No abstract

Core/shell‐structured viologen‐modified Stöber silica particles with diameters of approximately 235 nm are prepared in a stepwise, solid‐phase synthesis. The nonporous and spherical silica base particles are obtained through a sol–gel process from tetraethoxysilane followed by a post‐synthetic calcination step and characterized by means of scanning electron microscopy, nitrogen adsorption/desorption experiments, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, Gay‐Lussac pycnometry in water, and dynamic light scattering. Coating with triethoxysilane yields SiH‐terminated particles, which are further reacted with the linker, 11‐bromo‐1‐undecene, in a thermally induced hydrosilylation. The resulting kinetically inert and thermodynamically stable SiC bond ensures strong attachment to the silica surface. The viologen units are generated by alkylation with 1‐methyl[4,4′]bipyridinium iodide directly on the particle surface. The successful attachment is confirmed by diffuse reflectance UV/Vis, DRIFT, and 13C cross‐polarization/magic‐angle spinning nuclear magnetic resonance spectroscopy. The viologen shell of the particles is electrochemically addressable. In cyclic voltammetry experiments, under three‐phase junction conditions with modified gold and paraffin‐impregnated graphite electrodes, the immobilized viologen units are reduced to the neutral state in two consecutive electron‐transfer reactions via a mono radical cation species. The in situ electrolysis of suspended particles leads to a material with a diamagnetic core (silica) and a paramagnetic shell (viologen mono radical cations). Electron paramagnetic resonance experiments demonstrate that the radical cations are strongly attached to the particle surface. The material and electrochemical properties of the particles are compared to amorphous silica and to a viologen‐modified Stöber material based on a well‐established immobilization strategy (condensation of alkoxysilane to surface silanol groups).