Modified electrodes from organic-inorganic hybrid gels formed by hydrolysis-polycondensation of some trimethoxysilylferrocenes

Gels formed from trimethoxysilylferrocene 1 and 1,1'-bis(trimethoxysilyl)ferrocene 2 copolymerized with tetramethoxysilane have been deposited onto platinum, and allow the building of modified electrodes with interesting electrochemical properties. The electrochemical response of the gels has been found to be strongly dependent on the starting molecule and its concentration, but only weakly on the electrolyte nature. Special attention has been paid to the dynamics of the electron transfer through the gels, and a quantitative analysis has been performed in various cases. While the gels prepared from the disilylated ferrocene 2 display, like several different functionalized polymers, a Cottrellian diffusion of the charge transfer (in accordance with the classical theoretical treatment of Andrieux and Saveant), in the gels formed from the monosilylated ferrocene 1, the charge transfer follows a power law with a fractional exponent. This unique behaviour is indicative of a particular substructure in the gels, with the ferrocene moieties probably positioned at the surface of accessible silica particles.