Ferrocenyl dendrimers incorporated into mesoporous silica:: New hybrid redox-active materials

A novel type of redox-active materials, which to our knowledge are the first examples of mesoporous silica hosts containing dendritic guest molecules within their highly ordered channels, is presented. A simple and efficient synthetic route has been used to incorporate poly(propyleneimine) dendrimers containing 4, 8, and 64 amidoferrocenyl moieties (1-3) into MCM-41. In these new composite materials (dend-n-MCM-41, n = 1-3) the integrity of the guest after the inclusion process is maintained (as confirmed by elemental analyses, IR, and C-13 CP MAS NMR spectroscopy), resulting in stable dendrimer- matrix complexes. X-ray diffraction, nitrogen adsorption isotherms, and transmission electron microscopy are consistent with the full occupancy of the channels by the smallest dendrimer, whereas less effective inclusion is obtained with the bulkier macromolecules. One significant feature of these new composite materials is that the guest dendrimers, containing a controlled number of ferrocenyl units, are easily accessible to electrochemical oxidation. Platinum disk electrodes coated with layers of dend-n-MCM-41/graphite powder/polystyrene composites have been studied by cyclic voltammetry and differential pulse voltammetry. The electrochemical properties of these hybrid materials are related to the dendrimers different sizes and were found to differ significantly from those of the corresponding hybrid materials prepared with a nonporous silica.