Dansyl fluorescence and local structure of dansyl-labeled core-shell and core-hair type microspheres in solution

Core-shell type microspheres with fluorescent dansyl groups at random sites in crosslinked poly(N-isopropylacrylamide) (PNIPAM) shell chains and core-hair type microspheres with dansyl groups at terminals sites of PNIPAM hair chains graft-polymerized with living-radical mechanism were prepared. Fluorescent spectra indicating the microenvironments of dansyl groups attached to the microspheres and their dependences on temperature and solvent compositions were compared to those of dansyl groups in PNIPAM bulk gels and in free solutions. Fluorescence peak wavelength of dansyl groups are incorporated in the semi-interpenetrating polymer network (SIPN) region of the core-shell boundary. This is supported by a confocal laser-scanning fluorescence microscope (CLFM) image of a single particle for the core-shell type microsphere. Dansyl groups at the cain ends of PNIPAN hairs of the core-hair type microspheres in water are also located on the surface of hydrophobic cores.