined within Water-Soluble Silica Nanoparticles

Room temperature phosphorescence is usually a prerogative of metal complexes. Molecules with a hexakis(phenylthio)benzene core constitute a rare example of all-organic chromophores with phosphorescence induced by environmental rigidification. Here we report covalent encapsulation of functionalized persulfurated benzene chromophores into silica nanoparticles as a method of rigidification for induction of phosphorescence. The developed nanoparticles display bright phosphorescence at ambient temperatures and possess high colloidal stability in water. The method permits incorporation of a large number of chromophores (ca. 40) per nanoparticle while preserving their emissivity. The luminescence of the nanoparticles is sensitive to quenching by molecular oxygen in the physiological oxygen range, potentially making them suitable as probes for phosphorescence lifetime imaging of oxygen in biological systems.