Dye-labeled poly(organosiloxane) microgels with core-shell architecture

Poly(organosiloxane) microgels are highly cross-linked rather monodisperse spherical particles of radius about 10 nm. Using a functionalized silane co monomer, i.e., (chlorobenzyl)trimethoxysilane, model particles suitable for studies in colloid physics are available: photoreactive and fluorescent dy es can be covalently bound within the microgels to prepare tracers for diff usion studies using forced Rayleigh scattering (FRS) and fluorescence corre lation spectroscopy (FCS). For the application as tracer particles, it is i mportant not to influence the diffusion behavior by the coupled chromophore s. Therefore, functionalized precursors with a core-shell architecture are used to minimize labeling effects. The photochromic dye ortho-nitrostilbene (ONS) and the fluorophores rhodamine B, coumarin 343, and pyrene, respecti vely, were then coupled to the functionalized cores. The dye content of the labeled mu-gels strongly decreases with increasing thickness of the protec tive shell. A higher polarity of the used chromophores also lowers the dye content significantly, while differences in the size of the used label mole cules are less important. The fluorescence intensity of the dye-labeled sph eres is also influenced by the size of the protective shell which has been explained by differences in mobility of the labels (caging effects) and, at high dye concentration (thinner shell), by reabsorption.